A recent cluster of equine infectious anemia (EIA) cases has once again highlighted the importance of proper training of the individuals that work in equine veterinary clinics to help prevent the spread of disease via iatrogenic (relating to illness caused by medical examination or treatment) transmission.

A cluster of EIA-positives that were infected throughout May 2024 and another cluster from mid-June through the end of August 2024 were found to have originated at a Texas equine clinic. All the EIA-infected horses had been hospitalized in the intensive care unit (ICU) at the clinic and had an intravenous (IV) catheter placed and flushed.

As of May 30, 2025, the USDA Animal and Plant Health Inspection Service (USDA-APHIS) has identified 21 horses confirmed positive for EIA in four states—California, Colorado, Oklahoma, and Texas. The affected horses are of varying ages, breeds, and disciplines.

“I don’t believe we have found all of the exposed horses for testing just yet,” said Angela Pelzel-McCluskey, DVM, USDA-APHIS equine epidemiologist. “I think there are more that need to be added to the list.” She added that anyone who is concerned  their horse might have been exposed should contact their veterinarian and have their horse(s) tested.

The incubation period of horses infected with EIA is usually 15 to 45 days, and horses that have been infected with the virus are lifelong carriers. Horses showing clinical signs of the disease are more of a threat to healthy populations because of higher levels of the virus circulating in the blood.

Horses that survive the initial clinical phase of the disease usually become outwardly inapparent carriers and remain a lifelong reservoir for the disease. There is no treatment for the disease and no vaccine to prevent an EIA virus infection. If confirmed positive, horses are usually euthanized to prevent ongoing transmission to other horses. If not euthanized, horses must be permanently quarantined with separation from noninfected horses by at least 200 yards to prevent spread of the disease by biting flies. Infected horses cannot be moved from quarantined premises except by approval of state and federal animal health officials. Clinical signs of EIA might include fever, depression, low platelet count, anemia, red or purple spots on the mucous membranes, edema, muscle weakness, and atrophy, although chronically infected horses often show no obvious clinical signs of the disease.

Veterinarians diagnose EIA by testing antibody levels in the blood. They most commonly use the Coggins test, which is an agar gel immunodiffusion (AGID) test. An ELISA (enzyme-linked immunosorbent assay) test is also available to detect EIA antibodies. Practitioners must collect blood and submit it to certified laboratories for testing.

The USDA-APHIS has reviewed the complete medical history of the 21 horses confirmed EIA positive that were treated at the Texas clinic.

The current investigation indicated at least one or more employees of the clinic were reusing needles or syringes to draw up and flush IV catheters with heparinized saline in the ICU as a routine procedure, which caused repeated instances of blood contamination into the bottles. “The original sources of the EIA virus were likely bush-track or other high-risk horses that were admitted to the clinic ICU just prior to each cluster of cases in May and August,” said Pelzel-McCluskey.

The USDA-APHIS began investigating the cases in September 2024, when a 3-year-old Quarter Horse mare in Wise County, Texas, was confirmed EIA-positive. The horse was used for barrel racing and had no flat-track racing history, and her cohorts were EIA negative. Another Wise County case, an 8-year-old Andalusian mare with no racing or import history and with all negative cohorts, was found EIA-positive the following month. The next two months brought three more cases from the same county. The horses showed no common EIA risk factors and had no contact with each other.

“The only thing we could come up with is that all of the horses were seen by the same veterinary clinic,” Pelzel-McCluskey said. “That for a small county area is not strange, so it was a head scratcher.” She noted the horses home premises were not located adjacent to each other, so it was not a local geographic focus of natural fly-bite transmission.

Through investigation, officials determined the only common factor was that the horses had been hospitalized in either two clusters May 2024 and August 2024; three horses in May and two in August for other reasons and EIA was not diagnosed.

At the request of the USDA-APHIS, the horse owners began sharing medical records of the five infected horses. At the same time, four more cases with connections to the same veterinary clinic were discovered in January, February, and March of this year—two more horses from Wise County, one from Denton County, and one located in Oklahoma.

Pelzel-McCluskey said the next step in the investigation is to compile a more complete list of exposed horses from the clinic’s appointment book to identify horses that had an IV catheter placed at the clinic during the affected time range, while completing regulatory EIA testing of all horses that were potentially exposed. Testing will also be completed on cohorts of any new EIA-positive cases.

About 1.3 million horses per year are tested for EIA. So far in 2025 there have been 44 EIA positives. In 2024 there were 147 positive cases, and 120 of those were in the primary high-risk category of Quarter Horse racehorses that contracted the disease via iatrogenic transmission by unhygienic injection practices of owners and trainers, not veterinarians.

The rate of EIA positives has been on the rise since 2016 when there were only 44 cases recorded, with the majority being natural transmission via fly bites. The iatrogenic-transmission EIA cases now being found in Quarter Horse racehorses frequently have ties to unsanctioned or bush track racing.

“I believe that veterinary clinic owners and employees have become complacent, and people don’t believe that something like this could happen, but it does happen, and it is happening at a very large scale with a lot of negative outcomes,” Pelzel-McCluskey said. “I would like state animal health officials to reach out to remind people that we do have iatrogenic transmission of EIA, and this can occur in clinics if the expected procedures for sterile technique are not being followed by all employees at the clinic.”

By Leslie Barlow and Dr. Angela Pelzel-McCluskey for the Equine Disease Communication Center (EDCC)

Lyme isn’t the only tick-borne illness horse owners need to consider

Lyme is the tick-borne disease most people think of first, but it isn’t the only one. Anaplasmosis is another disease of clinical significance in horses, and other diseases might be on the rise (Have you heard of ehrlichiosis in horses?). In this story we’ll look at what ticks are troublesome to horses, when and where they can be found, then discuss the clinical signs, diagnosis, and treatment of anaplasmosis, the “other” tick-borne disease that always seems to take a back seat to Lyme.

Which Ticks are Found on Horses?

In the U.S., many hard ticks infest horses, including the American dog tick (Dermacentor variabilis), the winter tick (Dermacentor albipictus), the lone star tick (Amblyomma Americanum), the Gulf Coast tick (A. maculatum), and the black-legged tick (Ixodes scapularis).

“Of particular interest to horse owners and veterinarians is the ability of these ticks to transmit disease agents,” says Kathryn Duncan, DVM, PhD, Dipl. ACVM, adjunct assistant professor at Oklahoma State University, in Stillwater, who has studied the subject with colleague Kellee Sundstrom, MS, senior research specialist. “Occasionally, a foreign animal disease, such as equine piroplasmosis, is diagnosed in the U.S. Ticks can be implicated as the cause of transmission, but the tick-borne disease agents most often transmitted to horses are through a bite from Ixodes species.” 

Where Ticks are Found

Geographically Traditionally, I. scapularis are found in the eastern parts of the United States, whereas I. pacificus are found along the West Coast, including California, Washington, and Oregon, with a few reports coming from Nevada and Utah. With continued biogeographical changes, however, the “natural” ranges of ticks are evolving, experts say, and many ticks are found well outside what has been considered their traditional geographical areas.

Sonenshine et al. (2018) reported that the main reason for expansion of ticks is climate change, notably the rapidly rising global temperatures. That said, host availability and specificity, habitat suitability, relative humidity tolerance, the extent and duration of freezing temperatures, and human impact (habitat modification) all contribute. As an example of expanding tick ranges, Sonenshine et al. noted that I. scapularis densities have also intensified in many areas, and they appear to be advancing into parts of southern Canada at a rate of about 46 km (28.5 miles)/year.

Anatomically (on the Horse) In a study on horses in northeastern Oklahoma, Sundstrom et al. (2021) looked at the types of ticks infesting horses and the preferred site of attachment. Client-owned horses residing on eight farms were examined twice monthly for one year. Researchers collected ticks from those horses and recorded the anatomic location of attachment. They included 88 horses in the study, and 84.1% of horses were infested with ticks at least once during the study period.

The median number of ticks per horse was three. Researchers identified five different tick species, the most common being A. Americanum—the lone star tick (78.2%)—followed by I. scapularis, which was much less prevalent (18.2%). They found the lone star tick most often attached in the inguinal region (groin), and they found I. scapularis primarily on the chest and armpits (axilla) of the horses.

What Times of Year In that same study Sundstrom et al. also noted ticks were discovered on horses year-round in northeastern Oklahoma with the largest number seen in May. I. scapularis predominated October through February and was still common in March.

“The belief that ticks are only out in the summer is a myth that many tick researchers and veterinarians have been trying to bust for a while now,” explains Duncan. “Tick numbers may decline in the winter, but the extent to which this happens is dependent on the geographic region.”

In fact, she says that Ixodes spp and D. albipictus prefer cooler months.

“Ticks will ‘overwinter’ in leaf litter, under snow cover, and in reservoir host habitats but reemerge when there are ample hosts available and slightly warmer days,” Duncan explains. “In order to reemerge in the spring, some stages are required to survive the winters. With milder winters and premature emergence of warm weather, we can expect ticks to be noted earlier than we’ve seen in the past. This is likely a trend that will remain based on continued tick habitat changes.”

A Look at Anaplasmosis (and Some Comparisons to Lyme)

This disease is caused by an infection with Anaplasma phagocytophilum, which is a type of bacterium in the rickettsial group. These bacteria must live inside the cells of the infected animal. With anaplasmosis, the bacteria live inside white blood cells, which are also called granulocytes. This is why veterinarians also refer to anaplasmosis as equine granulocytic anaplasmosis (EGA). In contrast, the bacterial spirochete Borrelia burgdorferi causes Lyme disease.

Similar to Lyme disease, A. phagocytophilum is transmitted to horses via the bite of an infected black-legged tick—I. scapularis, I. pacificus, and other Ixodes spp. After the bite, the tick injects the bacterium into the horse’s skin. Migrating granulocytes respond to the local inflammation and engulf the bacteria, attempting to kill them.

“But A. phagocytophilum is now exactly where it wants to be, inside the cell, where it is able to avoid natural immune defenses,” says Duncan. “Disease symptoms are caused by natural immune chemicals like interferon trying to fight off the infected cells. It takes about one week before the horse begins showing signs of disease.”

Clinical Signs of Anaplasmosis

Classic clinical signs of anaplasmosis can be as mild as the horse having a fever, depression, subtle limb edema (fluid swelling), and ataxia (incoordination).

“Many horses with anaplasmosis probably don’t show any clinical signs at all,” says Janet Foley, DVM, PhD, professor in the Department of Medicine and Epidemiology at the University of California, Davis (UC Davis), School of Veterinary Medicine.

More severe signs, which typically develop in older, geriatric horses, include loss of appetite, reluctance to move, icterus (jaundice), and petechiae, which are small pinpoint bruises on the skin.

When present, the fever is quite high, usually 103-104 F, but can reach 107-108 F and lasts for about five days.

That said, tick-borne diseases are true masters of disguise, and researchers have described various other clinical presentations. John Madigan, DVM, MS, Dipl. ACVIM, a professor in the Department of Medicine and Epidemiology at the UC Davis School of Veterinary Medicine, recently published an article describing one horse with dysphagia (difficulty swallowing) and another with respiratory distress attributable to anaplasmosis (2021).

Veterinary Diagnosis

Horses with potential exposure to ticks—essentially, those in every state in the U.S.—presenting with the above-described clinical signs, particularly a high fever, should be tested for anaplasmosis.

“A horse presenting with a high-ish fever that resides in a place that overlaps
geographically with I. pacificus would definitely make you want to test for anaplasmosis,” says Foley.

Testing includes the following steps:

• A complete blood cell count. Typical findings include either a decrease in white blood cell counts or a decrease in all three cell lines: white blood cells, red blood cells, and platelets. This latter presentation is called pancytopenia.
• Microscopic analysis of the blood cells. The white blood cells might show “cytoplasmic inclusion bodies,” which are the rickettsial organisms living inside the granulocytes.
• A polymerase chain reaction (PCR) test, a molecular method for detecting DNA of the bacterium in a horse’s blood sample.
• The IDEXX SNAP 4Dx that detects antibodies to anaplasmosis. It provides a “positive” or “negative” indication for antibodies, but it does not confirm an active infection.
• An immunofluorescence antibody test (IFAT) that identifies antibodies against A. phagocytophilum. Veterinarians must interpret this result with caution, however, because many horses living in areas where hard ticks are endemic might have those antibodies.
• Acute and convalescent titers. This is an IFAT performed when the horse is first sick to measure the antibody levels, then again two to four weeks later. The antibody levels increase about fourfold in horses that have been actively infected.

Anaplasmosis must be differentiated from other diseases. Because horses can exhibit ataxia, the top differentials include viral encephalitides such as equine herpesvirus myeloencephalopathy (EHM), West Nile virus, and the Eastern and Western encephalitis viruses. Other conditions to consider are liver disease (because of the jaundice); purpura hemorrhagica, which is a secondary complication to strangles (Streptococcus equi bacterial) infection; viral arteritis; and even the reportable and highly fatal disease equine infectious anemia (EIA). 

Treating Anaplasmosis

Like Lyme disease, anaplasmosis is easily treatable. Veterinarians’ antibiotic of choice is oxytetracycline.

“There are different treatment protocols out there, but a standard full course of antibiotics is appropriate, 10 days,” says Foley.

For more severely affected horses, practitioners can administer corticosteroids in addition to intravenous fluids and nonsteroidal anti-inflammatories.

Unlike many other diseases that fail to spare the feet, few horses with anaplasmosis ever develop laminitis.

How Commonly Does Anaplasmosis Strike?

“In Northern California, anaplasmosis is actually pretty common,” says Foley.

Duncan agrees, adding, “These infections are probably more common than we realize. But considering most horses are never tested for tick-borne diseases, we can’t know for sure.”

Nonetheless, tick-borne diseases are frequently considered as causes for disease (i.e., fever, lethargy, lameness, ataxia) in horses where ticks are endemic. But a Pennsylvania survey shows that infection with A. phagocytophilum and B. burgdorferi is not all that common even though ticks are commonly found in the state.

In that survey Thompson et al. analyzed blood samples collected from 271 horses whose veterinarians suspected tick-borne disease. The researchers used PCR to detect DNA from both bacteria and used the IDEXX SNAP 4Dx and an IFAT to detect antibodies.  

Key findings were:

• Researchers identified DNA for A. phagocytophilium in 7% of the horses. They did not find B. burgdorferi DNA in any horse;
• They detected antibodies to A. phagocytophilium and B. burgdorferi in 28.4% and 67.9% of horses, respectively;
• With IFAT they discovered antibody titers of 1:50 or more in 41.3% and 60.5% of horses for A. phagocytophilium and B. burgdorferi, respectively.

The high prevalence of antibodies to both bacteria in this survey shows that horses in Pennsylvania, where ticks are common, could have prolonged, repeated exposure to these pathogens (TheHorse.com/1118403).

“Again, though, simply identifying antibodies does not confirm that either of these bacteria are causing the disease. The presence of antibodies simply proves exposure to the bacteria,” says Foley.

The lack of B. burgdorferi DNA found in that study wasn’t surprising because the bacteria do not persist in the bloodstream for very long.

“For Lyme disease the bacteria can be sequestered in the joint, as well as any connective tissue, including kidney capsule, etc. For anaplasmosis, though, we do expect circulating blood to be PCR-positive during active infection,” says Foley. 

Identifying A. phagocytophilium DNA together with the lack of circulating antibodies in the bloodstream (the body hasn’t had time to produce them yet) and the presence of high fever or other clinical signs consistent with disease supports a diagnosis of anaplasmosis.

Emerging Tick-Borne Diseases

While Lyme, anaplasmosis, and piroplasmosis are the only three tick-borne diseases discussed in the U.S. for equids, surveys from other regions suggest Rickettsia spp and Ehrlichia spp might be clinically relevant in horses.

Therefore, Duncan et al. (2022) wanted to better understand the transmission risk of these tick-borne rickettsial disease agents.  In their study they tested ticks from horses residing in Oklahoma using PCR.

Additionally, they analyzed blood samples from horses both infested and not infested with ticks for antibodies to these bacteria.

They reported that illnesses caused by Rickettsia spp and Ehrlichia spp could be emerging tick-borne diseases in horses.

“We found that one-quarter of the ticks recovered from tick-infested horses contained DNA of Rickettsia spp, and R. amblyommatis was the most common species identified. This is part of the spotted fever group of bacteria, is transmitted by the lone star tick, and is currently considered nonpathogenic,” relays Duncan. “Ehrlichia spp were found far less commonly in ticks recovered from horses.”

In contrast, researchers did not find circulating antibodies for R. rickettsii in any of the study horses, but almost 30% of horses had antibodies for Ehrlichia spp.

“These results suggest there is a need to further explore the role of Rickettsia spp and Ehrlichia spp in equine health,” states Duncan.

The fact other diseases might also be transmitted by ticks isn’t surprising, considering ticks are known to transmit several different disease agents to humans in addition to Borrelia and Anaplasma. Examples include the agents of Rocky Mountain spotted fever, ehrlichiosis, tularemia, babesiosis, Colorado tick fever, and Powassan virus disease, among others.  

Take-Home Message

Some of the main takeaways from the current research are:

1. Many tick types can infest horses, but few are currently known to actually transmit disease to horses;
2. Tick ranges are expanding, so ticks are found in geographical ranges and at times of year they haven’t previously been found;
3. Anaplasmosis can occur commonly in certain geographic areas and should be considered as important a tick-borne disease as Lyme disease.

“If residing in a region with a heavy tick burden, be aware of practices to prevent tick-borne diseases including using regular tick control, screening annually with an antibody test, and performing thorough tick checks with proper removal,” advises Duncan.

This article first appeared in The Horse‘s Preventive Care Special Issue, which was distributed in June 2024. 

Enteroliths are a type of foreign body that can be found in horses’ intestines and are one possible cause of colic, or abdominal pain. Unlike sand or gravel, which horses ingest when they are grazing or eating outside, enteroliths develop when mineral deposits form in concentric layers around a central nidus, such as a piece of wire, small stone, twine, etc., in the large colon (the stretch of intestine between the cecum and the transverse colon). Horses can either have one enterolith (usually round and large) or multiple (often tetrahedral in shape, meaning they have angles or corners).

What Causes Enteroliths?

The cause behind enteroliths—and, especially, why some horses develop them but not others—is still not fully understood. Feeding high levels of alfalfa hay, particularly in California or other locations out west, has been associated with enterolith formation. Decreased turnout and limited access to pasture also have been linked to their development, possibly because of decreased intestinal motility or increased ingestion of alfalfa when stalled. Certain horse breeds (Arabians, Morgan horses, American Miniature horses, and Saddlebreds) have been shown to be more at risk for forming enteroliths.

Enteroliths cause problems when they get large enough that they begin to pass into the transverse or small colon. The diameter of the transverse and small colon is much smaller than the adjacent large colon, so the enteroliths become wedged. Once wedged they block food and gas from traveling out of the intestine, causing abdominal pain and signs of colic.

Some horses with enteroliths could have a history of recurrent colic (repeated colic episodes) due to enteroliths intermittently blocking the intestine and then other times allowing food and gas to pass normally. When the enterolith becomes completely wedged the horse will show signs of severe colic due to gas distension. If the enterolith is large enough and puts pressure on the intestine, it can cause necrosis of the intestinal wall in that area and lead to leakage of feces into the abdomen and secondary infection. In these cases horses show lethargy, decreased appetite, and fever, eventually progressing to signs of sepsis (a life-threatening systemic inflammatory response to infection) and shock. Due to how firmly enteroliths become lodged in the intestines, the treatment for enteroliths is always surgery.

Diagnosis

Veterinarians usually diagnose enteroliths at the time of colic surgery, when the colic signs do not respond to medical treatment, and/or the horse’s colon becomes distended with gas due to blockage by the enterolith. Abdominal X rays can be performed, but in most cases enteroliths are hidden by the large amount of tissue in the horse’s abdomen, making them difficult to detect.

Prevention

If your horse has had enteroliths before, veterinarians recommend taking preventive measures, because there is some evidence they can form again. In these cases, avoid feeding alfalfa and provide as much turnout on pasture as possible.

If at any point you see what looks like an enterolith in your horse’s manure, tell your veterinarian, because the presence of one enterolith (especially if it has a tetrahedral shape) often means there are more in your horse’s intestines. And if your horse shows signs of colic, you should always contact your veterinarian immediately.

Q. How long does it take for pasture grass sugar levels to drop after the sun goes down?

—Debra, Texas

A. The level of sugar in pasture grass varies due to several factors, including the weather, how stressed the grass is, its maturity, the time of year, and the time of day. As sun shines on pasture grass, the plants photosynthesize. This creates sugar stores the plan uses overnight to keep growing. Therefore, grasses tend to have higher sugar contents later in the day compared to earlier in the day.

Time Pasture Access Carefully

Generally, veterinarians and nutritionists recommend horses sensitive to sugar in pasture grass (such as those with insulin resistance, equine metabolic syndrome, or a history of laminitis) graze very early in the morning. It takes several hours after the sun sets for sugar levels to drop, so ideally try to avoid grazing before 3 a.m. And, because sugar levels start to build up again with sun exposure, it’s best to remove sensitive horses from pasture by about 10 a.m. If there’s significant cloud cover, you might be able to leave horses out a little longer, because photosynthesis (which relies on the sun) will be slower and therefore the amount of sugar will be lower.

One exception would be if the temperature drops below about 40°F overnight. At this temperature and below, the plants’ growth rate slow, which means stored sugars aren’t used up. As such, they’ll still be high in the early morning. In this situation, potentially at-risk horses should not have pasture access.

And, you must consider that some very sensitive horses might never be able to graze safely, while others can with careful grazing and pasture management. It all depends on the individual horse. Grazing muzzles are a very useful tool to help limit grass intake but still allow pasture access. Studies have shown that some muzzles can limit intake by as much as 80%.

Proper Pasture Management

Another important consideration is that most of the sugar in grasses tends to be in the bottom 3 to 4 inches of the plants. While it might be tempting to think that a very short, overgrazed pasture is safe because there’s “nothing out there,” such pastures present several risks—grasses are very stressed and only the lower inches of the plant are available, meaning these pastures can be very high in sugar.

As such, proper pasture management is very important to keep grasses from becoming stressed. This means horse owners need to properly fertilize and irrigate (if necessary) pastures.

It’s better for the plant and safer for the horse to stop grazing when the pasture has only about 3 to 4 inches of height left. This not only reduces sugar intake by your horse but also leaves some leaf for the plant so that it can regrow without having to dip in to root stores too heavily.

Take-Home Message

With an understanding of pasture grass metabolism and careful pasture and grazing management, many horses should be able to safely graze for at least part of the day. But, always consult your veterinarian or equine nutritionist before turning out your potentially sugar-sensitive horses on pasture.

Influenza in horses is typically caused by the H3N8 subtype of type A influenza virus. The H3N8 subtype circulates in equids worldwide and its infection often results in mild to severe respiratory disease. In addition to the H3N8 subtype, another influenza A subtype, H7N7, was also identified in horses in the 1950s. After a more than two-decade circulation in horses, H7N7 is believed to have become extinct, probably since 1979. In this regard, equids are unique in that only a single influenza virus, H3N8, is known to currently infect them. Humans and swine are infected by multiple subtypes of influenza A virus.

Current Knowledge About Highly Pathogenic Avian Influenza Virus (HPAI) H5N1 in Equids

Despite the consensus in the equine infectious disease research field that equids are not normally a host species of highly pathogenic avian influenza (HPAI) H5N1, very rare spillover events of HPAI H5N1 in equids over the past few decades occurred in donkeys and horses, respectively. In 2009, HPAI H5N1 was successfully isolated from diseased donkeys with influenza-like symptoms in Egypt. The antibodies to HPAI H5N1 were also detected in 27 out of 105 donkeys involved in this H5N1 outbreak. The combination of seroconversion and virus isolation data provides good evidence that equids are susceptible to infection by HPAI H5N1. Furthermore, a serosurveillance study in 2020 showed low level titers of H5 specific antibodies in wild asses (Equus hemonius hemonius) in Mongolia. Most recently, a comprehensive serosurveillance study of 2,160 equine blood samples collected from July to October 2021 from Mongolian horses, confirmed two samples positive for antibodies against H5N1 by using an array of different antibody assays. This latest serology data appears to continue a theme that equids are susceptible to HPAI H5N1 infection. Considering the low prevalence, it is very likely that HPAI H5N1 may not undergo an efficient transmission in horses, and horse-to-horse transmission may not occur.

Possibly, horses infected with HPAI H5N1 may not show any clinical symptoms. If so, despite the silent infection, HPAI H5N1 virus, when replicating in horses, may encounter seasonal H3N8 virus in the same horse. Such co-infections can create an environment to facilitate swapping genetic segments between the two subtypes and generate a new variant. Such a variant might have the transmissibility of the H3N8 parent and the virulence and novelty to the immune system of the H5N1 parent, which would enable the new virus to escape vaccination-mediated immunity, readily spread among horses, and could cause severe respiratory disease in horses and, potentially, in in-contact humans as well.

To protect equine health, HPAI H5N1 research and diagnosis in horses is critically needed so a potential threat of HPAI H5N1 can be identified before it can jump and spread in horses.

Rapid Response to HPAI H5N1’s Threat in U.S. Horses by the University of Kentucky Gluck Equine Research Center

Since late March 2024, the unprecedented spread of HPAI H5N1 in U.S. dairy cows raises critical questions about the virus’s potential to cross species barriers to infect and cause disease in other agricultural animals, including horses.

To investigate whether U.S. horses are susceptible to HPAI H5N1 infection, we and our collaborators across the country conducted a nationwide serosurveillance study involving 1,462 equine serum samples that were collected between July 2024 and February 2025. Samples were obtained from diverse geographic locations, with most samples from Minnesota, Nebraska, Kansas, Indiana and Kentucky, as well as 23 other states.

Using the IDEXX influenza nucleoprotein (NP) antibody competition ELISA, we found 653 samples (45%) tested positive for NP antibodies (produced by either H5N1 or H3N8). When these NP antibody positive samples were screened in the ID Screen influenza H5 antibody competition ELISA, we identified one sample positive for H5 antibodies. Further validation of the 653 NP antibody-positive samples with the hemagglutination inhibition (HI) assay showed that 641 out of 653 NP antibody-positive samples had detectable HI antibody titers against equine H3N8 virus, indicating these horses were previously vaccinated or infected with this subtype. Finally, none of the 653 NP antibody-positive equine serum samples were positive in the H5N1 HI assay whereas bovine H5N1-positive reference sera were successfully detected.

The current data from our study that is still in progress show that only one out of 1,462 equine serum samples is positive for antibodies to H5 antibodies, indicating that the chance of HPAI H5N1 spillover to U.S. horses is very low. Nevertheless, considering an extremely expanded list of host species that can be infected by HPAI H5N1 with fatal outcomes plus the fact that the HPAI H5N1 virus is mutating rapidly, scaling up H5N1 surveillance efforts in U.S. horses especially in regions where H5N1 has extensively circulated in bovines, is critically needed towards better understanding of equine susceptibility to HPAI H5N1 infection.

Editor’s note: This is an excerpt from Equine Disease Quarterly, Vol. 34, Issue 1, funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents. It was written by Feng Li, DVM, PhD, professor, William Robert Mills Chair of Equine Infectious Diseases at the University of Kentucky’s Gluck Equine Research Center, in Lexington.

Biosecurity measures remain a critical component to combating ‘strep throat for horses’

Teddy and the Chipmunks were brand-new additions at FarmHouse Fresh Sanctuary, in McKinney, Texas. The 15-month-old donkey and his three Miniature Horse friends were quarantined for the sanctuary’s standard 30-day period in the summer of 2023. On Day 29, feeling relieved that quarantine for Teddy and the Chipmunks was ending, the sanctuary’s team started removing the temporary fences that keep quarantined herds from touching noses with healthy resident animals.

On Day 30 the newbie herd started showing signs of equine strangles.

Strangles has been vexing horse owners since at least 1256. Caused by the bacterium Streptococcus equi, the common name “strangles” refers to the upper respiratory noise that is one of the disease’s more remarkable clinical signs. It ranks among the frequently encountered infectious diseases affecting horses.

Equine strangles is an old problem, but when it’s happening to your herd, it can feel dramatically new, changing your daily routines in an instant.

“We went on strict lockdown with them,” recalls Elise Khan, manager of the sanctuary. “Only one person would go in with them … once that person finished in the morning, they had to go upstairs and shower and change their clothes.”

Khan’s sanctuary team has been forthcoming online about the strangles outbreak. Khan says the organization’s mission to rescue animals from some of the worst situations puts her and her colleagues in a position to share information.

“It’s usually not somebody’s fault. No one would intentionally spread strangles,” Khan says. “I just feel (with) all these medical things, it would just be really comforting to me to have seen someone else go through it. And understand what to do and how to prevent it.”

‘Strep Throat for Horses’

Although it is caused by a different bacterium, “strep throat for horses” is a suitable analogy for strangles, says Ashley Boyle, DVM, Dipl. ACVIM. Boyle is an associate professor at the University of Pennsylvania New Bolton Center, in Kennett Square, teaching in the field service section. She has been researching strangles for 15 years and was the lead author on the American College of Veterinary Internal Medicine’s 2018 consensus statement regarding strangles.

But where humans can hoarsely complain about their sore throat, horses can’t articulate their discomfort.

“In horses, it gets further along before it’s recognized,” Boyle says.

The earliest sign your horse has strangles is a temperature spike. “A spike would just be an increased temperature from the normal range,” she says, which is typically 99-101.5 F. “Though sick horses are often 103 F or warmer, you should look for an increase in the horse’s normal recorded temperature.”

Other signs include a runny nose, difficulty swallowing, a “strangled” upper respiratory noise, not eating, swollen lymph nodes, or abscesses on the throat or jaw. Authors of the consensus statement report that the abscesses might rupture and drain externally or internally.

The strangles incubation period—the time from exposure to first indications of illness—can be three to 14 days, Boyle says. Once clinical signs start, they can last a few weeks.

While younger horses are more likely to be affected by strangles, S. equi can infect horses of any age. They can be exposed to the bacterium at shows, sales barns, or other places horses commingle.

PCR Testing: The Gold Standard for Equine Strangles

One of the newer developments in strangles detection and management is the use of a PCR (polymerase chain reaction) test. Now considered the “gold standard,” the PCR test can detect S. equi before a culture.

While it’s not “wrong” to test for strangles using a culture, Boyle says, it might miss the infection early on.

“If it’s early in the fever, you may not get a positive right away because they haven’t started shedding (the bacteria),” she says .

Veterinarians also need to test the correct area of the horse’s body. “They’ve heard us harp on checking the guttural pouches (blind-ended sacs on either side of the throat), but that’s actually more when you’re kind of looking to clean up the disease,” Boyle says. “The guttural pouches may not actually be positive early on in the disease.”

At the start, it might be better to get the sample from the nasopharynx (the cavity above the soft palate) via a nasopharyngeal wash or an aspirate of an enlarged lymph node.

“Those can be done with culture or PCR,” she adds. “But if you’re getting negatives and you’re still suspicious of strangles, you really should be checking with PCR.”

What You Need to Know About Guttural Pouches

If a horse has chondroids(firm balls of pus) in his guttural pouches, the S. equi is contagious. “That’s what makes the carriers and what makes the risk of infection keep going even if you have got all the clinical signs down in the herd,” explains Alberte Fridberg, DVM, of the University of Copenhagen’s Department of Veterinary and Animal Science and Ansager Equine Hospital, in Denmark. To look for chondroids in the guttural pouch, your veterinarian will use a scope and flush the area.

When a “persistent carrier” continues to shed the bacteria into common areas like water troughs, a strangles outbreak can seem to be waning, only to flare back up again, making the outbreak last longer.

Equine Strangles Vaccination Strategy

In the U.S. there are two strangles vaccines you need to know about, Boyle says. There is an intramuscular vaccine and an intranasal vaccine.

Both vaccines provide protection against S. equi. A benefit the intranasal vaccine offers is that it provides immunity at the location where bacteria enter the horse, Boyle says. Meanwhile an intramuscular vaccine given to the dam prior to parturition (birth) can provide protection to a suckling foal.

Strangvac, which is available in Europe but was still awaiting USDA approval as of November 2023, has the attention of Fridberg, who was still a veterinary student when strangles captured the attention of Denmark’s horse community during an outbreak. She was inspired to work on an article outlining strangles hygiene, which was ultimately published in 2023 in Equine Veterinary Education.

Fridberg says she finds Strangvac interesting because of its DIVA—differentiating infected from vaccinated animals—capabilities.

“We were missing that in some of the others,” Fridberg says. “That’s an important ability of a vaccine.”

Vaccine timing is important.

If your barn is in the middle of an outbreak, you’ll have to wait before vaccinating, says Boyle. That’s because some horses are hyper-responders and can develop purpura hemorrhagica (an immune-mediated inflammation of blood vessels causing swelling of the belly and limbs and bleeding noted on the gums) after the vaccine. For the same reason, you’ll need to be cautious about vaccinating horses known to have had strangles in the past. Your vet might recommend running a titer to check your horses’ immunity to be sure they aren’t at high risk of being hyper-responders.

Isolating the Sick Herd

When equine strangles strikes, put up the fences. Isolation is key because the bacteria spread through close contact and shared equipment.

“It’s easier said than done,” Boyle acknowledges. “And I so appreciate that. But it’s so, so important.”

Exactly how you’ll isolate your horses will depend on your facilities. On some farms, that might mean the barn becomes the sick ward, and the pastures are for horses without clinical signs. On other farms, that might mean turning a run-in shelter into a stall and adding a double fence perimeter to the shed so horses in the rest of the pasture can’t touch noses with the sick horse.

The team at FarmHouse Fresh Sanctuary, which faced two outbreaks in six months, designated one pasture for healthy horses. The pasture beside it was for sheep on one side and goats and donkeys on the other. The third pasture was for sick horses.

“None of them could touch noses,” Khan says. “The goats can’t get strangles, but let’s say (a sick horse) sneezed and a goat stepped in it and then walked over to a healthy horse. A healthy horse could get it (from coming in contact with the nasal discharge). So that’s why we got really strict.”

Checking Temps, Cleaning Buckets

Once you’ve established your quarantine area, look at hygiene considerations such as shared equipment, temperature checks, and personal protective equipment.

Shared water sources provide an opportunity for exposure to S. equi; each pasture and stall should have its own water source with no cross-contamination—don’t swap out buckets and don’t let a hose dip into the water of any bucket or trough and then dip it in the next.

You’ll need to clean, disinfect, and dry buckets and other shared materials. Don’t skip the drying process.

“The bacteria love wet environments,” Boyle says. “That’s been shown in studies.”

Also, remember the human element. You’re a possible disease “fomite.” The concern isn’t your snot; it’s the snot on your sleeve or slobber from a sick horse, much like the goat scenario Khan described (the goat could’ve acted as a fomite, too).

If you are managing a strangles outbreak, expect to do a lot of laundry. It will be up to you how you manage that; maybe you’ll elect to have personal protective equipment such as Tyvek suits. Maybe you’ll wear different clothing around different herds. Maybe you’ll have different personnel handle sick horses. You might also add a disinfecting foot bath station and hand sanitizer pumps.

For the most part, washing machines work well at killing off the bacteria. But beware of nylon halters. In a Swedish study, researchers found the bacteria survive on nylon halters even after going through the machine, Boyle says. It might be best to throw nylon halters away after sick horses wear them.

Though the long incubation period associated with strangles can be daunting, temperature checks are your best hope.

Catching a jump in temperature can allow you to move the horse to isolation before it starts shedding a lot of bacteria.

“That’s the way to stop the outbreak,” Boyle says.

She recommends twice-daily temperature checks for every horse on the farm during an outbreak, but stresses that making temperature checks a part of your regular horse care routine can make it easier to catch even illnesses besides strangles.

“Anyone who had a fever of over 102.5 degrees would go straight over to the quarantine,” Khan says of the farm’s second outbreak. The team would then clean and sanitize the horse’s stall and equipment. “We also took notes on their discharge from their nose because our vet tells us you’re basically looking for … banana pudding consistency.”

The long battle with strangles has Khan taking a different approach to biosecurity. She’s extended the quarantine period for new additions to 35 days and is adding a pharyngeal wash for testing to new horses’ standard care before being released into the herd.

If your horse comes down with strangles, your veterinarian might or might not recommend antibiotics. It will depend on how sick your horse is. Horses that get antibiotics for strangles might not develop strong immunity to S. equi and could be reinfected, per the 2018 consensus statement.

Take-Home Message

Regularly checking your horse’s temperature can help you catch equine strangles early.

Strategize now for how you will separate infected, exposed, and healthy animals on your property. Build or buy any infrastructure you might need, such as temporary fencing or extra water troughs. Finally, talk to your veterinarian about vaccinating your horse against strangles.

Further Reading

Fridberg, A., Adler, DMT, Jørgensen, M.G. & Olsen, R.H. (2023) The hygienic aspects in the management of strangles. Equine Veterinary Education, 35, 540–550. Available from: https://doi.org/10.1111/eve.13794.

Boyle AG, Timoney JF, Newton JR, Hines MT, Waller AS, Buchanan BR. Streptococcus equi Infections in Horses: Guidelines for Treatment, Control, and Prevention of Strangles-Revised Consensus Statement. J Vet Intern Med. 2018 Mar;32(2):633-647. doi: 10.1111/jvim.15043. Epub 2018 Feb 9. PMID: 29424487; PMCID: PMC5867011.

Greater awareness and ongoing research mean fewer foals are being born with this genetic skin condition

Attention stock horse owners: Have you heard of HERDA? For the past 20 years, learning about hereditary equine regional dermal asthenia (HERDA) has been a major goal of stock horse associations and HERDA researchers alike. Up to 3.8% of Quarter Horses—and specifically up to 28.3% of those in the cow horse population—are carriers for this debilitating genetic condition that causes horses’ skin to wrinkle, stretch, and slough. While HERDA horses can be maintained with specialized management, most affected animals are euthanized due to the impracticalities of that care, the inability to be ridden, and painful scarring.

With simple genetic testing, though, owners can find out if their animals are affected by or carriers of HERDA so they can make sound management and breeding decisions. As awareness increases, the industry should see fewer foals born with HERDA—and aim to eliminate clinical cases altogether.

How HERDA Happens

In 1978 scientists first described an unusual super-elastic skin condition and suspected it might have a hereditary link. They were right: In 2007 scientists discovered HERDA arises from a simple mutation on a gene called PPIB, located on Chromosome 1. If a foal inherits that same mutation from both parents, he or she will develop clinical signs of the disease, says Rebecca Bellone, PhD, Veterinary Genetics Laboratory director and a professor at the University of California, Davis.

Scientists traced the mutation back to its origin, a 1944 foundation Quarter Horse colt named Poco Bueno, who sired 405 registered foals. The stallion possessed mutated genetic codes for defective collagen processing. Collagens build connective tissues in skin as well as in cartilage, bones, tendons, ligaments, neurological membranes, and some other tissues. The most obvious effect of these defects is abnormally stretchy and wrinkly skin, with layers often detaching from each other so the skin peels away and sloughs. These gaping skin wounds—along with any other contact wounds—heal slowly and poorly, leaving disfiguring scars.

Owners might first notice frequent lacerations, cuts, or scrapes on young horses eventually diagnosed with HERDA, but the strongest clue appears when these animals are first saddled. At this point they often start to develop wounds along the back and neck. Ultraviolet rays from the sun seem to make the condition even worse, creating new lesions and exacerbating existing ones.

However, because horses have connective tissue throughout their bodies, they might also develop problems elsewhere, says Abby McElroy, DVM, MS, PhD candidate and researcher at the University of Massachusetts Chan Medical School, in Worcester. In particular, researchers know HERDA to be associated with an increased risk of corneal ulcers as well as abnormal heart valves, she says.

“If you have an affected horse, it’s obviously very serious for both the horse and the owner,” says Tammy Canida, registrar at the American Quarter Horse Association (AQHA), whose headquarters are in Amarillo, Texas. “The humane thing to do is put the horses down in most cases.”

It Just Takes Two Alleles

Early research in 2009 revealed 3-4% of Quarter Horses, Paint Horses, and other stock horses probably have the HERDA mutation. However, most of these horses show no signs of disease because they’re merely heterozygous carriers, meaning they have only one copy of the HERDA mutation.

Genetic material comes from both parents equally, as genes from the mother line up in the DNA on the chromosome with matching genes from the father, Bellone explains. Genes often exist in alternate forms, which are called alleles. If an individual gets a different allele from each parent for the same gene, he or she is heterozygous for that gene. If the alleles are the same, though, the individual is homozygous.

Because HERDA is recessive, horses must have acquired the mutated allele from both parents—meaning they’re homozygous—to show clinical signs, Bellone says. Therefore, horses that acquire the mutation from the dam or the sire alone are heterozygous and seem perfectly healthy. Meanwhile, they’re carrying the DNA for the disease. If heterozygous horses are bred to other heterozygous horses, their offspring could inherit the mutated allele from both parents, Bellone says. The resulting cross has a 25% chance of producing a homozygous individual—one with clinical HERDA.

Before 2007 breeders sometimes used trial and error to identify silent HERDA carriers in their breeding stock. But since the development of the DNA test for the HERDA allele, breeders have had a simple tool for recognizing carriers, Bellone says.

“That’s the thing about HERDA; it’s recessive,” she says. “So you can avoid producing an affected animal by knowing what the genotypes of the parents are.”

High-Performance HERDA Carriers

If there’s a DNA test for HERDA carriers, why wouldn’t we just sterilize all mutant-gene horses and eliminate the allele entirely?

The answer might be due to an ironic HERDA twist. As it turns out, there might be a link between a single HERDA allele and good athletic performance. In fact, three of today’s top cutting horse sires are HERDA carriers, says McElroy. So the demand for these genetic lines remains high. And that’s no secret to the AQHA.

“It seems to be in popular lineages that are performing well in the industry,” Canida says.

The reason for that link remains a mystery, says McElroy. “I think that’s a big question within the industry: Why are there so many super-performing carriers?” she says, adding that research is lacking.

Some people in the stock horse industry suspect the mutation might code for more joint mobility in heterozygous horses without causing the deleterious effects of the gene, she explains. “Maybe they have a little bit of the phenotype,” she says, a technical term for observable characteristics.

McElroy wonders if subtle changes in connective tissue might improve performance in athletes in general—both horse and human. “You look at swimmers and gymnasts, for example,” she says. “They’re obviously incredibly hypermobile. But they’re not ill. And for horses working in cutting and reining, that hypermobility would give them a huge athletic advantage.”

Even so, if the allele endows stock horses with a “superpower” that garners many winnings early in the horses’ careers but then leads to bone and joint conditions such as osteoarthritis later in life, it could pose a welfare issue, McElroy adds.

Thus far, scientists have neither studied these questions nor measured the degrees of equine or human joint hypermobility with regard to connective tissue quality. And there has been no research completed on bone and joint health specifically in HERDA carriers. “That’s something that really needs to be studied, in my opinion,” McElroy says. “At this point, it’s unclear if an athletic advantage truly exists. It’s also unclear if any perceived advantage comes from the HERDA mutation or another gene.”

DNA Testing: Quick, Easy, Affordable, and Important

With HERDA carriers’ successful performance careers and breeding popularity, genetic testing has never been more important, our sources say. “The number of carriers right now is astronomical,” McElroy says. “So people really need to make informed decisions before breeding.”

The AQHA and American Paint Horse Association (APHA) agree. To minimize the breeding of homozygous foals, the associations have teamed up with Bellone and other experts to create educational materials and offer easy instructions for owners to have their horses’ DNA tested. A simple HERDA DNA test requires a few strands of mane and costs $45 through the UC Davis Veterinary Genetics Laboratory, or $100 as part of the full AQHA/APHA genetic testing panel.

Since 2015 the AQHA has required that owners of all breeding stallions have their studs’ genetic HERDA information on file and accessible to mare owners. In 2018 the APHA followed suit. Foals can only be registered with the AQHA and APHA if their sires’ genetic information, including HERDA status, is on file with the association.

Being heterozygous doesn’t exclude the stallions from breeding, however. Canida explains that the goals of the test are purely informational. “We always recommend that mare owners ask stallion owners for the information that would impact their breeding choices,” she says. “But we also make it public information, so that they can always pull the record and see it on our files as well.”

The associations do not require owners to test broodmares, but they strongly encourage it—especially when considering breeding to a heterozygous stallion. “If mare owners are aware that the stallion they want to breed to is a carrier, then they need to test the mare to ensure that they don’t produce any affected animals,” Bellone says.

 “We feel that our goal is to educate the members about it so they can make the choices for their breeding barn,” says Canida. “We just want them to be aware of what a horse may or may not have.”

“And under current rules, it will not be eliminated,” she adds. The AQHA’s focus, she says, is on education so as “to avoid getting those (clinically) affected horses.”

Meanwhile, nonbreeding stock can also undergo DNA testing if their owners suspect they’re homozygous or even heterozygous for HERDA, or if they’re just curious, our sources say. Both the AQHA and APHA websites provide educational tools that help owners understand DNA test results and how to manage their horses accordingly.

Importantly, awareness—even of the tests themselves—remains key, stresses Bellone. “If the genetic test exists, but people aren’t using it, it’s not helping,” she says.

Managing (and Surviving) HERDA

While the main goal is preventing the birth of any homozygous foals, the harsh reality is such births persist, our sources say. Our sources say most affected adult horses end up being euthanized, some are shipped for slaughter, and a few are rescued by nonprofit organizations. Some homozygous mares serve as embryo transfer recipient mares. Occasionally, owners keep their own homozygous foals as well-protected pets. McElroy says she recalls the case of a homozygous horse that successfully worked cattle for eight years—although it’s possible the horse had, for reasons unknown, a milder form of the disease.

If their quality of life permits it, HERDA horses could be kept in indoor conditions during daytime hours to prevent sun rays from breaking down collagen, she says. Owners would have to ensure the environment is low-risk for contact injuries—even rubbing against surfaces—and for insect bites. “There are owners who have kept these horses going for many years, keeping them inside during the day, turned out at night with intensive fly management, staying away from … anything that’s going to traumatize the skin,” McElroy says.

Management methods for similar connective tissue disorders in humans and smaller animals have progressed in recent years because these individuals’ environments can be more easily controlled. Unfortunately, that’s not the case for horses. “We just don’t know much about keeping these horses going longer,” she says.

“At this point, we don’t have a lot of therapies or treatments,” McElroy says. “It would really just be intensive management.”

HERDA on the Horizon

In the past two decades, HERDA researchers have mostly studied the condition’s effects on the skin, but they’ve started looking into its effects elsewhere in the horse’s body. For example, homozygous horses have thinner corneas with more frequent ulcers, and they have weakened heart valves.

“Collagen is everywhere, so it affects every bodily system,” says McElroy, who studies HERDA as an equine model for Ehlers-Danlos syndrome—the general HERDA analog affecting humans, rabbits, cats, dogs, cattle, sheep, and mink. “There’s a lot we don’t know about. Do they have bone fragility? What’s going on with their GI tract? Are they more likely to colic? Are they more likely to have bladder ruptures as foals?” Her own work has focused on the nervous system and confirms—like in humans with Ehlers-Danlos Syndrome—HERDA horses have abnormal spinal cord regions in the sacrum area, although the physical implications remain unclear.

Scientists are also considering whether HERDA affects some horses more severely than others—with some, like the exceptional HERDA working cow horse, having such mild disease it might even go unnoticed. “For me the question has always been, ‘Are there some underlying genetics that can protect some horses?’ ” Bellone says. “And also, ‘Is there any hope of testing for something like that, or doing any kind of research on it?’ ” To her knowledge, at this time, there is not.

An upcoming research area for such diseases is gene therapy, which essentially involves injecting the healthy allele via a viruslike vector into newborns, effectively replacing the bad allele, McElroy says. Better yet, gene therapy could start after genetic testing of the embryo. While progress is underway for humans, the astronomical price of such therapy—reaching seven figures—is likely to preclude its commercial use in horses. “It would be more like on a research basis,” she says, adding that costs might drop over time and especially with prenatal treatment.

Meanwhile, scientists and associations are continuing to focus on awareness, making sure owners understand what HERDA is and how to prevent it through DNA testing and wise breeding. Efforts so far have been fruitful, McElroy adds, with a drop in the number of homozygous foals born.

Whether the incidence of the allele itself is dropping remains hard to say, notes Bellone. With the steep increase in testing, it’s difficult to compare today’s rates with those from the mere hundreds of horses tested 15 years ago. Even so, ongoing analyses suggest there’s a trend toward a drop in allele frequency, she explains.

“We need to continue that push for education and make sure that people really understand the genetics of a recessive disease, and make sure they understand the risk of carrier-to-carrier matings,” McElroy says.

Take-Home Message

As scientists progress in their understanding of HERDA, so must the owners and breeders managing and producing the horses that carry the alleles responsible for this recessive disorder. With improved awareness and ongoing investigation into the whole-body effects of this disease, the industry is striving toward prevention and—potentially in the distant future—a hope for therapeutic management.

Over the last two decades, West Nile virus (WNV), an orthoflavivirus transmitted by mosquitoes, has become endemic on all continents except Antarctic and continues to be a major threat to the health and well-being of both horses and humans. The virus had an explosive emergence in North America in 1999, followed by rapid expansion throughout the U.S. and parts of Canada over the first five years, which resulted in often catastrophic disease in over 25,000 U.S. horses. With the rapid deployment of vaccines, the U.S. equine caseload decreased dramatically by 2006.  

Once established in a new area, reported cases in humans and horses, depending on vaccine status, will occur yearly but can vary in intensity from year to year. The virus can also cause explosive outbreaks in new locations or among those that have only experienced sporadic cases.  

While most mosquito borne viruses are typically associated with tropical or subtropical climates with high precipitation, WNV is endemic in a variety of climates, including temperate, continental and semi-arid areas. The continental U.S. and Europe are two great illustrative examples of the adaptability of this wide-ranging virus. During the last 10 years, 2,484 cases of equine WNV were reported in 46 U.S. states. Climate did not appear to be an issue since the states reporting the highest number of cases of WNV infection (Texas, Pennsylvania, California, Colorado, Utah and Montana) spanned all six U.S. National Oceanic and Atmospheric Administration defined climate regions. In Europe, most WNV activity in equids was initially reported in regions around the Mediterranean basin, however, during the past two decades, WNV activity was reported in more central and northern countries and regions such as Western France (Landes), Eastern Austria (Vienna), Hungary, and Northeastern Germany (Berlin). In 2024, a spike in the number of cases occurred with 494 affected premises reported in 10 countries, representing a 50% rise in reported equine cases over the two previous years. Northern Germany had the highest number of reported cases, approximately 200, with disease occurring in two federal states where activity had not been previously reported. There were 55 affected premises, typically with one or two cases, reported in Austria, a country in which the previous highest case count was four in 2019.  

WNV outbreaks are not confined to North America and Europe. Outbreaks have been reported in Central and South America, the Middle East and Australia. Australia is home to WNV lineage denoted as Kunjin virus, or WNV subtype 1b, which underwent a change in virulence resulting in a severe WNV outbreak in 2011 affecting over 1,000 horses.  

Nine lineages are now recognized with at least three (Lineage 1a, L1b and L2) associated with neurological disease in horses and cause similar clinical signs and pathology. When data is analyzed across multiple studies, mortality is about 30-40% for all lineages. Neurological disease, often with severe outcomes, remains the primary clinical presentation in the nonvaccinated horse.  

Contrary to observations for other viral epidemics, the virulence of this virus has not declined over time. West Nile fever is not recognized in the horse and all clinical manifestations observed are neurological. Affected horses had one or more neurological abnormalities consisting of changes in mentation (30%), locomotion (70%) and/or cranial nerve deficits. A common feature (approximately 80%) of WNV in horses was the presence of muscle tremors or fasciculations. In an analysis of pooled data from 14 studies (2,182 horses), approximately 30% of horses became recumbent necessitating euthanasia for humane reasons.  

Many studies examined risk factors for disease, including intrinsic factors such as age, sex or breed predilection with pooled analysis demonstrating no inherent bias. While early studies suggested an increased risk of mortality for older horses associated with underlying health issues, in fact all unvaccinated horses less than 1 year old infected with WNV died. Multiple extrinsic factors such as hair coat, housing, use of fans, etc. have been analyzed and were found equivocal to disease. Vaccination overrides all risk factors in terms of effect on susceptibility to disease.  

With no specific antiviral therapies, vaccination is the only intervention that successfully prevents severe neurological disease in the horse. Currently all marketed vaccines have comparable efficacy (over 90%) against known lineages that infect horses, and vaccines are marketed in North America, the United Kingdom and Europe. The American Association of Equine Practitioners identifies WNV vaccination a core component, which indicates that horses should be immunized annually to prevent disease. Vaccination against WNV is considered a ‘best practice’ under the guidelines provided by The Equine Infectious Disease Surveillance of the United Kingdom. While annual boosters are recommended, horses are not fully protected unless the initial immunization consists of two injections given four weeks apart. Foals must receive an additional booster 10 to 12 months prior to the next mosquito season or eight weeks after the second dose.  

With continuous expansion of this virus within and beyond an established endemic area, coupled with (international) travel of horses in and out of these areas, veterinarians and owners should consider all horses irrespective of location and climate at risk for WNV disease if not vaccinated. 

Editor’s note: This is an excerpt from Equine Disease Quarterly, Vol. 34, Issue 1, funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents. It was written by Maureen T. Long, DVM, PhD, Dipl. ACVIM, emeritus professor at the University of Florida’s College of Veterinary Medicine, in Gainesville. 

Age can complicate managing already tricky metabolic diseases in horses

Metabolic diseases, including both insulin dysregulation (ID) and pituitary pars intermedia dysfunction (PPID, previously known as equine Cushing’s disease) occur commonly in horses. Estimates indicate approximately 20% of horses 15 or older have PPID, while the prevalence of horses with ID or a combination of ID/PPID remains unknown.

The most important pathological—involving disease or damage—condition of both ID and PPID horses is laminitis, referred to in this setting as endocrinopathic laminitis or hyperinsulinemia-associated laminitis (HAL). As with other forms of laminitis, horses with HAL suffer extreme pain, lameness, and compromised quality of life.

Rather than delving into the clinical signs and diagnosis of ID and PPID, we’ll move beyond the basics in this article, focusing on best practices for managing aging horses with ID, PPID, or both. The key areas of management we’ll describe include diet and exercise tailored to aged horses, as well as medications. Special consideration also goes to managing older horses with osteoarthritis (OA) and understanding end-of-life care.   

Feeding Aging Metabolic Horses

Without a doubt, diet is the cornerstone of managing metabolic horses to decrease postprandial (after meals) hyperinsulinemia, even if the horse is not overweight.

“It is crucial to limit nonstructural carbohydrates, which are the sugar and starch components of the diet, in horses with ID to control postprandial hyperinsulinemia,” says Erica Macon, MS, PAS, PhD, of the Department of Animal Science at Texas A&M University’s College of Agriculture and Life Sciences, in College Station.

Scientists derived original recommendations of feeding commercialized concentrates and hay with less than 12% NSC from research in healthy horses, and they theorized this level would be safer for horses with metabolic disease. Since then, Macon and other nutritionists have recommended low-NSC hays, decreased pasture access, and ration balancers.

“However, it’s important to recognize that individual horses may have different insulin responses to the same diet,” says Tania Sundra, BSc (Hons), BVMS, MANZCVS (equine medicine), of Avon Ridge Equine Veterinary Services, in Brigadoon, WA, Australia. “Factors such as genetics and the gastrointestinal microbiome likely play a role in this interhorse variability, though this has not been fully elucidated. While some sources suggest a stricter threshold of 10% NSC, the 12% guideline is generally considered appropriate for most horses. Monitoring your horse’s insulin levels and adjusting the diet accordingly remains the best approach to managing horses with ID.”

Macon also points out that “nutritionists are trying to move away from percent-NSC basis. We now recommend that horses with hyperinsulinemia are limited to 0.1-0.15 grams NSC/kilogram body weight (BW) per meal.”

Forage should form the basis of the diet, and horses in good body condition should be offered 2% forage BW. However, if horses need to lose weight this might need to decrease to 1.75% BW or even 1.5% BW.

“But no lower than 1.5% BW, otherwise you jeopardize the integrity of the hindgut,” Macon says. The hindgut refers to the cecum and large colon (or large intestine).

Sundra adds, “Ideally the forage will be split into multiple small meals to mimic a more natural feeding pattern and help reduce the postprandial insulin response by preventing large spikes in insulin that can occur with larger meals.”

Although some producers do have their hay analyzed, the technique might not be ideal or accurate, says Macon. But having a laboratory with an expansive database analyze hay is a crucial step in managing insulin-dysregulated horses, and both she and Sundra recommend it.

“Owners only need to test one batch at a time (i.e., same cutting or load of hay), not each bale,” says Macon.

Lean senior metabolic horses are much more difficult to manage than overweight animals because they need calories to maintain or put on weight, but they still need lower NSC concentrations.

“Most senior horses will experience sarcopenia (progressive loss of skeletal muscle mass), especially those with PPID,” Macon says. “We therefore need to feed quality, bioavailable amino acids. Ration balancers work very well for this.”

Sundra agrees, saying a senior metabolic horse’s diet needs to address both muscle maintenance and safe calorie intake. Her tips include:

• Manufacturers often formulate senior-horse-specific feeds to provide higher-quality protein (including the amino acid lysine) to help combat age-related muscle loss/sarcopenia;
• Calories (energy) should come from safe, low-NSC sources, such as beet pulp without molasses, fats, and oils (e.g., rice bran or flaxseed oil) rather than high-starch grains; and
• Forage should still be the foundation of the diet, with an emphasis on low-NSC hay or a soaked hay to reduce NSC content (be sure to discard the soaking water so the horse doesn’t consume it).

Including Exercise in Treatment

For horses with metabolic issues, especially those that are overweight, exercise should be a fundamental feature of management alongside nutrition. In fact, a combination of diet and exercise resulted in a greater improvement in insulin sensitivity in obese ponies compared to diet restriction alone (Bamford et al., 2019).

According to a survey by Herbst et al. (2024) of 2,700 owners of aged horses, 79% engaged in little structured exercise.

“I was involved in this project and, even though we know exercise is beneficial, the reality is that getting owners onboard is extremely challenging,” says Macon.

The following exercise recommendations come from the European College of Equine Internal Medicine (ECEIM) consensus statement on EMS written by Durham et al. (2019, tinyurl.com/yjnjn4dw):

In nonlaminitic ID horses, minimum recommendations include low-to-moderate-intensity exercise to achieve heart rates of 130 to 170 bpm for more than 30 minutes, more than five times a week;

In previously laminitic horses with recovered and stable hoof lamellae, minimum exercise recommendations involve low-intensity exercise on a soft surface to achieve heart rates of 110 to 150 bpm for more than 30 minutes, more than three times per week, while riders/trainers carefully monitor for signs of lameness.

However, in addition to owner commitment and the laminitic discomfort that limits a horse’s ability to exercise, OA might also contribute.

Arthritic Metabolic Horse Exercise

Among owners caring for aging horses, even without metabolic conditions, OA is a leading concern. In a recent survey of 2,717 U.S. horse owners, researchers found that 30% of horses had veterinarian-diagnosed OA (Herbst et al., 2024). Common methods of managing OA include administering non-steroidal anti-inflammatory drugs (NSAIDs) such as phenylbutazone or “Bute” or intermittently giving intra-articular (IA) steroids such as betamethasone.

Medication Effects on EMS Horses

François-René Bertin, DVM, PhD, an associate professor in large animal internal medicine from the Department of Veterinary Clinical Sciences at Purdue University College of Veterinary Medicine, in West Lafayette, Indiana, recently demonstrated that phenylbutazone does not increase insulin secretion in ID horses (Kemp et al., 2024).

Hypothesizing that NSAIDs might increase insulin secretion through prosteglandin E2 (PGE2, principal mediator of inflammation in diseases such as osteoarthritis) inhibition in horses, Bertin et al. administered either phenylbutazone intravenously for nine consecutive days or a saline placebo to nine healthy horses and seven horses diagnosed with ID. Horses then underwent testing to measure circulating insulin and glucose levels and, unlike in humans, insulin concentration decreased.

This suggests that in horses with ID, Bute decreases ID-associated inflammation and improves tissue insulin sensitivity, (crucial for glucose uptake and metabolism) leading to decreased insulin secretion.

“Those effects are rather mild but give us some insight about the role of inflammation in the development of ID,” says Bertin. “These data should not, however, suggest that phenylbutazone is a safe long-term treatment for (horses with) HAL. Instead, phenylbutazone can provide short-term pain relief without increasing insulin in metabolic horses with HAL.” 

Studies of IA corticosteroids do not bring equally good news. Instead, researchers widely report potentially harmful effects of corticosteroids even after a single joint injection. For example, in multiple studies, authors report significant increases in circulating insulin and glucose concentration following a single IA dose of triamcinolone, a commonly administered steroid for managing OA in horses.

Page and colleagues conducted a pilot study to determine the metabolic effects of the corticosteroid betamethasone in five healthy and three ID horses (Page et al., 2025). They injected 9 milligrams of betamethasone into each horse’s front fetlock joint before performing an oral sugar test and measuring adrenocorticotropin—ACTH, a hormone the pituitary gland releases—and cortisol levels (excessive ACTH amplifies cortisol secretion from the adrenals).

They found IA betamethasone had systemic effects on the horses, suppressing both ACTH and cortisol. 

“While it is unknown whether the temporary suppression of ACTH and cortisol is of significant detriment to horses, cortisol is an important hormone in stressful situations, so that raises the potential that these horses may not be able to respond properly to those situations,” Page explains. “There is also the concern that these drugs may cause a temporary immunosuppression, although work to better understand this is ongoing.

“While we were not able to make very many specific conclusions in this preliminary study, we did note that the metabolic effects of betamethasone were similar, albeit shorter lasting and smaller, than triamcinolone,” he adds. “As a result, we again recommended continued caution using corticosteroids in ID and/or laminitis-prone horses.”

Page says the group plans to expand on their work into other IA medications and larger groups of ID horses, given the importance of targeted treatment options for this horse demographic. In the meantime, for those looking for a noncorticosteroid alternative, Page and colleagues demonstrated that autologous protein solution (APS) administered IA did not exert any metabolic effects compared to triamcinolone in healthy horses, suggesting it could be a potential treatment option in ID horses (TheHorse.com/1132877).

Medications to Consider

Pergolide Veterinarians recommend treating PPID horses with pergolide. The 2023 Equine Endocrinology Group reports that clinicians should start with an initial pergolide dose of 2 micrograms/kg (0.5 mg for a 250 kg pony and 1.0 mg for a 500 kg horse) once daily (tinyurl.com/2a9a2wh7).

Practitioners might also consider prescribing cabergoline, a human drug Cabergoline used to treat different types of medical problems that occur when the body produces too much of the hormone prolactin.

Sodium-Glucose Cotransporter-2 Inhibitors (SGLT-2is) When indicated, SGLT-2is might benefit horses with ID. These medications increase urinary excretion of glucose, which in turn decreases the amount of glucose in the circulation. As a result, horses need less insulin to control blood sugar levels. Some published studies support the off-label use of various SLGT-2is, including canagliflozin, ertugliflozin, and velagliflozin, in horses.

“While SGLT-2is can be a valuable tool in managing severe hyperinsulinemia, these medications are typically reserved for cases that have failed to respond to dietary interventions or for severely affected horses where immediate insulin reduction is necessary,” says Sundra. 

She went on to describe four scenarios where she recommends an SGLT2i:

1. Short-term during transition to a low-nonstructural-carbohydrate diet;
2. Emergency use following accidental overconsumption of NSC-rich feed;
3. Preventively prior to corticosteroid administration; and
4. When managing chronic, severe, resistant equine cases.

“Some horses remain persistently hyperinsulinemic despite strict dietary control,” Sundra says. “In these refractory cases, an SGLT2i may be considered for longer-term management to maintain lower insulin levels and reduce the risk of laminitis. However, this should be closely monitored by a veterinarian, as long-term effects and optimal dosing strategies are still under investigation.”

Veterinarians prescribe these medications off label, relying primarily on clinical experiences for evidence of their effectiveness.

“In Australia and the U.K., ertugliflozin is most commonly used in clinical practice,” says Sundra. “The case studies we have published used a dose of 0.05 mg/kg once daily, but some animals might be controlled on lower doses.

“SGLT-2is should be carefully considered within the context of individual risk factors, and their administration should always be part of a comprehensive management plan that prioritizes nutrition, exercise, and overall metabolic health,” she adds.

Combining Pergolide, SGLT-2is Recall that many horses with insulin dysregulation also have PPID and could therefore need treatment for both conditions.

“There are no known interactions between the SGLT-2i ertugliflozin and dopamine agonists like pergolide or extended-release cabergoline,” Sundra explains. “However, it’s worthwhile mentioning that dopamine agonists can sometimes cause a temporary decrease in appetite, so if a horse is already on ertugliflozin and pergolide or extended-release cabergoline is being introduced, I always advise stopping the ertugliflozin for a few days to ensure the horse continues eating to reduce the risk of hyperlipemia (elevated lipid concentrations in the bloodstream).”

Critically Assessing Quality of Life

As one can imagine, it’s not easy managing chronic laminitis in addition to other age-related co-morbidities such as OA. Researchers have reported the prognosis for PPID is poor, with only 50% of horses surviving more than 4.5 years after being diagnosed (Johnston et al., 2025).

As difficult as end-of-life care can be to discuss, preplanning avoids last-minute emergencies and allows your older horses to live their final days with dignity. To successfully navigate the end-of-life phase, owners need to be able to critically assess their horses’ quality of life. In other species various quality-of-life tools are available. In dogs, for example, “The HHHHHMM Scale” (tinyurl.com/3drssxd2) takes the animals’ pain, happiness, mobility, and day-to-day engagement into consideration.

No comparable scale yet exists for horses, but in 2022 Long et al. collected data from 14 published studies on equine welfare that might help owners make informed decisions toward the end of their horses’ lives. They recommend that quality-of-life assessment includes both behavioral parameters to assess the horse’s mental state in addition to the physical state. They further suggest evaluating behavioral and physical parameters over time, stating that assessing quality of life remains an ongoing process, not a single event. 

Ideally, owners partner with their veterinarians to make this delicate decision together, ensuring horses’ best interest is always paramount, regardless of the emotional attachments.

Take-Home Message

Sundra says the greatest challenge in managing aging horses is ensuring a good quality of life while addressing the complexities of aging-related conditions.

“Chronic diseases occurring in older horses, such as OA, PPID, and ID, require proactive management to prevent pain, mobility issues, and laminitis,” she says. 

Nutrition and preventive care play a critical role in managing these diseases in our older horse populations. Early detection and intervention for conditions such as PPID and ID can significantly improve long-term treatment outcomes. “A precision-medicine approach, tailoring care to each horse’s needs, is key, as a one-size-fits-all strategy is unlikely to be effective,” says Sundra. 

This article is from the Older Horse 2025 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.

The Kester News Hour at the annual American Association of Equine Practitioners Convention highlight key advancements in equine research worldwide. In 2024’s edition Carrie Finno, DVM, PhD, Dipl. ACVIM, professor of veterinary genetics and the Gregory L. Ferraro Endowed Director of the Center for Equine Health at the University of California, Davis, and Katie Seabaugh, DVM, Dipl. ACVS, ACVSMR, associate professor of equine sports medicine and rehabilitation at Colorado State University, in Fort Collins, shared their top picks from recent studies in their areas of practice interest.

Studying Graying Speed and Melanoma in Horses

Finno began with research by Rubin et al. (2024), in which researchers identified a genetic variation in horses that determines their greying speed and melanoma incidence.

“Graying is caused by a duplication of a 4.6 kb (kilobase, a unit of measurement used to help designate the length of DNA or RNA) intronic sequence in syntaxin 17 (STX17),” said Finno. “If horses have one copy of the variant, then they are not gray. Gray horses with two copies of STX17 gray slowly and have lower rates of melanoma but, if a horse has three copies, then they are the fast-graying horses linked with melanoma.”

For example, if a gray mare has the genes G3/G1 and the gray stallion is G3/G1, then the foal could be G3/G3, meaning he or she will gray very fast and has a higher likelihood of developing melanoma. The results could lead not only to better identification of horses likely to gray early or pass on gray-with-age genes but also to a better understanding of how the mutation affects horses’ health.

Detecting Atrial Fibrillation in Horses

In the second study Finno covered (Vernemmen et al., 2024), researchers described a method for veterinarians to detect atrial fibrillation in horses using an implantable loop recorder (ILR).

The ILRs can be placed under the skin in the left lateral thorax overlying the heart, said Finno. Practitioners use these to detect arrhythmias as a possible cause of collapse, poor performance, or monitor for atrial fibrillation (AF) recurrence in a research setting. The device can now collect information and email the clinician, improving the speed with which AF can be identified.

“Be aware that some false positives can be a result of bradycardia (when the heart beats slower than normal) rather than AF because it is a human product,” said Finno. “And we need to appreciate that AF is likely genetic.”

Identifying A Cause of Neck Pain in Horses

Seabaugh presented a study (Hendersen et al., 2024) in which researchers described the incidence of neck pain without neurologic disease in horses with transposition of the ventral lamina from C6 to C7 of the cervical vertebrae.  

“The ventral lamina is part of the transverse process, and this ventral aspect of C6 can move to the C7 vertebra,” said Seabaugh. “When located on C6, the longus colli muscle attaches to the ventral lamina, which is a cervical flexor. Movement of the transverse process likely affects the biomechanics of the neck.”

In the retrospective study, researchers looked at radiographs taken from 2020 to 2022, including a total of 135 horses. Reasons for radiographs included routine neurologic exam, neck pain, and performance-related behavior changes.

Key findings were:

1. The researchers saw transposition in 20% of the horses that was not significantly associated with a final diagnosis, meaning an equal number of horses with or without the transposition fell into each diagnosis; and
2. Transposition was more common in horses that demonstrated pain during palpation of the neck (31%) than those without pain (18%).

Additionally, 63% (17 out of 27) of the horses with transposition were Warmbloods.

Prevalence of Neck Pathology in Warmblood Horses

Looking at Warmbloods more closely, Seabaugh presented a second study (Sue Dyson et al., 2024) where researchers described the prevalence of C6 and C7 transposition in the breed.

“This study included only Warmbloods: 127 controls and 96 horses with neurologic abnormalities, neck pain or stiffness, or neck-related forelimb lameness,” Seabaugh said. The researchers found 24.2% of horses had C6 and C7 transposition. Horses without neurologic issues (the controls) were more likely to have this variation than those with neurologic abnormalities.

“The conclusion from both studies was that there is no association between C6/7 transposition and neurologic disease, and it is just a variant occurring in up to one-quarter of all horses,” said Seabaugh.

Updated ACVIM EHV Consensus Statement

Finno broke down the updated ACVIM consensus statement for equine herpesvirus (Lunn et al., 2024) for the audience.

Three key takeaways from the new guidelines included:

1. Researchers have seen minimal evidence that the vaccine protects horses against equine herpesvirus-1 infection, but they still recommend vaccinating.
2. Pharmacological treatments have minimal effect (except valacyclovir if administered in advance).
3. In large outbreaks nasal swabbing typically suffices for diagnosing affected horses; however, when abortion occurs on the premises, veterinarians need to test blood samples.

In a study following the herpesvirus outbreak in Valencia, Spain, “Sixty-eight percent of horses with neurologic disease returned to exercise, and over half returned to full performance,” said Finno. “But the less ataxic they were on presentation, the more likely they were to fully recover. If there was urinary and vascular compromise, then they were more likely to be euthanized.”

Spring has officially sprung in Kentucky with flowers in full bloom and the horses off to the races! While we may be excited to get outdoors and enjoy the sunshine after a long winter, the warm weather also draws out other critters … ticks. Often overlooked compared to mosquito-borne pathogens, ticks are capable vectors of several equine diseases and can cause adverse effects ranging from local irritation to acute and chronic disease. Proactive tick management is an essential component of equine preventive care, particularly as many regions continue to report increased numbers of tick bites and changes in tick species distributions.  

In the United States, notable tick-borne diseases affecting horses include:  

• Equine Granulocytic Anaplasmosis (Anaplasma phagocytophilum) – most commonly observed signs of infection include fever, lethargy, limb edema and ataxia. In equines, A. phagocytophilum is most commonly transmitted by the blacklegged tick (Ixodes scapularis) in the Northeast, Midwest and parts of the Southeast, but may be transmissible by the Western blacklegged tick (Ixodes pacificus) on the West Coast.  

• Lyme Disease (Borrelia burgdorferi) – although horses are less susceptible than dogs or humans infection can result in chronic weight loss, shifting lameness, behavioral changes, and neurological signs. This disease can be difficult to diagnose in equines, as a positive blood test indicates exposure to the pathogen but not necessarily current disease status. Lyme Disease is also transmitted by I. scapularis.  

• Equine Piroplasmosis (EP) – caused by Babesia caballi and Theileria equi. This disease is reportable in the mainland U.S., but endemic in Puerto Rico and the U.S. Virgin Islands. Transmission can occur through tick bites (most commonly from Dermacentor or Rhipicephalus spp.), but most U.S. outbreaks or reports of disease are associated with iatrogenic transmission from contaminated equipment during unsanctioned racing events or through illegal importation of infected Quarter Horse racehorses.  

• Tularemia (Francisella tularensis) – a rare tick-borne zoonotic disease in horses, associated with Dermacentor spp. and Amblyomma spp. ticks. This pathogen can be transmitted through bites from fleas and flies and through contaminated water sources, but is most commonly associated with tick bites. While rare in horses, it is of veterinary and public health significance due to its ability to persist in the environment, multiple modes of transmission and zoonotic disease potential.  

• Tick Paralysis and Hypersensitivity – Toxins in tick saliva may cause neuromuscular dysfunction or localized inflammatory responses in sensitive animals.  

Emerging Tick Species: Asian Longhorned Tick  

The Asian longhorned tick (Haemaphysalis longicornis) is an invasive species that has been detected in numerous U.S. states along the East Coast and Appalachian Mountains, including Kentucky, where it has been detected on wildlife, cattle, equines, dogs and people.  

• It reproduces asexually via parthenogenesis, enabling rapid population growth and large infestations, particularly on livestock.  

• This tick has been documented on horses in the U.S., although no confirmed cases of equine disease have been associated with it.  

• Internationally, H. longicornis can transmit pathogens of veterinary and medical concern, causing diseases such as anaplasmosis, babesiosis, ehrlichiosis, theileriosis and rickettsiosis.  

• Its ability to cause anemia and death in cattle raises concern for similar effects in heavily infested horses, particularly if infestations go unnoticed, though such cases have not yet been reported.  

• As horses can develop hypersensitivity reactions to tick and other arthropod bites, even mild infestations of H. longicornis could exacerbate stress, pruritus and allergic dermatitis, affecting welfare and performance even in the absence of pathogen transmission. 

Most Common Equine-Associated Tick Species in the U.S.  

• Amblyomma americanum (lone star tick)  

• Amblyomma maculatum (Gulf Coast tick)  

• Amblyomma mixtum (Cayenne tick)  

• Dermacentor albipictus (winter tick)  

• Dermacentor andersoni (Rocky Mountain wood tick)  

• Dermacentor variabilis (American dog tick)  

• Haemaphysalis longicornis (Asian longhorned tick)  

• Ixodes scapularis (blacklegged tick)  

Integrated Tick Prevention and Property Management  

Most tick species tend to prefer habitats with shade, moisture and vegetation, including wooded edges, brush and tall grasses commonly found on or adjacent to horse properties, or along trail riding locations. To reduce equine tick exposure, there are environmental, behavioral and chemical strategies available to reduce the number of ticks on the property and reduce equine exposure to areas where ticks may be more common. This can include pasture and property management to reduce areas that are more likely to harbor ticks and reduce wildlife from bringing ticks onto the property. Integrated management also includes on-animal prevention strategies to reduce ticks from attaching to animals and removing ticks quickly when they do attach to animals.  

Pasture and Property Management  

• Mow and maintain pastures frequently to reduce habitat more likely to harbor ticks.  

• Create buffer zones between wooded or brushy areas and paddocks.  

• Remove brush, leaf litter and overgrown field margins.  

• Exclude wildlife (e.g., deer, raccoons) via fencing or deterrents to reduce tick introduction and movement of disease-causing pathogens.  

• Control rodents through exclusion and secure feed storage; rodents serve as reservoirs for immature ticks and several tick-borne pathogens.  

On-Horse Prevention  

• Perform daily tick checks, focusing on thin-skinned, less-visible areas such as ears, eyelids, muzzle, chest, belly, mane and tail. Full body tick checks are recommended after equines have been in areas where ticks may be more common, such as after trail rides in brushy habitat.  

• Apply EPA-registered pyrethroid-based sprays labeled for equine use. Reapplication may be needed based on rainfall or sweat exposure and is typically only effective for short-term applications.  

• Fly sheets or insect barriers may provide partial protection from both biting flies and ticks.  

• Avoid off-label or overuse of pesticide products to prevent skin irritation or systemic absorption. Consultation with a veterinarian before application of on-animal chemical products is highly recommended.  

When to Heighten Vigilance  

• After trail rides or turnout in brushy or wooded areas.  

• During peak tick activity months: spring through fall, although milder winters may support year-round activity in parts of the Southeast and South-Central U.S.  

Veterinary Role in Surveillance and Education  

Veterinarians are well-positioned to contribute to equine welfare through owner and caretaker education on tick-borne diseases and bites and preventative approaches for tick and other arthropod-borne diseases and associated conditions. In many states, ticks can be submitted for identification through the state’s Departments of Agriculture, Environmental Health or Public Health Departments, or through state Extension services. In Kentucky, suspected Asian longhorned ticks can be submitted through the University of Kentucky Cooperative Extension Service by bringing them to your county Extension office, mailing them to the Entomology Department through the contact information below or by contacting the Office of the State Veterinarian at statevet@ky.gov.  

For identification of suspected Asian longhorned tick in Kentucky, please preserve specimens in ethanol or hand sanitizer (without additives like aloe), or in a ziplocked bag after freezing specimens (to kill ticks). Mail specimens to University of Kentucky Veterinary Entomologist, Dr. Hannah Tiffin, at the University of Kentucky S-225 Ag Science North Lexington, KY 40546-0091 along with information on date of collection, host animal collected from, county of collection, and follow-up contact information. 

Editor’s note: This is an excerpt from Equine Disease Quarterly, Vol. 34, Issue 1, funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents. It was written by Hannah Tiffin, PhD, assistant professor at the University of Kentucky, in Lexington.   

Consider these 8 behaviors that could suggest your horse is struggling to see.

You’re walking peacefully along a quiet trail in the woods with your trusty equine friend when, suddenly, you find yourself clinging to the side of the saddle, with your heart beating out of your chest.

Your horse, meanwhile, stands under you, stiff-backed with ears perked, snorting at a stump.

A stump. A measly, graying, run-of-the-mill stump, the likes of which you and your horse have certainly crossed paths at least a dozen times.

You tell yourself, “That’s it—he’s gone completely berserk.” But over time, you start connecting the dots. You realize this spookiness has taken on a pattern.

Indeed, your steed only seems to spook at objects on his left side, for example, and generally on days and during hours when trees cast dark shadows, contrasting the otherwise general brightness of daylight. And that’s when you start to wonder: Is my horse still seeing okay?

It’s a question horse owners regularly pose to equine vision specialist Nicole Scherrer, BA, DVM, Dipl. ACVO, associate professor of clinical large animal ophthalmology at the University of Pennsylvania School of Veterinary Medicine’s New Bolton Center, in Kennett Square.

It’s also a mysterious issue equine ophthalmologist Richard McMullen, Dr. med. vet., Dipl. ACVO/ECVO has been studying in-depth in his role as a senior veterinarian in the equine ophthalmology service at the University of Zurich’s Vetsuisse Faculty, in Switzerland.

“If I had a wish, it would be to look through a horse’s eyes for a day because it’s really difficult to know how much they rely on vision,” he says.

Finding the Behavioral Signs of Vision Loss: a Blind Path?

Certainly, vision problems can affect horses’ behavior, Scherrer says. But the types of behaviors can vary vastly from one individual to another. “I don’t even think I can give an exhaustive list of them,” she explains.

Plus, those behaviors can have multiple causes beyond vision issues, McMullen cautions. “I used to think it was so cut-and-dried: They’re shying, they’re bumping into things, they don’t like going from light to dark,” he says. “But there are all kinds of reasons horses do these things. The more cases I see, the more difficult it is to determine what the signs really mean.” 

So, while our sources say it’s impossible to create a definitive checklist of vision-related behaviors, they’ve shared some hints that might suggest your horse is having vision issues. However, they emphasize this list should in no way serve as a diagnostic resource.

In general, vision problems affect one eye more than the other, adds Scherrer. So, if any of these behaviors occur more on one side than the other, that’s a more convincing sign vision troubles could be at play.

1. Spooking or Refusing.

Arguably, the most common reasons owners seek vision workups for their horses are spooking and refusing obstacles, our sources say.

It’s a reasonable assumption—provided the behavior is a new development, says Scherrer. Growing cataracts, for example, can trigger spooking in previously nonspooking horses, she says. That’s especially true if the horse shies when something or someone approaches from his side, because cataracts can block vision at certain angles. Even so, cataracts in other parts of the eye could also affect forward-facing vision, which might interfere with understanding obstacles, for example.

“It could be anything, like stopping at jumps, or maybe having trouble finding distances, whereas they used to be seeing distances just fine,” she says, adding that some horses with flawed vision even balk at specific colors.

That said, many vision-impaired but experienced show jumpers perform very well, notes McMullen. This success is largely due to their ability to draw on previous training and rely on their riders “to accomplish what they need to accomplish,” he says.

Likewise, it’s important to remember that horses can spook for many reasons, he adds. “We get lots of horses referred for spooking, but when we perform a complete ophthalmic examination, we often find no visual defects or refractive errors—meaning they should be able to process incoming light normally,” he says.

2. Reacting Differently to Bright vs. Dark Conditions.

Horses that react differently to various lighting situations could have vision issues, possibly caused by corpora nigra cysts—“little brown balls” in the iris that can grow into larger cysts, which interfere with normal vision, says Scherrer. In bright light, when the pupils are smaller, the cysts take up more of horses’ field of view. “These horses tend to be worse on a really sunny day or out on the cross-country course versus working indoors,” she says. 

In addition, vision-impaired horses might not want to move from bright to darker areas, or vice versa, says McMullen. They could also be wary about stepping between brighter and darker surfaces.

3. Turning the Head in Unusual or Unexpected Positions.

When a horse has particularly uneven vision between his eyes, he might tilt his head or bend his neck to see better view with the stronger eye. This behavior typically occurs only when there is severe or complete vision loss in one eye, Scherrer says.

Certain pathologies (disease or damage) can also affect specific areas of the eye, affecting the way horses adjust their head and neck positions, she adds. “I had a client horse with a cloudy corneal disease called immune-mediated keratitis, and it was on the bottom half of the cornea,” she recalls. “The horse couldn’t find the carrot during low carrot stretches. But once we treated her and her cornea cleared up, she was able to find the carrot again.”

4. Bumping Into Things.

Horses that don’t see well sometimes bump into fences, poles, people, horses, or objects—and then seem surprised about it, McMullen says.

Bumping behavior appears early in young horses with congenital vision issues such as severe retinal problems or cataracts, he says. It can also occur in older horses with sudden onset of vision problems.

Those with more progressive disease processes—meaning they gradually worsen—are less likely to bump into objects due to their training and performance experience, McMullen explains.

5. Getting ‘Lost’ in a New Pasture or When Separated From a Friend.

Some vision-challenged horses might struggle to maintain rank in the social hierarchy if they can’t see well enough to defend resources such as food and shelter, our sources say. But in general, they adapt smoothly in the pasture.

“The last thing a horse wants to do is draw attention to itself and change its status within the herd,” McMullen says. “So if they become visually compromised, that could be a huge problem for them—and it might be part of the reason they’re so good at adapting and covering up those changes.”

“Their whole drive is to not let anyone see that they have a problem,” Scherrer adds. “They do a really good job of pretending that everything’s okay.”

That all changes, though, if these horses lose familiar elements in their environment. “Maybe they’re moved to a different field, or a friend dies, and then all of a sudden they look like they’ve gone acutely blind,” she says.

That’s also the case with vision-impaired horses moving to a new facility or competing in an unknown venue, McMullen adds.

“When I see these horses come in for evaluation, I usually find chronic changes,” Scherrer continues. “So it’s not something recent—it’s just that they’d been really good at hiding their disabilities up to then.”

But even in new environments, visually impaired horses adapt remarkably well, she adds. Her own pony—whose eye troubles eventually led to surgical removal of both eyes—was galloping in a new field within weeks of surgery. “By the second week, you would never have known that that pony was blind, given how she negotiated around the property,” Scherrer says, adding that the mare appeared to “memorize the location” and depend on her herdmates.

6. Headshaking, Increased Blinking, or Squinting.

Headshaking can have multiple causes, but Scherrer says vision problems are certainly worth considering. Specifically, horses with floating structures in the field of view can find their movement “irritating,” prompting them to shake their heads. That can also be the case with corpa nigra cysts, which can be somewhat mobile, she says.

If the vision issues involve pain, horses might blink more often than usual or seem to “squint”—meaning any downward deviation of the upper eyelashes. “Standing in front of the horse can allow you to easily compare the eyelash angle on one eye to the other,” she says. 

Unlike humans, however, horses rarely have issues with eye focus that lead to squinting or blinking, she adds.

7. Grumpiness, Stubbornness, or Any Recent Behavior Change.

Importantly, behavior problems could reflect vision issues truly upsetting and confusing for the horse, our sources say.

Indeed, horses’ reactions to vision loss can be so broad and varied it’s often impossible to associate specific behaviors with specific vision problems, McMullen says. “We often find really significant lesions during an exam, but they are often not associated with behavioral patterns matching that kind of vision loss,” he explains.

Even so, any abrupt new behavior can be an important clue. “Acute behavior changes are always a good indication to look to see if there’s something going on in the eyes,” he says.

“The biggest thing, especially if they’ve had the horse for a while, is any type of change,” Scherrer seconds. “Most of the time when we find an actual eye problem as the cause of a behavior issue, it’s something that the horse had started doing over the last six months to a year or so.”

Some horses—especially stoic breeds such as stock horses—might simply act a little grumpier or more stubborn than they used to, she explains.

“Every time I see something in the horse’s eye, my job is to ask myself, ‘Okay, do these clinical signs meet what I’m seeing in the eye?’” she says. “If there’s any question of a behavior change, it’s just a good idea to get an eye exam.”

Owners can request basic exams from their treating veterinarians during regular checkups or get a specialist referral for more advanced testing. “It’s always worthwhile to mention these things to your vet,” she says.

McMullen agrees. “It’s fairly easy to thoroughly look at the eyes,” he says. “And then if there are no findings, you can start looking for other issues that might explain the problem.”

8. No Unusual Behavior at All.

Because horses have evolved to hide their weaknesses from predators and herdmates, many show no signs of vision loss at all, says Scherrer.

“There’s not necessarily a red flag that goes up for these animals,” McMullen says. “They just tend to adjust really well and accommodate for vision loss—often to the point where they’re completely blind in one or both eyes, and nobody knows it.”

“I’ve even seen horses come in to the clinic who are close to blindness, with disease that’s clearly been going on for years, and their—very good—owners have never even seen them squint,” adds Scherrer, who in a recent study of more than 500 horses found that well-meaning owners frequently noticed no signs whatsoever of minor cataracts.

“It can be really hard to interpret when you have a tricky horse like that,” she says.

Take-Home Message

Horses can cope remarkably well with vision issues—even extreme cases involving blindness—making it difficult for owners to pick up on behavioral signs that their horses are struggling to see well. Still, careful observation can sometimes pick on possible signs meriting a vision workup, at least to rule out sight as a cause. For optimal equine health and welfare, our sources recommend having your veterinarian investigate any new behavioral problems in horses for vision and other health issues, our sources say.

This article is from the Older Horse 2025 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.

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Know when your horse might need one of these important vaccines

Vaccination serves as a core component of equine preventive medicine that can help keep your horse and others safe from dangerous and potentially deadly diseases. Ideally, equine veterinarians administer vaccines early in the year to prepare horses’ immune systems for the coming months when they will likely have the most exposure to some potentially infectious pathogens.

Core vaccines are a necessary part of all horses’ yearly wellness plans with their veterinarians. Regardless of your horse’s activity level, housing, or use, the American Veterinary Medical Association (AVMA) and American Association of Equine Practitioners (AAEP) recommend vaccinating horses annually against diseases that have the potential to affect public (horse and human) health, must be vaccinated against by law, or can cause severe disease or death. These include rabies, tetanus, West Nile virus, and Eastern and Western equine encephalomyelitis (EEE and WEE).

“Core (equine) vaccines are those vaccines that are recommended for all horses, at least annually,” says Elizabeth Davis, DVM, PhD, Dipl. ACVIM, professor and associate dean of clinical programs at Kansas State University’s College of Veterinary Medicine, in Manhattan. “These are diseases that we should recognize that a horse could contract while standing in a pasture, and they are typically diseases that if infected, will be likely to result in serious if not life-threatening and possibly zoonotic (contagious to humans, in the case of rabies) disease.”

Veterinarians administer risk-based vaccines, however, based on a horse’s potential to contract certain diseases, after the owner and veterinarian perform a risk-benefit analysis. Risk-based vaccine plans can vary regionally and should be tailored to the individual horse or farm. When managing a group of horses, combining meticulous biosecurity practices with a strict vaccination protocol can help reduce disease risk.

Risk-Based Vaccines for Horses

Most often, horse owners and their veterinarians determine what risk-based vaccines, if any, a horse could benefit from based on his location, workload, frequency of travel, and resident herd status (i.e., how much the horses leave the farm and commingle with others). The AAEP lists the available risk-based vaccines as:

• Anthrax Horses can contract this serious, septicemic (caused by the spread of bacteria and their toxins in the bloodstream) disease through inhalation, contamination of a wound, ingestion, or mechanical transmission by blood-sucking insects. Horses in geographic locations with alkaline soil are at the highest risk because this environment supports Bacillus anthracis (the causative bacterium) spore survival. Anthrax carries a high mortality rate and can be transmitted between animals of different species.
  
• Equine influenza is the most common respiratory disease in horses and is highly contagious. The virus can spread rapidly through aerosolized droplets distributed when infected horses cough and clear their airways. The most common clinical signs include coughing and abnormal respiratory sounds but also fever, edema, and enlarged lymph nodes.
  
• Botulism This is the most potent known biological toxin, produced by the bacterium Clostridium botulinum. It causes neurologic clinical signs beginning with weakness and quickly progressing to paralysis and often death. The bacterium can be found in decaying animal carcasses or plant material, and horses contract it by inadvertently ingesting it while grazing or eating hay. 
  
• Leptospirosis Infected animals, including wildlife, spread the causative bacteria, Leptospira, through urine and other bodily fluids. Horses can be exposed via open wounds or the mucous membranes, most commonly via water or soil. Clinical signs can include uveitis (ocular inflammation), placentitis or abortion in pregnant mares, or acute renal failure.
  
• Potomac horse fever While this infection most commonly occurs in horses in the eastern United States residing near the Potomac River, cases have been reported worldwide. Horses are most likely to be infected with the causative bacterium, Neorickettsia risticii, between late spring and early fall. N. risticii has a complex life cycle, first infecting parasites of freshwater snails, which the snails release when the water is warm, then infecting larval stages of aquatic insects such as caddisflies, mayflies, damselflies, dragonflies, and stoneflies. These aquatic flies thrive abundantly during specific times of the year and can serve as a reservoir for potential infection during the summer and fall months; typically, horses ingest the flies after they’re attracted to lights in the barn and fall into horses’ feed buckets and hay, or they can ingest them in water. Clinical signs vary but can include diarrhea, fever, mild/moderate colic, and acute laminitis.
  
• Snakebite In areas where venomous snakes such as rattlesnakes and copperheads are abundant, horses have a higher risk of getting bitten, which can lead to death if not treated immediately. Clinical signs can vary based on the type of snake but typically include pain and swelling at the site of the bite. After horses have recovered from snakebite, veterinarians typically monitor them for heart failure or kidney damage, which can occur in the weeks following the bite.
  
• Strangles, caused by the bacterium Streptococcus equi subspecies equi, most commonly infects young horses. Some infected horses might become carriers for an extended time, meaning they can shed S. equi for months or years. This disease is highly transmissible through both direct (i.e., nose to nose contact between horses) and indirect (i.e., a horse drinking from a water bucket that an infected horse used) contact between horses. Infected horses typically exhibit clinical signs such as fever and nasal discharge or pus draining from ruptured lymph nodes around the throat.
  
• Rotavirus This viral infection is spread through the fecal-oral route and is a common cause of illness and death in foals, though it can be largely prevented by vaccinating the dam during pregnancy. Infected foals typically have diarrhea, are lethargic, and will not eat. Although a vaccine for foals exists, there is no published research showing evidence that the vaccine can provide them significant protection.
  
• Equine viral arteritis While typically not life-threatening to adult horses, equine arteritis virus is spread through respiratory secretions in close quarters (i.e., horses stabled near one another), fomites (brushes, humans, etc.), and breeding. Equine viral arteritis can cause abortion in mares, death in young foals, and stallions typically become lifelong carriers. Clinical signs of equine viral arteritis can vary greatly from fever and depression to localized swelling of the limbs (especially hind limbs), scrotum or mammary glands, and underside of the abdomen.
  
• Equine herpesvirus-1 and -4 are most common in horses that commingle with horses from other farms. Both are spread by direct and indirect contact and in many cases establish latent (hidden) infection in horses that then become asymptomatic carriers. Clinical signs of EHV-1 include respiratory disease, abortion, and neurologic defects, while EHV-4 typically causes respiratory disease.
  
• Venezuelan equine encephalomyelitis Horses living in Southern Texas, California, Louisiana, Mississippi, Alabama, and the west coast of Florida have the highest risk of contracting this disease, which is most often seen in Central and South America. This virus is also typically transmitted through mosquitoes. Venezuelan equine encephalomyelitis can cause fever, depression, paralysis, gait abnormalities, and seizures, but the prognosis depends upon the subtype of the virus.

Assessing Your Horse’s Risk

“It is important to make a risk-based decision to understand what is best for the individual horse and the population in which it lives,” says Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM, professor of equine internal medicine, Patsy Link professor of equine research, and associate department head for research and graduate studies in the Department of Clinical Sciences at Texas A&M University’s School of Veterinary Medicine and Biomedical Sciences, in College Station. Not all risk-based vaccines are necessary for every horse, and some might be harmful to certain groups of horses, he adds.

Practitioners might recommend vaccinating horses based on the resident farm population’s risk. An older horse that stays on the farm could have a decreased risk of developing some diseases, but his veterinarian might recommend vaccinating him because young show horses also live on the property.

“Vaccinating the older horse might strengthen herd immunity even if it has little impact for the individual horse,” says Cohen. “Risk-based vaccination should be considered case-by-case (where the case might be a horse, a herd, or both) and there is subjectivity in this decision-making process. For example, a veterinarian might recommend that horses be vaccinated for strangles at a farm with a history of this disease, but not for other horses living in settings where the disease is considered low risk. Another veterinarian might say vaccinating all horses for strangles would reduce the burden of disease for all horses.”

Practitioners often decide which risk-based vaccines a horse should receive based on geographic location, likelihood of exposure, and the horse’s use, adds Davis. “Working directly with a licensed veterinarian is the best way to establish a protocol that is appropriate for a specific horse or situation,” she says. The AAEP consistently collaborates with researchers to develop and publish current recommendations for equine veterinarians and owners to access.

Horses that travel frequently, are exposed to horses from other farms, and are in stressful situations such as horse shows are more likely to develop respiratory disease, notes Davis. “Intense exercise and long-distance travel have been shown to reduce immune function when combined with exposure to other horses that may be shedding pathogens,” she says.

For example, show horses that stable near horses from other farms at competitions or travel with strange horses to and from shows might be more likely to contract EHV-1 and/or -4 than horses that do not have contact with others; therefore, it is important to maintain vaccine protocols as outlined by sport governing bodies such as US Equestrian. “In most instances, show regulations require proof of vaccination against EIV/EHV-1/4 at least every six months,” says Davis. “These vaccines must be maintained on a regular basis and must be administered by a licensed veterinarian.”

Common Risk-Based Vaccine Misconceptions

“A myth that is sometimes shared is that horses maintained on a farm setting or used for breeding are not at risk for disease other than those included with core vaccines,” says Davis. “It is important to recognize that horses leaving and returning to a property can potentially pose risk to other residents.” Horses that live close to others, especially those that share a fence line with horses from another farm, are also at an increased risk of contracting disease even if it might not appear that way, she adds.

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“The risks posed by vaccines have been the subject of much misinformation in both human and veterinary medicine,” says Cohen. “There is little doubt that the benefits of vaccines vastly outweigh the risks. As an equine veterinarian, I hate to think where we would be without vaccines for tetanus, West Nile virus, or rabies.”

Vaccines should always be given to otherwise healthy horses to minimize the risk of adverse reactions.

“In the rare circumstances when an adverse reaction occurs from a vaccine in a healthy horse, it is perceived as more harmful than when an adverse reaction occurs from using a medication used to treat an illness,” Cohen adds. “Preventing disease is a much more effective way of controlling disease than treating cases, but curing an animal of disease is often more compelling to horse owners than preventing disease in a healthy horse.”

Even if a horse develops a disease shortly after vaccination, it’s important to understand it might be coincidental; while adverse reactions do occur, they are much rarer than coincidental events, says Cohen. They are also often—but not always—relatively minor. “The diseases prevented are more serious than the most commonly reported adverse reactions such as swelling or soreness at the vaccine site,” he says. “The USDA’s Center for Veterinary Biologics that licenses vaccines for veterinary medicine has always set a high bar for safety of vaccines, and my limited experience has been that companies that manufacture vaccines consider (product) safety to be just as important as efficacy.”

Take-Home Message

Work closely with your veterinarian to develop a risk-based vaccine plan. Evaluate needs of the individual horse, the herd in which he lives, geographic location, age, and use before determining necessary vaccines. Preventing disease is one of the best ways to improve equine health and welfare. “I think people forget how valuable vaccines are for equine health,” says Cohen. “Failure to vaccinate horses appropriately increases risks for the individual horse, the horses in its population, and—for some diseases like rabies—human health as well.”

Respiratory health directly affects how well a horse can perform, and viral infections in the lungs or airways can seriously interfere with a sport horse’s abilities. Scientists have long known that acute respiratory infections reduce equine performance, but the impact of subclinical (inapparent) viral infections remains less clear, said Thibault Frippiat, DVM, Dipl. ECVSMR, of the University of Liege’s Faculty of Veterinary Medicine, in Belgium. In a recent literature review he and his coauthors, including Dominique-Marie Votion, DVM, Dipl. ECVSMR, evaluated the prevalence of respiratory viruses, how they affected horses clinically, and management strategies.

The Most Common Respiratory Viruses Found in Sport Horses

The research team pointed out the high prevalence of respiratory viruses in both clinically healthy horses and horses exhibiting clinical signs of respiratory illness. When analyzing data from studies that collectively included over 45,000 horses, they found that:

• Equid gammaherpesviruses (EHV-2 and EHV-5) were extremely prevalent, detected in about one-third of all horses, regardless of health status.
• Equid alphaherpesvirus-4 (EHV-4) and equine influenza virus (EIV) were significantly more common in horses with acute respiratory disease than clinically healthy animals.
• Equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), and equine rhinitis A virus (ERAV) were rarely detected in either healthy horses or those showing clinical signs of illness.
• Equine rhinitis B virus (ERBV) was frequently found in horses displaying respiratory illness and might contribute to coinfections with other pathogens.

So while certain viruses lead to clinical disease, others might cause only subclinical infections. These silent infections could contribute to airway inflammation and reduced respiratory efficiency in sport horses, the researchers said, potentially impairing performance without manifesting as signs of illness.

What Does This Mean for Veterinarians and Horse Owners?

For practitioners and horse owners, these results highlight the importance of biosecurity efforts at equine events. Events pose a heightened risk for viral transmission because large groups of horses from different farms congregate in one location, said Frippiat. For certain diseases vaccination remains a cornerstone of prevention, helping mitigate clinical severity and viral spread.

Horse owners should remember that even without visible signs of illness, certain viruses can still hinder a horse’s ability to train or compete. And when horses do show clinical signs, such as fever, coughing, nasal discharge, or other signs of illness such as poor performance, owners need to consult their veterinarians, Frippiat added. Subtle signs of poor performance due to respiratory disease might include tiring easily or having poor results in the show ring (i.e., a show jumper knocking down more rails than normal).

Future Respiratory Research in Horses

While the researchers consolidated existing knowledge, they also highlighted gaps that call for further investigation, said Frippiat. He noted that researchers should further examine how subclinical viral infections affect performance limitations in sport horses.

Advancements in rapid on-site diagnostic tools, such as PCR-based systems, will enhance early viral detection and containment efforts. These systems continue to emerge, he said, but veterinarians need to validate them scientifically before putting them into practice.

Take-Home Message

Respiratory viruses pose ongoing challenges for equine athletes, with potential effects ranging from acute illness to subtle declines in performance. Through strategic vaccination, enhanced biosecurity, and improved diagnostics, veterinarians and horse owners can work together to mitigate these threats and safeguard the health, welfare, and performance of sport horses.

The study, “Respiratory viruses affecting health and performance in equine athletes,” appeared in Virology in December 2024.

Q. My horse gets frequent bouts of cellulitis. I work closely with my vet to treat and prevent this medically, but is there anything I can do to support our efforts through his diet?

A. Cellulitis is a bacterial infection that involves both the connective tissue and the fat tissue, most frequently presenting in the lower limb of the horse, and can be a challenging health issue. There are multiple causes of the condition; however, the infection normally enters the body through small (often undetectable) microtraumas on the skin surface.

Medical management is critical to resolving these cases, so it is great that you are working closely with your veterinarian. For treatment, the goal is to reduce the inflammation, eliminate the infection, and reduce the likelihood of the infection recurring.

A Balanced Diet for Horses With Cellulitis

Although nutritional management is not a cure for cellulitis, there are some dietary changes you can make to support your medical efforts. A balanced diet is imperative to maintaining both skin health and the immune system. Providing your horse with a feed or ration balancer (fed at the manufacturer’s recommended amount) is an important factor. Inadequate protein (amino acids), vitamin deficiencies, and unbalanced minerals can all negatively impact the health of a horse’s skin and hair coat, so pursuing a balanced diet for your horse with appropriate levels of vitamins, minerals, protein, and energy is important to promote optimal health.

Vitamin E & Omega-3s to Reduce Inflammation in Horses

When inflammatory issues are present, adding vitamin E and a source of omega-3 fatty acids is also a common recommendation. For your horse, if he is on a balanced diet, I recommend having his vitamin E levels tested via blood serum. If the levels are adequate, then there is no need for additional supplementation but, if he has a deficiency, supplementing with a natural source of vitamin E can help support your efforts to prevent cellulitis. 

When adding omega-3s, opt for a fat source that is greater in omega-3 content than omega-6 content (while one omega-6 type has been studied for its beneficial effects, omega-6s are generally considered to have pro- rather than anti-inflammatory properties; the ratio of the two seems to be what’s important). Oils such as flax or camelina are good options and can be fed at a rate of 1-2 oz per day to start and increased to 2-4 oz per day if your horse needs additional fat. Adding fat to the diet can help your horse maintain the protective barrier of sebum on his coat. This is especially important if your horse has dry skin and is prone to cellulitis. If your horse is not overweight, adding an omega-3-rich fat source to his daily ration can be a good way to support the prevention of cellulitis.

Digestive Support for Cellulitis

Because the cellulitis episodes are frequent, you could try a digestive support supplement for your horse. Regular administration of non-steroidal anti-inflammatory drugs (NSAIDs) and/or antibiotics can disrupt his gastrointestinal tract. Of course, a balanced forage-based diet will be a key factor in maintaining your horse’s gut health, but adding a pH control supplement for the gut could provide extra support. When choosing a supplement, evaluate the research on the product to ensure what you are investing in will support for your horse.

Take-Home Message

When cellulitis bouts occur, seeking medical management and guidance on optimal treatment from your veterinarian should be the first step. However, there are some nutritional considerations that can support your horse in addition to the medical efforts. A balanced diet that provides your horse adequate nutrients is imperative to his overall health. Adding a fat source that is rich in omega-3s and investigating digestive support supplements to use when your horse is on NSAIDs or antibiotics could reduce the negative effects these medications might have on his digestive system.

Do you have an equine nutrition question?

Q: With summer approaching, I want to be sure I’m prepared to minimize unpleasant odors on my farm that are always worse during the warmer months. What can I do to eliminate those odors or prevent them altogether?

A: During the warm season horse properties can develop odors—between muddy turnouts, stockpiled manure, and urine buildup in confinement areas. These spots attract pests such as flies and rodents and can raise concerns among neighbors. Inhaling ammonia in stalls, barns, or confined spaces can also harm a horse’s respiratory tract. Here are five tips to help you reduce odors on your horse property.

1. Start With Healthy Soil

Odor control starts with a step many people overlook: Start with healthy soils and slightly sloped ground. If you confine horses in a low, wet area you will end up with mud and odor problems. Make sure you have a good, even slope (about 1-2%) away from stalls or shelters. Be sure to grade the ground, making it even before putting gravel or another type of footing in these areas. Otherwise, any depressions in the underlying soil allow water (and urine) to pool under the gravel, potentially causing odors.

2. Develop a Manure Management Program

A solid manure management program goes a long way in solving odor issues. Begin by picking up manure every one to three days in confinement and high-traffic areas. Establish your manure pile far away from streams, ditches, rivers, or other bodies of water to prevent runoff contamination, and cover it with a tarp (to keep it from getting soaked by rain).

Let’s say you’ve picked up manure and you still have odors. The simplest and cheapest solution might be to drag or harrow the paddock. This helps get beneficial aerobic microbes back in your soil that break down tiny, odor-causing organics. It also helps the ground dry faster.

3. Minimize Moisture

Keep your farm as dry as possible by removing opportunities for standing water to form. Keeping shelters, stalls, and barns dry, or at least well-drained, goes a long way in reducing odors. Moisture often triggers odor problems; wet areas release more odor-causing compounds than dry ones. Consider doors, screens, or roof overhangs for shielding barn openings from rain. Invest in good working gutters and downspouts, which divert rainwater away from buildings and confinement areas. Ventilation also helps dry the barn area by releasing and not trapping moisture and allowing odors to dissipate. Stall windows, open doorways, cupolas and vents in roofs, ceiling fans, etc., can all improve ventilation in your barn.

If a horse perpetually urinates in one spot in a confinement area, you might have to occasionally dig out and refresh footing in that spot to help it dry thoroughly.

4. Use Microbial Sprays to Minimize Odors

A variety of microbial spray products are available, which you can use on urine spots and across confinement areas to neutralize odors. These products contain different types of beneficial bacteria, enzymes, and/or fungi. They come in highly concentrated solutions that you dilute and spray on paddock areas with a garden sprayer. The beneficial microbes break down ammonia and organic material that cause odors and attract flies. Use these animal-safe solutions as often as needed to control odors. You can commonly find these beneficial microbial sprays at organic garden supply companies or feed stores.

5. Use Zeolite Products in Stalls

Zeolite products remove odors effectively when you sprinkle them in stalls or other areas of your barn. These naturally occurring minerals have a highly porous structure, which binds with ammonia molecules in urine, eliminating odors. You’ll find zeolite, which looks like finely ground kitty litter, in several stall deodorizer products.

Take-Home Message

Starting with healthy soil, developing a manure management program, minimizing moisture, and using microbial sprays and zeolite products can all help reduce the odors on your horse farm. In turn, this will minimize pests and support your horses’ comfort and well-being.

Scratches, or equine pastern dermatitis (EPD), is not a disease but, rather, a cutaneous reaction pattern. Veterinarians and owners must address the primary, predisposing, and perpetuating causative factors for a successful outcome. Note that treating the predisposing and perpetuating factors is just as important as addressing the primary cause.

Clinical Signs and Pathogenesis of Scratches in Horses

Scratches can affect any breed, but is most prevalent in draft horses due to long pastern hair (“feathers”). It most commonly affects the rear aspect of the hind pasterns and especially nonpigmented skin. Without treatment the lesions can spread to the front of the pastern and fetlock. Clinical signs vary, but initially owners might notice edema (fluid swelling), redness, and scaling, rapidly progressing to oozing, hair matting, and crusting. If the cause is vasculitis (blood vessel wall inflammation), ulcers might form on the skin. Secondary bacterial infection is a common complication and can perpetuate the signs. In chronic cases skin can thicken and fissure due to constant movement and flexion in this area. The lesions are often painful.

Diagnosing Scratches in Horses

In a veterinarian’s detailed history, he or she should include the horse’s age, month of onset, whether the scratches is seasonal and/or pruritic (itchy), if there has been overzealous use of topical medications or home remedies, and response to prior treatment. He or she should also inspect the environment because wet or chemically treated bedding, along with muddy pastures and insects, can cause allergic contact dermatitis (from allergens touching the skin). If in-contact animals or humans are also affected it might indicate an infectious or zoonotic condition such as dermatophytosis (fungal infection). Another diagnostic rule-out is parasites—chorioptic mange is a common cause of pastern dermatitis in draft horses. But more commonly the cause of pastern folliculitis (a pus-forming skin infection) is bacterial, with Staphylococcus aureus and Dermatophilus congolensis as the culprits. Horses with white extremities can suffer from photosensitization  or immune-mediated pastern leukocytoclastic vasculitis (PLV), both exacerbated by UV light. Based on the information provided, your veterinarian might pursue specific diagnostics such as skin scrapings, fungal cultures, tape impression, skin cytology, skin biopsies, allergy testing, or bloodwork.

Treatments

After your veterinarian identifies the causative factors, it’s time to pursue appropriate therapy. Here are some environmental changes you can make:

1. Avoid turning affected horses out in pastures with mud, water, or sand, which can worsen the condition.
2. Keep horses in clean, dry stalls during wet weather.
3. Do not turn horses out until the morning dew has dried.
4. If you suspect contact allergic dermatitis, try an alternate source of bedding that isn’t treated or aromatic.
5. Clip heavy feathers over the pasterns to reduce moisture retention.
6. If you suspect PLV, avoid UV light exposure by stabling the horse between 10 a.m. and 4 p.m. and/or wrapping the affected legs.
7. Clean affected skin immediately after exercise using an antiseptic shampoo. 

Clinical treatments include topical and systemic therapeutics. Secondary infections with Staphylococcus spp are common and can complicate diagnosis. Available antibacterial shampoos typically contain ethyl lactate, accelerated hydrogen peroxide, 2% benzoyl peroxide, or 2% chlorhexidine. If lesions are exudative, apply astringent solutions, such as lime sulfur or aluminum acetate. 

Ointments such as silver sulfadiazine, fucidin, and 2% mupirocin ointment are available for treating localized bacterial infections. To treat bacteria, dermatophytes, or mites owners can apply lime sulfur dips and spray. Enilconazole spray or dip, along with miconazole shampoo with or without chlorhexidine shampoo, can be used to treat fungal infections. 

Sprays such as hydrocortisone aceponate or 0.015% triamcinolone can be used in conjunction with systemic immunomodulators to treat allergic and immune-mediated conditions such as PLV. In addition, veterinarians have noted success applying 0.1% topical mometasone, 1% betamethasone, or 0.05% aclometasone creams or ointments to lesions. Horses with immune-mediated conditions might also require immunosuppressive doses of dexamethasone or prednisolone. 

Antiparasitic approaches for Chorioptes include ivermectin, topical eprinomectin solution, selenium sulfide shampoo followed by lime sulfur, and fipronil spray.

Q: I have a 20-year-old Arabian/Paint gelding that I’ve had since he was 3 months old. He was always an easy keeper and I realized when he was around age 4 or 5 that he had equine metabolic syndrome (EMS).

From that day on, he’s consumed low-nonstructural-carbohydrate (NSC) hay and grain. Because he is an air fern, I’m always careful about what he eats and severely limit his grazing time; I keep him on a dry lot most of the time. At age 14 he developed pituitary pars intermedia dysfunction (PPID, formerly called equine Cushing’s disease). My veterinarian put him on 1.5 Prascend (pergolide) pills per day, which I administer in addition to Thyro-L (levothyroxine sodium).

Somewhere during all of this, my gelding started losing weight. He had a mild gastric ulcer attack a few years ago, so my veterinarian prescribed ranitidine, which she later replaced with cimetidine. Recently, he had another ulcer attack and currently has omeprazole added to his diet. My question is, how do you feed PPID, EMS, and ulcer-prone horses that need to gain weight? I already feed every four to five hours. Consuming oils never helped him, but soaked beet pulp has helped some.

A: Hello, I am sorry you’re having to handle these difficult issues. The first thing I recommend is having a good discussion with your veterinarian about your horse’s conditions to determine whether the current medications should stay the same or be adjusted. Veterinarians often prescribe Thyro-L to help horses regulate glucose and insulin and treat EMS. They also commonly prescribe Prascend, which you also mentioned, for horses with PPID. Both medications can cause weight loss—a side effect that usually benefits horses with EMS and PPID. However, your veterinarian might want to monitor the dosage and make adjustments if needed.

I am glad to hear your horse receives omeprazole for his ulcers. Currently it is the only FDA-approved medication for treatment and prevention of gastric ulcers in horses. I recommend talking with your veterinarian about whether you can discontinue this medication or reduce the dosage once management strategies help get the condition under control.

I would like to address feeding management of the three distinct disorders you mention—EMS, PPID, and gastric ulcers. Fortunately, some of the recommendations for managing these conditions overlap, which can make caring for your horse easier.

EMS

Horses with EMS tend to be easy keepers and carry extra weight, but you need to make sure you aren’t “starving” them to get them to an ideal weight. Forages low in NSCs should be the base of their diet. Typically, they should have only hay with little to no access to pasture, especially in fall and spring when pasture NSC levels tend to be higher. On a per-pound basis you’ll want to avoid feeding less than 1.5% of a horse’s body weight in hay. A low-calorie/low-sugar ration balancer can help you make sure you meet all his nutritional requirements. To help keep glucose and insulin levels steady, provide small, frequent meals and/or use a grazing muzzle to slow down feed intake.

PPID

Pituitary pars intermedia dysfunction cannot be managed with diet alone (hence, giving pergolide), but it can help. Overweight horses should receive a lower-calorie diet to promote weight loss, and horses with insulin resistance or insulin dysregulation (often referred to together as EMS), need a diet low in NSCs. If a horse with PPID has not been diagnosed with EMS, you can generally feed a balanced diet of forage and concentrates or a ration balancer, while monitoring weight to prevent excessive gain.

Gastric Ulcers

For horses prone to gastric ulcers, feeding recommendations try to decrease acidity (low pH) in the stomach. Horses are designed to be continuous feeders; some type of feed is in the stomach almost constantly. We can mimic this by providing horses with multiple small meals throughout the day and allowing free-choice access to forages. Nutritionists also recommend reducing the amount of concentrate a horse receives to address gastric pH. Higher-fat feeds tend to slow gastric emptying rate and are not as acidic as more traditional concentrates. Experts also suggest offering some feeds on the market that contain more complex carbohydrates. Adding a forage higher in calcium might also be beneficial, because it works as a natural antacid.

With both PPID and EMS the goal is to keep insulin levels regulated and maintain a horse’s body weight at a level that won’t predispose him to bouts of laminitis. I recommend you feed a good-quality mostly grass hay with an NSC level of less than 10%. If you can’t find hay with NSC levels below 10%, soak the lowest-NSC hay you can find for about 30 minutes prior to feeding to help reduce the sugar and starch content. Remember that you should not give your horses access to the soaking water because it will have all those undesirable carbohydrates in it. You should feed your horse about 2% of his body weight in forage daily—so about 20 pounds of hay for the average 1,000-pound horse.

I would also recommend a ration balancer if your horse maintains his weight on forage alone. Essentially, manufacturers design balancers to work as a vitamin and mineral supplement to ensure your horse gets the correct levels he needs. Make sure it is low in soluble carbohydrates. If he cannot maintain his weight on forage alone, then I recommend one of the higher-fiber feeds available. You mentioned your horse has consumed beet pulp, and it helped, whereas fats did not. Fortunately, many of these feeds have a beet-pulp base. These recommendations also work for the ulcer-prone horse, so they might help there as well.

It sounds like you are already taking many of the right steps for managing a horse with these three issues. Keep feeding meals more frequently and make sure you’re using low-NSC forages and feeds to maintain an appropriate body weight for your horse. I would be interested to hear what your veterinarian recommends related to the medications, and I wish you the best of luck.

Do you have an equine nutrition question?

Selective treatment strategies can combat antimicrobial resistance while protecting foals from R. equi

Rhodococcus equi is a hardy bacterium that lives in the soil and horse feces. It replicates in horse manure, so on densely stocked farms such as breeding operations, the environment can become heavily contaminated. When the bacterium becomes aerosolized—primarily due to environmental factors such as wind, dry conditions, and soil disturbances—foals can inhale it, potentially becoming infected.

Two forms of the bacterium exist: an avirulent form that is essentially benign for foals and another that is a virulent form. The virulent, disease-causing form has a specific genetic element called a plasmid with a gene that codes for a protein called the virulence-associated protein or VapA.

“The VapA protein enables R. equi to replicate inside immune cells in the lungs of foals, alveolar macrophages, leading to abscesses forming in the lung. This disease process is similar to what happens in tuberculosis, where the bacterium known as Mycobacterium tuberculosis is able to replicate in alveolar macrophages of humans to cause pneumonia,” explains Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM, of Texas A&M University’s College of Veterinary Medicine & Biomedical Sciences, in College Station. Cohen is professor of equine internal medicine, Glenn Blodgett Chair in Equine Studies, and associate department head for research and graduate studies in the college’s Department of Large Animal Clinical Sciences.

Foals living on endemic farms are exposed to virulent R. equi from birth and can become infected at a very young age. But most foals don’t exhibit clinical signs of pneumonia until they are 1 to 3 months old or older. Signs in foals resemble what we would see in a child: fever, lethargy, and coughing.

Experts say R. equi pneumonia poses significant challenges for the equine
industry due to a number of different factors, including:

1. The high costs of prevention/treatment;
2. The economic losses associated with foal mortality in severe cases; and
3. The reduced athletic potential of recovered foals as adults.

Further, antimicrobial resistance to medications often used to treat this condition adds to the complexity of managing R. equi.

In this article we’ll review some important facts about diagnosing and treating R. equi pneumonia, address issues related to antimicrobial resistance, and describe the work underway to create a not-so-secret weapon to fight this historically indomitable bacterium: a vaccine.

Fact No. 1: R. equi infection often leads to a self-resolving subclinical (without obvious clinical signs) pneumonia that typically does not need to be treated.

Veterinarians first started using thoracic ultrasonography in 2001 to screen foals for the presence of abscesses within the lungs suggestive of R. equi pneumonia.

“Studies conducted in 2005 and 2008 indicate that thoracic ultrasound screening and treatment of subclinical cases decreased the incidence of pneumonia and decreased the number of hospitalized foals,” says Angela Bordin, MS, PhD, assistant professor in the Department of Large Animal Clinical Sciences at Texas A&M.

This led to the widespread adoption of a screen-and-treat approach, where veterinarians began treating foals with evidence of pulmonary abscesses, even if the foals showed no clinical signs of pneumonia. 

In additional studies researchers discovered the following:

Fact No 2: Thoracic ultrasound exams at farms with endemic R. equi show that often more than 50% of foals are subclinically infected.

Fact No. 3: An estimated 70-85% of subclinically infected foals heal over time without treatment.

“This information led to the realization that not all foals with lung abscesses attributed to R. equi need to be treated,” explains Cohen.

But it was too late.

The Screen-and-Treat Fallout

“Thoracic ultrasound allows us to identify foals that have a lesion/abscess in their lungs before they have clinical disease,” says Bordin. “These lesions can progress to a severe pneumonia. Given there is no vaccine available, and the variability associated with Re-HIP administration (that of R.-equi-specific hyperimmune plasma), it is understandable that thoracic ultrasound seemed an attractive way to detect and treat foals with subclinical pneumonia.”

Avoiding R. equi infection is important because of the economic and welfare implications for farms and their horses.

“But the screen-and-treat strategy came with a price,” she continues. “Antimicrobial resistance in clinical isolates of R. equi from foals was rare before 2001, but it increased significantly after thoracic ultrasound screening. To exemplify, one study documented a higher prevalence of multidrug-resistant R. equi from 2007 to 2017 compared to 1999 to 2006 (Huber, 2018). In another study multidrug-resistant R. equi were isolated from soil samples of 76 out of 100 horse-breeding farms (Huber, 2019).”

Cohen concurs, adding, “As a result of the widespread, unnecessary use of antibiotics in foals without clinical signs of pneumonia, strains of R. equi resistant to the class of antibiotics most effective for treatment of rhodococcal pneumonia in foals began to emerge.”

A Closer Look at Antimicrobial Resistance to R. equi

“Antimicrobial resistance in R. equi is primarily driven by the acquisition of plasmids, which carry resistance genes for multiple antibiotics, including macrolides, aminoglycosides, and tetracyclines,” says Laura Huber, DVM, MSc, PhD, Dipl. ACVPM, assistant professor at the College of Veterinary Medicine, Auburn University, in Alabama. “These plasmids enable horizontal gene transfer between bacteria, allowing R. equi to rapidly acquire and spread resistance within microbial communities.”

Huber explains that the accumulation of antimicrobial residues from past antibiotic use can persist in the environment for many years, creating ongoing selective pressure that helps sustain antimicrobial resistance even after antibiotic use ends. In other words, the lingering antibiotics allow bacteria possessing resistant genes to survive and reproduce while killing off susceptible bacteria, leading to a population dominated by resistant strains over time.

“Our team is investigating the potential impact of antibiotic treatments in foals on the contamination of horse farm soil with antimicrobial residues,” says Huber. “We’re specifically studying how long these residues persist in the soil and how they contribute to the maintenance and spread of antimicrobial resistance, focusing on the long-term environmental effects of antibiotic use in animal care.”

And antimicrobial resistance can spread between different bacteria and species, creating a significant risk to other animals and humans.

“Rhodococcus equi is an ideal model for the One Health concept, as it links human, animal, and environmental health,” explains Huber. “The bacterium can be transmitted from the soil to both animals and humans, illustrating the interconnectedness of environmental, animal, and human health in the spread of infectious diseases and antimicrobial resistance.”

Treat for R. equi When Needed

Despite the bleak picture as far as R. equi antimicrobial resistance, Cohen stresses the importance of recognizing sick foals.

Fact No. 4: Foals diagnosed with R. equi pneumonia should be treated.

“The challenging part for veterinarians is that we do not yet know which foals will self-cure and which will require treatment,” says Cohen.

He and other experts say vets can make an R. equi pneumonia diagnosis based on:

• Farm history of R. equi pneumonia;
• Foals 1 to 6 six months old on the farm;
• The presence of appropriate clinical signs;
• Thoracic ultrasound or X rays showing lung abscesses or consolidation (areas filled with a substance besides air);
• Blood work showing a high white cell count and elevated concentration of inflammation-associated proteins such as fibrinogen or serum amyloid A; and
• Culture and microscopic examination (cytology) of a sterilely collected aspirate from the upper respiratory tract (trachea/bronchioles) to isolate and visualize bacteria and, ideally, identification of the VapA gene by polymerase chain reaction test (PCR).

Fact No. 5: Vets should not rely solely on thoracic ultrasonography to decide which foals to treat.

Further, veterinarians should not rely solely on blood work, such as a complete blood cell count, to diagnose R. equi; it’s better to also have cytologic or PCR evidence.

Fact No. 6: Foals infected with resistant strains of R. equi have a significantly lower survival rate compared to those infected with antimicrobial-susceptible strains.

When treating foals, experts have long recommended using a combination of rifampin and the macrolides azithromycin, clarithromycin, or tulathromycin. When resistance to rifampin exists, veterinarians can use the tetracycline antibiotic doxycycline as a substitute. But are these substitutions as effective as the rifampin/azithromycin combination once was?

“There needs to be more research on that,” Bordin says.

Preventive Strategies: The Elusive Vaccine and Re-HIP Therapy

Fact No. 7: Preventing disease is preferrable to overtreating. The goal of a prevention program is to reduce clinical pneumonia cases, thereby decreasing antimicrobial use and the subsequent development of antimicrobial resistance.

Vaccination

For many infectious diseases, vaccination has proven to be an effective preventive measure, decreasing the incidence and severity of diseases. But R. equi has proven a difficult pathogen for vaccine creation.

Various factors contribute to the challenge of developing a vaccine for R. equi. For example, this is an intracellular pathogen, and we lack a clear understanding of the immunity that protects against it.

“Foals are exposed to R. equi from birth and are most susceptible to infection when they are very young,” Cohen explains. “Their immune systems are naive and immature such that many foals can’t mount effective immune responses. But we know that giving foals the virulent organism in large numbers by stomach tube provides protection against infection, so we know that they can mount protective immune responses within the first few weeks of life.”

In his most recent attempt at creating a vaccine, Cohen, together with his research team, created a messenger RNA (mRNA) vaccine that encodes the VapA protein. After delivery—injection, in this case—the vaccine produces VapA in small amounts, which stimulates the foal’s immune system to mount immune responses to virulent R. equi strains. These immune responses are innate, meaning a general defense that happens immediately, and adaptive, which is a more specific response that occurs later.

“The vaccine did not work very well when delivered via nebulization directly to the lungs,” he notes. “When we gave it intramuscularly, that seemed to stimulate immune responses.”

Cohen says additional studies are needed to further determine if this mRNA vaccine is indeed worth pursuing in foals, or if efforts should return to producing an mRNA (or other) vaccine administered to pregnant mares instead.

“Vaccinating the mares may result in the production of antibodies against VapA that can be transferred to their foals through the colostrum and milk to protect the foal during the highly vulnerable period in the first weeks of life,” says Cohen. 

R. equi-Specific Hyperimmune Plasma (Re-HIP)

Most farms with endemic R. equi rely on Re-HIP for preventing infection in young foals. These plasma products are produced from mares vaccinated against R. equi using a product designed for adult horses. Foals receive Re-HIP intravenously shortly after birth, but the mechanism of action is unclear.

Although the approach was once considered controversial as far as its efficacy, Cohen says, “The bulk of the evidence indicates protective effects of transfusing hyperimmune plasma to foals, but the protective effects are not complete and vary among plasma products, farms, and individual foals. While we need better evidence in the form of well-controlled trials to get clearer evidence, current knowledge indicates that Re-HIP is the best prevention that we have available at this time.”

Fact No. 8: Experts recommend administering 2 liters of Re-HIP that has high activity against VapA to foals within the first day of life.

This conclusion is based largely on studies conducted by Cohen’s team, including a pinnacle study by Susanne Khan in 2019 published in Equine Veterinary Education.

“I think at most endemic farms, it makes sense both medically and financially to transfuse with anti-rhodococcal plasma because there is no effective alternative for controlling R. equi pneumonia,” says Cohen.

However, he notes that the advantages of Re-HIP are not as apparent on nonendemic horse farms.

“The decision as to whether to use Re-HIP needs to be made by the farm veterinarian, farm manager, and owners of the foals to assess both the risk of the disease and their levels of risk aversion,” Cohen says. “At nonendemic farms it is less clear whether costs and risks of Re-HIP outweigh the potential benefits of preventing something that may not be present.”

Future Directions in R. equi Research

Veterinarians gained valuable insights into R. equi through routine treatment following thoracic ultrasound screening in the early 2000s (based on the work of Steeve Giguère, DVM, PhD, Dipl. ACVIM, and others). However, our sources say much more research is necessary to get ahead of this economically draining disease. Specifically, vets need effective and efficient preventive strategies, ideally in the form of a vaccine, to prevent neonatal morbidity and mortality. 

“Because of limited availability of research funding, it will take years for researchers to test their ideas surrounding mare and foal vaccines,” says Cohen. “But we are nothing if not persistent and will continue to work hard to try to investigate an approach to protect foals.”

On the antibiotic-resistance front, Huber adds, “Responsible antibiotic use can slow the spread of antimicrobial resistance.”

She says veterinarians should use ultrasound to detect R. equi early and institute more targeted management, rather than relying on the screen-and-treat program. This approach would help reduce unnecessary antibiotic use. “Developing clear guidelines that combine ultrasound findings with clinical signs is crucial to avoid overuse of antimicrobials and ensuring that antibiotics are only administered when truly necessary,” says Huber. “While these approaches can help manage antimicrobial resistance, fully reversing the damage will require broader strategies, including improved (antimicrobial) stewardship and environmental control.”

This article is from the Spring 2025 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.

Q: This time of year, my horse’s mane and tail get very dry, and even his coat seems dry. I use coat conditioners when I bathe him, but I’m wondering what I could do nutritionally that might help?

A: If you live in a hot, dry climate, preventing a dry mane and tail and coat can be challenging. I find this to be especially true of horses living in dry lots or with dirt runs where they are basically rolling in dust.

Other than using topical products to try to maintain coat quality, the best you can do is to give the horse’s skin and coat a fighting chance by ensuring you’re feeding all the building blocks needed to maintain skin and coat health.

Minerals

Key nutritional players in this arena are zinc, copper, fatty acids, and biotin. Zinc is vitally important to a number of enzymes in skin. Epithelial cells that make up skin require zinc for reproduction, maintenance, and repair. Additionally the synthesis of keratins (proteins that protect epithelial cells and that are found in hair) and other associated proteins rely on zinc for proper function. While zinc is found in forages, the amounts present might not meet your horse’s needs.

Copper is generally in even shorter supply in forages than zinc. Copper is necessary for the enzyme lysyl oxidase, which in turn is required to maintain the structural integrity of the cross-linkages that provide strength to collagen in the skin.

Together copper and zinc impact melanin, the protein responsible for hair pigmentation. Therefore, inadequate copper and zinc status might not only impact the keratinization of hair but also its color. Hair is at greater risk of oxidative damage if melanin is inadequate.

If you’re just feeding forage, consider adding a source of copper and zinc that provides about half of the National Research Council’s daily requirement, which for a 1,100-pound horse is 50 milligrams of copper and 200 milligrams of zinc. My preferred method is using one of the quality ration balancing feeds and supplements available on the market because they also supply other essential nutrients that might be missing in a forage-based diet.

If you’re already feeding a commercial feed, make sure that you’re following the feeding directions and offering adequate amounts, otherwise your horse might have deficiencies in nutrients key to coat quality.

Fat

The cell membrane layers that connect the cells that make up hair contain large amounts of fatty acids. The fat in the cuticle cells make them hydrophobic, meaning they don’t attract water. This acts to make them waterproof but also keeps moisture in. Cuticle cells should lie flat like shingles on a roof, but if they become damaged, they peel away from the hair allowing internal moisture to escape.

Therefore, ensuring adequate amounts of essential fatty acids in the diet might help improve coat quality. I particularly like sources of supplemental fats that provide more omega-3 fatty acids than omega-6, such as flax or camelina. For coat improvement purposes, I find plant-based sources to be more than adequate, and about 4 ounces of flax seed or 2 ounces of the oils should be enough for you to see an improvement in an average-sized horse.

Biotin

While we typically think of biotin in relation to hoof health, biotin also plays a role in skin and coat. Biotin is a B vitamin that is actually made by the bacteria in the horse’s hindgut making biotin deficiency unlikely.

However, in other species inadequate biotin results in poor quality skin and coat. This makes sense when you consider that biotin involved in fatty acid synthesis, amino acid metabolism, and a range of other metabolic pathways. While there are no guidelines for how much biotin to supplement to see improvement in coat quality, research suggests 20 to 30 milligrams for and average-sized horse to aid in hoof quality and we can assume similar levels are necessary to see coat improvements.

Take-Home Message

Ensuring that your horse has the building blocks necessary to create a healthy coat from the inside is your best way to defend against a dry coat. However, make sure that you are not shampooing your horse too frequently as this can remove naturally occurring oils. Additionally, look for simple shampoos that contain few detergents and avoid those with alcohol as these can strip the oils from a horse’s coat.

Slow, progressive exercises help improve a horse’s strength and stability when recovering from this neurologic disease

Equine protozoal myeloencephalopathy (EPM) is a neurologic disease caused by the protozoa Sarcocystis neurona or Neospora hughesi and can lead to deficits including ataxia (incoordination), gait abnormalities, and muscle weakness or atrophy.

S. neurona is typically found in the Western Hemisphere, and the definitive host is the opossum. Opossums can get it by scavenging on infected cats, raccoons, and other intermediate hosts. Horses become infected by ingesting feed or water contaminated with opossum droppings. N. hughesi rarely causes EPM in horses, but sporadic cases arise from this organism. Researchers do not yet know what natural hosts can transmit N. hughesi.

Risk Factors for EPM

Researchers estimate 15-90% of horses have been exposed to S. neurona and, therefore, have antibodies in their bloodstream. However, exposure does not always lead to infection—the annual incidence of EPM is less than 1% in the United States. Horses diagnosed with EPM infection are often younger than 4 or older than 13 years old.

Veterinarians see the highest number of EPM cases during the fall, while the disease is much less common during the winter months. Stress, including immune system compromise, intense exercise, transportation, injury, surgery, or foaling can increase a horse’s chances of developing clinical (apparent) EPM.

Diagnosing EPM in Horses

When a horse exhibits clinical signs of EPM, veterinarians must distinguish the disease from lameness or other neurologic conditions such as cervical vertebral stenotic myelopathy (wobbler syndrome), equine
herpesvirus-1 myeloencephalopathy (EHM), rabies, and Lyme disease. Currently, the only definitive way for veterinarians to diagnose EPM is by identifying parasites in the brain or spinal cord during a necropsy.

Veterinarians typically diagnose EPM in horses by conducting SAG2, 4/3 ELISA testing, which is performed on serum and cerebrospinal fluid (CSF). They compare the antibody levels in the bloodstream to those in the CSF to see if CSF antibody levels are higher than expected compared to normal diffusion of antibodies from the blood. This would indicate antibody production in the central nervous system. Some practitioners might take cervical radiographs to check for spinal changes that appear more significant than expected with normal aging and could indicate another pathology as the cause of neurologic deficits.

Treating EPM in Horses

Veterinarians have several FDA-approved drugs available to treat horses with EPM: triazines and folate-inhibiting drugs. They also often recommend supplementing with vitamin E.

Researchers have suggested the triazines diclazuril and ponazuril both target the apicoplast organelle in S. neurona, which mammal cells do not contain.

Sulfadiazine and pyrimethamine are folate-inhibiting drugs used in combination to block folate synthesis in S. neurona, which it needs for survival. Researchers have reported vitamin E’s antioxidant properties can help protect the damaged central nervous system from oxidant injury.

With FDA-approved treatment, 57-62% of horses show improvement in clinical signs, but about 10% of horses relapse within one to three years of treatment.

Preventing EPM in Horses

Limiting opossum access to your horse’s feed and water sources remains one of the best ways to lower his risk of S. neurona or N. hughesi infection. Decreasing his stress levels and improving his overall health can also positively impact immune function, possibly lowering his risk of protozoal infection. In some situations your veterinarian might recommend intermittent treatment with low doses of diclazuril to reduce infections.

A Challenging EPM Case

In September 2020 veterinarians  at the University of Georgia’s School of Veterinary Medicine, in Athens, admitted George, a then-15-year-old Warmblood gelding used for dressage presenting with moderate neurologic deficits. A few days into his hospital stay, Katie Ellis, DVM, MS, Dipl. ACVSMR, clinical assistant professor, was brought onto the team.

In his case report George’s clinicians described him as bright, alert, and responsive on admission to the hospital. He was very ataxic in the hind limbs as he walked off the trailer and while being turned around in his stall, and in the hospital he dog-sat (a common sign of ataxia).

They also observed that George’s neurologic deficits were more pronounced in the hind limbs, especially on the right, than in the forelimbs. When his vets observed him on tight circles to both the right and left, they reported more significant gait deficits.

George’s clinicians performed cervical radiographs and SAG2, 4/3 ELISA testing to confirm their suspicions of EPM. The cervical radiographs showed only mild changes consistent with his age and work. His CSF analysis revealed high protein levels, which the veterinarians noted can be consistent with EPM infection, and serum titers confirmed their diagnosis.

Treatment and Rehabilitation

George’s veterinarians treated him with ponazuril along with sulfadiazine and pyrimethamine. “These drugs act by two different mechanisms to kill the protozoa and thus stop the parasite from inflicting further damage to the central nervous system,” they wrote in his report. “The gelding’s response to treatment has been positive, and his neurologic clinical signs have continued to improve since starting medication.”

In addition to medical treatment, Ellis and her team developed and completed daily rehabilitation exercises with George to help strengthen his muscles and improve his overall coordination. (See sidebar on page 33.)

Veterinarians employ physiotherapy as one of the first rehabilitation techniques for a neurologic horse, Ellis says.

Once George was stable standing on flat ground and able to pick up all four feet, Ellis used proprioceptive balance pads as the next step in improving his coordination and balance. “The horse should start with firm pads and only the front or hind feet on pads before moving to softer pads or placing all four feet on at the same time,” she says. Because this exercise can be very physically challenging for horses, she says she only incorporated it for short periods of time and increased the difficulty slowly based on George’s progress.

After George was stable hand-walking in a straight line, Ellis and her team started incorporating walking him in a serpentine pattern and over surface changes (i.e., from pavement to grass or arena footing).

George’s Future

University clinicians discharged George from the hospital after he underwent 28 days of treatment and rehabilitation. His owner continued his rehabilitation with guidance from and regular check-ins with Ellis. At his last recheck in 2021, George had progressed to light ridden exercise and was continuously improving.

Editor’s note: To protect the horse’s anonymity, we have changed his name in this article.

This article is from the Spring 2025 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.

Postpartum mares face a higher risk of developing large colon volvulus—a life-threatening type of colic in which the colon twists 360 degrees or more, cutting off blood flow and blocking the passage of gas and feed. Jesse Tyma, DVM, Dip. ACVS, a surgeon at Rhinebeck Equine, in New York, described the diagnostic and treatment approaches to this condition at the 2025 Cavalcade Education Equine Reproduction Seminar, held in Red Hook, New York, on Jan. 8.

Anatomy and Susceptibility in Postpartum Mares

Tyma described the large colon as a partially mobile gastrointestinal organ prone to displacement and twisting within the horse’s abdomen. The reason postpartum mares are especially susceptible to this condition relates to the empty space left in the abdomen after foaling, which allows the colon to shift more easily.

Diagnosing Large Colon Volvulus in Mares

The clinical signs of colic in a mare with large colon volvulus are usually severe, including vigorous pawing, violent rolling, a bloated appearance, and intractable discomfort. Tyma emphasized that prompt diagnosis and treatment are critical to the mare’s survival and foal’s safety.

“The colic exam aims to assess the postpartum mare’s overall health status, localize the lesion, and differentiate between a volvulus involving ischemia (lack of blood flow leading to oxygen deprivation and tissue death) and a displacement or other type of colic where the blood supply is unaffected,” said Tyma. “Diagnostics may include palpation per rectum, passing a nasogastric tube to check for gastric reflux, abdominal ultrasound to evaluate the colon wall and vasculature positioning, and bloodwork to measure lactate levels (which can signal severe tissue damage and the need for urgent intervention) and assess overall systemic health.”

Tyma also stressed the need to carefully assess the reproductive tract in the immediate postpartum colicky mare to rule out life-threatening hemorrhage, the clinical signs of which can overlap with those of large colon volvulus.

Treating Large Colon Volvulus in Mares

If a veterinarian strongly suspects large colon volvulus, the mare will likely need emergency colic surgery. “The goals of surgery are to characterize the lesion, manually correct the volvulus, and assess bowel viability to guide surgery decisions,” said Tyma. The surgeon might also perform a colon resection (the damaged tissue can be removed, and the healthy ends of the intestine stitched back together) or colopexy (creating an adhesion to the body wall to prevent future displacements and torsions), she added.

Postoperative Care and Complications

Beyond the risks of surgery and general anesthesia, recovery from large colon volvulus surgery involves intensive care because these mares often become systemically compromised and can decline quickly. “The postoperative patient requires close monitoring with serial examinations, multimodal pain management, fluid therapy, broad-spectrum antimicrobials, digital cryotherapy (icing the legs), supportive care, and a gradual reintroduction of feed,” Tyma said.

She added that common postoperative complications can include endotoxemia (toxin release into the bloodstream), diarrhea, recurrent colic, surgical site infection, and the painful hoof condition laminitis. “Transitioning the accompanying foal to a nurse mare is often recommended to lessen the physiologic demand on mares early in the postpartum period.”

Prognosis for Large Colon Volvulus in Mares

“In the best of clinical scenarios, the short-term prognosis for large colon volvulus is excellent, with survival rates reported up to 90%,” Tyma said. “However, in studies representing a broad population with variable referral access (to a surgical facility), the short-term survival rate is just 71%, with long term survival dropping to less than 50% by one year postoperatively. This speaks to the importance of quick referral and management for successful outcomes.”

Sixty-seven percent of mares treated for large colon volvulus produce at least one foal postoperatively. “The risk of recurrence of large colon malposition (inclusive of both surgical correction of displacement and volvulus) is 15%, and, following two occurrences of volvulus, the recurrence rate jumps to 80%, which is significant,” Tyma said. “Mares with recurrent volvulus that are intended to continue as broodmares should be considered candidates for a prophylactic procedure (colopexy or large colon resection) to reduce the risk of recurrence.”

Take-Home Message

Large colon volvulus presents a true emergency in postpartum mares, demanding rapid diagnosis, aggressive treatment, and intensive postoperative care. Tyma emphasized the importance of prompt referral to a surgical facility and potentially prophylactic procedures such as colon resection or colopexy in high-risk mares to reduce the risk of recurrence. “Prognoses for survival and continuation of reproductive careers can be good to excellent but remain dependent upon quick recognition of the condition, immediate action, and appropriate surgical and postoperative management,” she said.

Here’s how one veterinarian treated a particularly challenging case of this common skin condition

When Sarah Pell, DVM, of Genessee Valley Equine Clinic (GVEC), in Scottsville, New York, visited a regular patient in the height of mud season, she wasn’t surprised to find the 18-year-old Quarter Horse gelding had pastern dermatitis, also known as scratches, mud fever, dew poisoning, or greasy heel. The skin condition, which commonly appears on the heel bulb, pasterns, and around the fetlocks, is triggered by wet conditions, including mud, standing water, and damp bedding. Bacteria and fungi living in these conditions find their way into even the smallest cracks in the skin, creating an infection.

“Mud season,” which used to be confined to fall and spring in New York state, now often extends into January and February. Like most horses the practice sees, the gelding was on turnout during the day and brought into his regularly cleaned stall overnight for the winter months.

In consistently moist conditions and/or stalls that are not cleaned enough, it’s not uncommon to see horses with scratches, says Pell. There are many over-the-counter topical protocols that owners typically try prior to calling Pell and her colleagues at GVEC out for evaluation.

“We have conversations (with horse owners) about scratches mostly during annual wellness visits unless the scratches have become severe or cause secondary problems like infection, swelling, or lameness,” she says.

That was the case for this Quarter Horse. During his annual physical exam, his owner mentioned that the horse had developed scabby crusts on the pasterns of both hind legs.

“The crusts were moderate and did not appear to be super painful,” says Pell. “In severe cases, we have to sedate the horse to work on the lesions because the leg is so painful to the touch. When I see a case of scratches like this, one of the first steps is to clip away the hair surrounding the affected area.”

While scratches can appear in any horse, they are more common in breeds with heavy feathering. The excess hair traps moisture close to the skin, creating the prime conditions for pastern dermatitis to develop. Clipping the hair around the pastern and fetlock allows moisture to wick away from the skin and gives it a chance to dry out.

After clipping the hair, Pell instructed the owner to shampoo both hind legs daily for one week using Betadine scrub (dilute) or Selsun Blue medicated shampoo. For best results she advises letting the shampoo sit for 10 minutes on the affected area before rinsing. After seven days she told the client to continue the washing protocol two to three times a week for several weeks. She instructs owners to avoid picking at or pulling off the scabs despite how tempting it may be.

After cleaning the affected area and letting it dry thoroughly, she recommends applying Desitin, the cream used to prevent and treat diaper rash in babies, to create a barrier against moisture. Typically, after following this course of treatment, the condition should show signs of improvement within a month.

“It takes some time for skin conditions in all species of animals to clear up,” she says. “But call your veterinarian sooner if you notice the scabs spreading or the limb is swollen or painful.”

A Lingering Case of Scratches

Unfortunately, despite this horse owner’s efforts, the gelding’s condition worsened. His leg became painful to the touch and the lesions began draining. At this point Pell prescribed an oral antibiotic.

“At our clinic we make a topical ointment with a steroid that acts as a barrier, provides pain relief, and reduces inflammation,” she says. “There isn’t a universal topical out there for scratches (because) it’s very horse dependent.”

Pell also advised keeping the gelding in a stall for a minimum of seven days while continuing to do the shampooing protocol. Luckily, this was feasible, and he tolerated being stalled.

“Some people aren’t set up for stalling a horse, or the horse can’t tolerate it,” says Pell. “But in persistent cases, keeping horses out of the mud is ideal.” If a facility has an indoor arena, the horse can be turned out in that dry environment to alleviate some boredom.

A Long Road

Despite the horse owner diligently treating the scratches, they still persisted six months later. Since this gelding was older, she tested him for PPID (formerly known as equine Cushing’s Disease) to rule out systemic factors that could delay healing. The results were negative, so Pell’s next step was to remove some of the crust and submit it for a tissue culture to determine if a different antibiotic was necessary.

“There is no great way to treat scratches,” she says. “Even when treated very diligently, it may take several months to resolve fully.”

Fortunately for this particular horse, the scratches responded well to a different antibiotic. However, in rare cases pastern dermatitis can be so severe that it might even cause lameness or secondary cellulitis, says Pell. Cellulitis is an infection in the subcutaneous skin layer that often presents with clinical signs such as severe lameness and heat, swelling, and pain on palpation of the limb.

“A majority of these horses may have a fever as well,” she says. “If you notice any of these signs, call you veterinarian as the horse should be seen.”

When treating cellulitis it is important to reduce inflammation and control the infection, she adds. Your veterinarian might also treat your horse with a non-steroidal anti-inflammatory drug (NSAID) such as phenylbutazone (Bute) or flunixin meglumine (Banamine), and an antibiotic. Hydrotherapy is important in these cases to reduce the swelling, as well as hand-walking once the horse becomes more comfortable on the affected limb.

The Long-Term Prognosis

While pastern dermatitis can be inherently frustrating for horse owners, veterinarians say the long-term prognosis is typically favorable, and the horse usually can continue his lifestyle.

“Managing mud season is always difficult,” Pell says. “I always recommend getting the mud off the legs if a horse is on turnout, especially if they are coming in wet or muddy. Hose off the legs and towel dry, especially if the horse is more prone (to developing scratches), and apply a barrier like Desitin.”

Prevention might not be 100% possible, and scratches often occurs seasonally; however, Pell notes that checking your horse’s legs frequently and taking action early can help shorten the duration. “Look at your horse’s legs daily if you can,” Pell says. “If you notice something developing, even if it’s mild, keep a close eye on it and start getting those legs dry and clean. Give your horse time out of a wet environment for his leg to dry out. Don’t wait until it’s more of a problem because it’s much easier to resolve scratches in its early stages.”

Q: Can a nutritional imbalance or food allergy cause hives? My gelding broke out into hives after I started feeding him pure alfalfa hay, but when I switched him to Timothy grass hay the hives disappeared.

A: Owners often attribute itchy skin, hives, loose manure, and even behavioral changes as potentially being the result of food allergies, and they commonly presume alfalfa is the culprit. Whether these reactions are truly allergies—specifically food allergies—is often a point of debate. A food allergy is defined as an immune-mediated adverse reaction to food, where the body is reacting to a protein within that food or other substance, such as pollen. Allergies are reactions to substances that would not normally be problematic for most individuals.

Food allergies in horses do exist; however, most researcher and veterinarians consider them rare. If a horse has hives because of a food allergy, they would be expected to be all over the body rather than in isolated areas, which would point more toward a contact allergy from something like laundry detergent. The reaction might manifest as itchy hives or be solely in the gastrointestinal tract and result in clinical signs such as diarrhea.

Owners and veterinarians often reach for blood tests to diagnose allergies. These panels often include foods such as hays and common feed ingredients; however, research has shown that these tests are frequently inaccurate. The only true way to diagnose a food allergy is to do a withdrawal diet and then reintroduce the specific ingredients you believe the horse is allergic to. This takes time (often eight to 12 weeks) and dedication, and most owners are not willing to reintroduce ingredients that might be allergens, especially if the horse’s symptoms have resolved.

Horses can also have food intolerances or sensitivities, which are not immune-mediated reactions. They tend to present as loose manure and changes in behavior rather than hives, but hives could be present. Sensitivities might have a threshold such that the horse can handle the feed until consumed at a certain level. This is similar to lactose intolerance in people, where affect individuals might be able to consume small amounts of lactose in ice cream, but if they also eat a cheese pizza at the same meal, they show symptoms of their intolerance.

It is possible that your horse is not truly allergic to alfalfa and could handle alfalfa fed in smaller amounts, but a solely alfalfa hay diet causes issues for him. The only way to know whether that’s the case would be to add some amount of alfalfa back into the ration with the Timothy hay and see whether the hives return. This sensitivity threshold is likely why many horses can cope with supposed problem ingredients when they are in relatively small amounts such as in supplements but cannot cope with them when fed in greater quantities.

Another component of managing allergies is horses with allergies tend to be allergic to multiple things, such as insect bites and certain pollens. If you can control even a few of the allergens the horse is exposed to, you might eliminate or reduce allergic symptoms. So, if you can remove certain allergens that are easier to control from the horse’s environment, the horse might be able to handle exposure to other allergens, such as feed ingredients, without issue.

Q: I’ve always enjoyed giving my horse a warm bran mash in cold weather, but this doesn’t seem to be something people do much anymore. Is there still a place for wheat bran in my feed room?

A: Growing up I routinely fed a warm bran mash to my horse in the winter, especially on days when he worked hard. However it’s far more unusual now in part because we’ve realized that it might not be as beneficial as we once believed.

In my 1983 8^th Edition of the British Horse Society and The Pony Club Manual of Horsemanship it states that a bran mash is a “very useful warm food after hard exercise and hunting.” It goes on to say that after adding boiling water to the bran, you should add a generous amount of salt along with some oats, and then feed once cool. It finishes by saying “bran mash has a laxative value, and it has everything to recommend it when fed once a week to horses in work and to invalid horses. It is also a convenient way to administer medicines such as worming compounds.”

So how did a feed and feeding practice that were once so popular fall out of favor? To better understand that you need to understand your horse’s digestive tract, as well as the composition of the feed.

About Diet Changes and Digestive Tract Upset

Most of us are well aware that changes to a horse’s diet should be made gradually over several days. The reason for this is that the digestive enzymes, the amount secreted as well as the bacteria in the horse’s hind gut, are somewhat specific to the diet being fed. Therefore, if you change the makeup of the diet the enzymes and digestive bacteria must adapt, and this takes time. In the meantime if too much new feed is fed the horse might not be able to fully digest it and can lead to digestive disturbance (e.g., diarrhea, gas, and colic, etc.).

As previously mentioned, horse people used to routinely feed bran mashes once a week, largely for their believed laxative effect. Since becoming more educated in equine nutrition, it’s fascinated me that—while we take great care not to suddenly change a horse’s diet when starting most new feeds—this logic goes out the window when it comes to a bran mash. Essentially, when you feed a bran mash once a week you’re breaking all the guidelines you typically follow in keeping your horse’s diet consistent. The “laxative effect” might be because the feed change is causing digestive distress! This is probably not the best method of ensuring your horse’s digestive contents stay on the move.

Wheat Bran’s Nutritional Imbalance

Wheat bran has also fallen out of favor because of its high phosphorus level. In fact wheat bran has an inverted calcium to phosphorus ratio, meaning that it contains more phosphorus than calcium. This is actually common in traditional grains such as wheat, oats, and barley. However, wheat bran is particularly high with a phosphorus content of about 1% and calcium at only 0.15%.

Researchers realized feeding diets with a lot of wheat bran increased the risk of developing secondary hyperparathyroidism, a condition that results from a calcium imbalance potentially caused by horses consuming a diet too high in phosphorus. “Big head” or “bran disease” was far more common when horse owners and managers fed traditional grains and wheat bran more commonly than we do today. In reality this condition is unlikely to result from feeding a bran mash once a week. It’s far more likely if bran or traditional grains are fed daily in a poorly balanced ration. Traditionally any number of unfortified grains could have caused a similar issue, but because, proportionally, brans add much more phosphorus per pound than the grains, they are often considered a larger problem. With the concern over big head and potential links to bran, much less wheat bran is now fed and most rice brans are fortified with additional calcium carbonate to neutralize the problem.

So, What’s Right About Bran?

Going back to the quote from my Manual of Horsemanship, if a bran mash has “everything to recommend it,” what’s it doing right, given the two already discussed areas of concern? First, the manual hints that bran mashes are generally welcomed by even the most picky eater. Often, after very long and heavy work such as fox hunting, horses might have a reduced appetite and the goal is to get the horse eating and the digestive tract moving. Some sick horses that have gone off feed can be tempted to eat with a bran mash. Therefore, a bran mash can be a very useful tool when faced with a horse that has gone off feed and will not eat anything else.

Second, adding salt to a bran mash is a great practice, especially when fed after work that might have incurred heavy sweat losses.

Alternative Warm Mashes for Your Horse

So, when you want to give a bran mash is there something else that might be more beneficial? Is there a better way?

If you already give your horse supplemental feed, whether it is pellets or a textured feed, add hot water to make a warm mash just as you would with wheat bran. This way you are creating the mash but using familiar feeds that are less likely to irritate the gastrointestinal tract.

If you only feed forage, purchase some hay pellets that are like the forage you feed and use them to make a mash.

Next add some salt, or if you already give salt every day and your horse has been sweating heavily, add an electrolyte. If you need to entice a picky eater or a horse that has gone off feed, try adding carrot or apple peelings. If you have your heart set on a weekly bran mash, then I suggest adding a small amount of bran to your horse’s every day feed so that the mash is not a novel feed to your horse’ digestive tract. But be careful to keep the amount of bran small and consider discussing with an equine nutritionist how to add bran to your ration while maintaining a balanced mineral profile.

Q. I feed my ulcer-prone horse alfalfa before riding, because I’ve heard the calcium in alfalfa works like a big Tums antacid to keep my horse’s stomach from hurting during exercise. I was recently told that alfalfa pellets don’t work and that I should use alfalfa hay or chop instead, because the alfalfa needs to create a “hay mat” in the stomach to keep acid from splashing up into a horse’s esophagus (basically, causing horse heartburn). Is it true that I need to feed alfalfa hay or chop instead of pellets?

A. You are correct. Alfalfa is typically high in calcium, which researchers have shown reduces stomach acidity due to its buffering capacity. In a study at Texas A&M University, 12 horses were assigned to one of two groups: a 1:1 ratio by weight of Bermuda hay and a concentrate feed or of alfalfa hay and the same concentrate feed.

Treatment periods lasted 28 days before horses switched to the other diet with a 21-day washout period between treatments. At the start of the study each horse went through a gastroscopy to determine whether they had gastric ulcers and, if so, their severity. Horses were rescoped after the 28-day treatment periods to determine whether any existing ulcers had improved or worsened or new ulcers had appeared.

The researchers found that ulcer severity scores were significantly lower when horses ate alfalfa hay compared to Bermuda hay. Feeding alfalfa prevented ulcer formation in 11 of 12 horses that did not have ulcers initially, whereas only three of the 12 horses that did not have ulcers stayed ulcer-free when fed Bermuda. The team attributed these results to alfalfa’s higher calcium and protein content providing greater buffering capacity. The complex carbohydrate fractions found in alfalfa’s cell walls have also been shown to provide better buffering than those found in grass hays.

It’s clear that alfalfa does a good job of buffering the acid in the equine stomach. The question therefore becomes, does it matter what form the alfalfa is in? Long-stem hay requires a good amount of chewing before being swallowed, and chewing results in saliva. Equine saliva contains a good amount of sodium bicarbonate, which will also buffer stomach acid. Pellets take less chewing so result in less saliva and lower buffering from the bicarbonate. So long-stem hay would be preferable from that perspective. But what about the fiber mat?

The equine stomach is not completely full of acid. Large feed particles float on top of the acid, helping prevent it from splashing into the upper portion of the stomach where most ulcers occur. Pellets have a much smaller particle size than long-stem fiber, so alfalfa hay is more likely to make a better mat than pellets. Keep in mind that any forage in hay form—not just alfalfa—will form a good mat and cause saliva production. So if your horse has eaten hay within the few hours prior to your ride, he likely already has a good mat.

The calcium in pellets might buffer more quickly than hay due to the smaller particle size, but the smaller particles might also cause the calcium to move out of the stomach faster than larger particles would. So the question becomes: Which is more important, the hay mat or the buffering? If the stomach’s acidity is low, it won’t matter as much if the acid splashes into the stomach’s unprotected upper region. A hay mat is less important when the stomach acid is less acidic, and depending on when your horse last ate hay, a mat might already exist.

If you’re arriving to ride your horse and he has an empty stomach, and you give him alfalfa while you’re grooming, he might not have time to consume much alfalfa hay, because it requires more chewing. You might get greater buffering capacity more quickly by feeding pellets, although you won’t get a great mat. Most stomach buffers are relatively short-lived, lasting at most a couple of hours. Research has shown that some commercial buffers on the market buffer effectively and more quickly than alfalfa. These can be great options when given before exercise, if you need buffering capacity quickly.

Alfalfa’s ability to help reduce ulcers, and in which form you should use it, depends on a combination of complex interactions. The best solution for each horse might not be completely clear, but what we do know is that giving some form of alfalfa before riding a horse with an empty stomach will likely have a positive impact and could reduce your horse’s risk of developing gastric ulcers.

Equine metabolic syndrome (EMS) is a complex condition that involves insulin dysregulation (ID), obesity, and an increased risk of laminitis. Horses with EMS often need a multifaceted management approach to improve their quality of life and prevent serious complications. These five key management changes can help you improve your EMS horse’s metabolic status and overall well-being.

1. Optimize Diet and Forage Selection for EMS Horses

Diet plays a crucial role in managing horses with EMS. “Diets high in nonstructural carbohydrates are a risk factor for development of insulin dysregulation, a key component of EMS,” says Katie Wilson, DVM, Dipl. ACVIM-LAIM, clinical associate professor of large animal internal medicine at the Virginia-Maryland College of Veterinary Medicine, in Blacksburg, Virginia.

“One of the simplest and biggest changes owners can make is actually weighing the amount of concentrate and forage their horses are eating per day to better control caloric intake,” says Wilson. Grass hay with an NSC content of less than 10% is ideal for horses with metabolic problems, she adds. If the NSC content is unknown or higher than 10%, soaking the hay for at least 60 minutes (and discarding the soak water) before feeding can make it safer for EMS horses.

Avoid feeding your EMS horse concentrates unless absolutely necessary, Wilson says. However, forage-only diets do not provide all the vitamins and minerals (i.e., sodium, chloride, copper, zinc, Vitamin E, and selenium in areas with selenium-deficient soil) horses require, so they need a ration balancer if the diet is forage-based, she adds. “Some ration balancers are high in NSC, however, and can induce an exaggerated insulin response after feeding, so ingredients or individual horse response to feeding should be evaluated.”

2. Implement an Effective Exercise Routine

Exercise also plays a crucial role in managing EMS. An effective exercise routine can help horses safely lose weight (if needed) and improves insulin sensitivity. Always work with your veterinarian when creating an exercise plan for horses with a history of laminitis to avoid exacerbating the condition or unknowingly cause pain, says Wilson. Horses recovering from laminitis should only exercise after veterinary clearance.

After a laminitic episode and once cleared, Wilson recommends gradually introducing physical activity, such as five minutes of walking followed by 15 minutes of trotting, repeated five times per week. For EMS horses without laminitis, moderate exercise, such as trotting and cantering for at least 30 minutes, five times per week can benefit their insulin sensitivity.

3. Monitor EMS Horses’ Body Condition and Weight Regularly

Horses with EMS often display generalized or regional adiposity, but even horses with a normal body condition can have ID, says Wilson. Regularly assess your horse’s body condition to ensure he remains a healthy weight. “Assessing body condition score every two weeks can help to quantify changes that might not be noticed,” she explains. “Assessing body weight can be helpful as well, by either using an equine scale if one is accessible, or a weight tape.”

“Reducing body condition (if warranted) has been shown to improve insulin sensitivity, and weight reduction can help decrease the forces in the foot that result in sinking or rotation in horses with laminitis,” adds Wilson.

4. Adjust Turnout and Grazing Practices for EMS Horses

Unrestricted grazing can harm EMS horses because pasture often contains high levels of sugars and NSCs. “Free-choice grazing should be restricted in horses with EMS and (a history of or active) laminitis,” says Wilson. She suggests turning affected horses out in a dry lot or small paddock with little to no grass or using a grazing muzzle or strip grazing to limit pasture access.

“If horses need to be reintroduced to grazing after laminitis has resolved, it should be done slowly and blood insulin concentrations should be measured regularly to assess the horse’s insulin response to the added carbohydrate content of the grass,” says Wilson.

5. Work Closely With a Veterinarian

Equine metabolic syndrome involves many changing factors, so work closely and regularly with your veterinarian to ensure effective management. “One common mistake is assuming that a one-time change in management or feeding practices will fix the problem,” says Wilson.

Regular examinations and blood insulin monitoring can help your veterinarian tailor management strategies to the horse’s specific needs. Your vet needs to assess your horse’s insulin levels after dietary changes or modifications to his grazing schedule and at different times of year because season can impact insulin sensitivity, adds Wilson.

Equine practitioners also play a crucial role in helping horse owners navigate logistical challenges and develop practical, individualized management plans. “Veterinarians understand that there are usually many logistical limitations to implementing the ideal changes recommended for a horse with EMS and are happy to work within the owner’s restrictions to develop a plan that will work best for an individual horse,” says Wilson.

Take-Home Message

Managing a horse with EMS takes a proactive, tailored approach that fits the horse’s specific needs. By making key changes to diet, exercise, body condition monitoring, and turnout strategies—while increasing veterinary collaboration—owners can significantly improve their EMS horses’ health and well-being. Equine metabolic syndrome has no cure, but consistent monitoring and adjustments can go a long way in preventing laminitis.

Check off all the items on this list to be ready for a healthy, successful riding season

Springtime—a season we look forward to as equestrians. Riding arenas emerge from their snowy blankets. The sun shines longer and brighter every day. Much-awaited shows and competitions are right around the corner, and we’re eager to shift things into the next gear.

Full of potential, the spring months set the tone for the rest of the year. The key with transitioning from winter to spring is to have a plan in place to tackle your horse’s various seasonal needs. You should think about vaccinating and deworming, of course, but also about rebuilding your equine athlete’s fitness after a winter hiatus.

There’s a lot to accomplish transitioning into spring, so let’s get organized with a checklist:

• Physical exam;
• Bloodwork (if recommended by your veterinarian);
• Dental exam;
• Fecal egg count;
• Deworming;
• Spring vaccines—core and risk-based;
• Body clipping (if applicable);
• Sheath cleaning;
• Blanket and tack maintenance/repair;
• Saddle fit evaluation;
• Diet evaluation;
• Spring cleaning and sanitizing;
• Coggins test; and
• Health certificate (aka certificate of veterinary inspection, or CVI) if your horse travels.

The Essentials

Physical and dental exam

“Springtime is a great time to get your equine partner all checked out and ready to roll for the summer,” says Sarah Cohen, DVM, owner of Equity Performance Equine, an ambulatory veterinary practice based in Wellington, Florida. “During a routine annual physical exam, your veterinarian can look for any unnoticed issues in your horse’s heart, eyes, feet, or gastrointestinal tract. This is also an excellent time to perform an oral exam to assess the need for teeth floating as well as identify any fractured teeth or other oral health issues.”

Vaccines

Spring vaccines are a routine part of wellness exams. All horses in the United States should receive the four core vaccines—rabies, tetanus, West Nile virus (WNV), and Eastern/Western equine encephalomyelitis (EEE/WEE)—and then get boosted annually. These boosters are generally given in the spring to maximize protection against WNV/EEE/WEE when mosquitoes, which spread these diseases, emerge in early summer.

Beyond these four, different geographical areas present different equine infectious disease challenges and, therefore, require different immunization protocols. “Veterinary practitioners in your specific areas will know best how to advise you regarding risk-based vaccines and guide you with respect to the needed frequency of vaccination,” Cohen says.

Regions with year-round hot and humid climates—Cohen’s Florida being a prime example—have the added challenge of persisting mosquito populations, warranting biannual vaccination against WNV and EEE/WEE.

In addition to geographic risks, you must consider farm-specific risks. Facilities housing broodmares or frequently traveling show horses, for example, need to provide their horses additional protection (immunization) against influenza and equine herpesvirus (EHV).

Parting words from Cohen about vaccines: “They are safe and inexpensive. Treating a vaccine-preventable disease is both costly and heartbreaking.”

Parasite control

Internal parasites can damage your horse’s internal organs, especially those of the digestive tract. Equine parasitic burdens vary based on the age of the individual, geographical region, and herd immunity, says Constance Gorman, DVM—hence the importance of consulting your veterinarian when formulating a parasite control plan. Gorman is a field care associate at Hagyard Equine Medical Institute, in Lexington, Kentucky, and an FEI treating veterinarian.

The first step in parasite prevention is performing a fecal egg count (FEC) in the spring and fall to see what types of parasites might be living inside your horse, our sources say. When possible, Gorman does an FEC before deworming and again two weeks later to measure the dewormer’s efficacy, a process known as a fecal egg count reduction test.

Identifying and quantifying your horse’s internal parasitic load—rather than deworming willy-nilly—is key to slowing the dewormer resistance problem caused by indiscriminate administration of anthelmintics over several decades. “Individual FEC also allows more informed and more targeted deworming, thus increasing the effectiveness of each treatment,” says Cohen.

The FEC is not foolproof, however. “Tapeworm eggs can be difficult to find, so I recommend deworming every horse at least annually with praziquantel regardless of FEC results,” says Gorman.

Springtime Challenges

Skin issues

April showers bring May pastern sores. When snow melts into mud, many horse owners find themselves dealing with scruffy skin. Damp conditions and long haircoats can leave skin, especially on the legs, at the mercy of trapped bacteria and fungi.

Dermatophilosis (aka rain rot) is a common diagnosis. When caught early, you can usually resolve this skin infection with a couple of thorough scrubby baths, says Cohen, mixing a small amount of dilute povidone-iodine with the shampoo. “In some rare cases of severe dermatophilosis, antibiotics may be prescribed to combat the infection,” she adds.

“With dermatophilosis and similar conditions, daily nursing care is often necessary,” says Cohen. “Otherwise, recurrent skin issues can result in painful sores or even lameness.”

She and Gorman share tips for protecting your horse’s legs from mud and the skin issues it can cause:

• Keep the hair around the pastern clean and dry by brushing or toweling off dirt.
• Dry and groom your horse after heavy rain to reduce bacteria and fungus buildup on the skin.
• Apply ointments only if recommended by your vet, as gooey substances can trap bacteria near the skin.
• Pick your horse’s feet daily to remove rocks packed in with the mud and to check for and manage signs of thrush.

Hoof issues

“Thrush is caused and exacerbated by damp environments common during the spring season and sometimes also by poor hoof hygiene,” Cohen says. “If meticulous hoof care and over-the-counter treatments don’t work or if your horse is footsore or lame, it’s time to call your veterinarian.”

“Additionally, during the spring season hoof growth increases, so farrier upkeep is more important than ever,” Gorman says. “If the hoof has had a chance to overgrow and there are some cracks or separation along the white line area, this gives bacteria a chance to invade the foot and cause painful hoof abscesses.”

Spring grass and diet

With lush spring grass, keep two things in mind: disease prevention and grazing in moderation. Spring is a precarious time for equids prone to obesity, metabolic dysregulation, and the hoof disease laminitis.

As your veterinarian will tell you, limiting metabolically challenged horses’ nonstructural carbohydrate (NSC) intake is essential. Grass consumption can aggravate conditions such as insulin dysregulation, equine metabolic syndrome, and pituitary pars intermedia dysfunction (PPID, formerly equine Cushing’s disease). That’s mainly because fresh grass contains large amounts of the NSCs starch and sugar.

“Grasses, which are naturally high in sugar, generally have an even higher sugar content in the spring and fall,” Cohen says. “And the sugar content in grass actually increases through the day, so the safest time to graze at-risk animals is in the early morning hours.”

Unfortunately, with certain horses, being selective about timing isn’t enough. “For at-risk individuals, it’s safest to stay off the grass entirely,” Cohen says. If that’s not an option, she recommends using a grazing muzzle when putting vulnerable equids on pasture. Research shows that properly fitted grazing muzzles reduce grass intake by 78-83% (Longland et al., 2012), making them safe and effective grazing moderation tools. You can also feed hay, of course, but recognize it contains NSCs that you might need to soak away before feeding.

Prioritize prevention, and don’t wait for the arrival of spring grass to take the steps necessary to keep your horse safe. Starting in late winter, Cohen recommends asking your veterinarian to pull blood and check on your horse’s metabolic status. The goal is to determine if you need to adjust medication, diet, and/or management tactics.

On the topic of nutrition, spring is a good time to consider whether your horse’s diet is still meeting his needs. If his workload has fluctuated over the past few months and/or if his weight or energy levels have changed, take a fresh look at what goes in his feed bucket. “Steady increase in proper caloric intake may be necessary as your horse begins to work in higher intensity during the spring,” Gorman says. Your veterinarian or nutritionist can advise you when reevaluating feeding plans for horses in your barn.

Haircoat and body clipping

With both ambient temperatures and riding time on the rise during spring, we sometimes find ourselves sliding off sweat-soaked mounts that take hours to dry. Shaving away that bothersome winter coat is an appealing solution, albeit a controversial one.

“Many factors will affect whether body clipping is the best thing for you and your horse,” Gorman says. “Location and weather—especially humidity—breed of horse, discipline, and level of work are all important elements to consider.”

If a horse is in an intense training program, she says she has no qualms about body clipping if the owner is aware of the precautions they must take during inclement weather. “I would not, however, body clip past February or March because that could affect your horse’s summer coat that is coming in as he sheds,” Gorman says. “That’s of course excluding horses with PPID, for which clipping year-round may be necessary to maintain comfort.”

The main point is the choice to body clip will depend on individual circumstances affecting you and your horse.

Bringing Your Horse Back Into Work

With bitter weather and limited daylight during winter, many of us opt to take a break from riding. If you’re one of those riders, you certainly know bringing horses back into work from a period of rest requires preparation and patience.

Gorman walks us through her protocol: “If an equine athlete is starting back from several months off, I do recommend having your veterinarian perform a basic flexion exam. Ensuring that tendons, ligaments, and joints haven’t sustained any damage before starting work again will set you up for a successful comeback.”

She and other experts agree that taking things slowly when working back up to previous athletic ability is a must. “Walk and trot large circles,” she says. “Ride up hills. Do five to 10 minutes of supple walking and bending between trot intervals. Ride in shorter trot/canter intervals for the first few weeks as your horse is regaining both cardiovascular and musculoskeletal fitness. And don’t forget to give him breaks. Recovery is just as important for muscle conditioning as is the actual work.”

As fitness increases, so does muscle mass. Bulkier muscles could translate to altered saddle fit, so reach out to a professional saddle fitter if your horse shows signs of discomfort through his back as you return him to fitness.

Final Step: Spring Cleaning

Now that you’ve checked all the horse care items off your list, it’s time to prepare your horse’s living environment for the new season ahead. The past two years spent navigating life through a pandemic have taught us more than most care to know about sanitation and biosecurity.

As warmer weather rolls around, take the time to perform a deep spring cleaning of your barn and equipment. Run blankets through the washer, soak your grooming brushes in disinfectant, and scrub that muck off the stall walls. Whether we’re talking about thrush or EHV, good hygiene is a key part of disease prevention.

Take-Home Message

Your horse has individual needs. To keep him protected and healthy, you must provide him with the right care at the appropriate times. Full of changes and challenges, spring is an important season to stick to the preventive health care plan devised with your veterinarian. By being diligent about vaccinations, deworming, diet, and other routine necessities, you can do your part to ensure your horse has a long and productive life.​

Skippy was almost aptly named. He didn’t skip, but he did hop and jump. And to his owner’s great regret, Skippy bucked.

“He was a horrible ride,” recalls Amber Cash of Newark, Delaware. “He kicked, he bucked, he bit, he would run and not stop. I thought I could train it out of him, but he always seemed angry.”

Skippy wasn’t always like that, though. Often—and especially when he didn’t have a rider—the big red gelding was delightful, which made Cash suspect his bucking was pain-related. “He was loving, funny, smart, and playful,” she says. “But when he hurt, he was a holy terror.”

Cash tried dozens of saddles, stretching techniques, and chiropractors, all to no avail. It wasn’t until she got his back radiographed that she discovered the tips of her horse’s backbone were running into each other—a condition known as kissing spines. After surgery to create more space between the vertebrae, Skippy was a changed horse. “He was so much happier and easy to ride,” says Cash.

Bucking Basics

The buck evolved in horses as a defense mechanism to literally throw off predators, says Sue Dyson, MA, VetMB, PhD, an independent consultant in the UK, who published a scientific review on bucking research in 2021.

A few other herbivores, such as sheep and antelope, have a certain kind of buck, she says. But the equine buck takes the skill to new heights: Their leaps into the air, with two or four legs off the ground, sometimes combined with either an arched-up or stretched-out back, the head low, and/or sudden stops and twists, could pitch off just about any animal—­including humans.

What Kind of Buck Is It?

Not all bucks are created equal, says Dyson. Some include little hops with the upper back—the thoracic spine, from the wither to the loin—in extension and the head up; some involve full flying leaps with the back up and the head down (“pronking” or “crow-hopping”); some propel rapidly forward in a series of pronks (“bronking”), often with lots of stops and twists.

“I always ask my clients, ‘Do you feel the horse is trying to buck you off?’ ” Dyson says. “If they say no, that’s a completely different situation from the horse that does the kind of rodeo act when its back is in flexion all the time.”

Our sources agree that most horses that buck consistently merit a visit from the veterinarian. Even if your horse isn’t throwing you off, his body language is likely telling you something’s wrong, and he needs help.

We’ve listed nine reasons horses buck—most of which are pain-related. Bucking seems to be a natural equine response to pain, although the biological reason for that remains unclear. “We can’t necessarily say it’s pain relief, but it’s definitely a reaction to pain,” says Dyson.

1. Kissing Spines

When the long points sticking up from the top of vertebrae—known as spinous processes—crowd each other, they’re said to be “kissing.” Bone hitting bone is painful, especially with added pressure from a rider, says Beau Whitaker, DVM, of the Brazos Valley Equine Hospital, in Salado, Texas. “The No. 1 thing I look for in bucking horses is kissing spines,” he says.

Kissing spines in the saddle area (the caudal thoracic and the lumbar spines) are the most likely to cause discomfort that can lead to bucking, he says. “When you get on the horse, it causes the back to drop and the spine to ventroflex (extend), and that pushes those bones even closer together, causing more pain, so the horse starts to buck.”

Not all horses with radiographic evidence of kissing spines, however, display signs of pain such as bucking.

2. Sacroiliac Joint Pain

The large, rigid sacroiliac joints lie between the ilium of the pelvis and the sacrum (the vertebral column from the loin to the tail—also considered a part of the pelvis) and are supported by ligaments above and below. Through wear or injury, horses can damage these joints and ligaments—and the result is often a very telltale kind of buck, says Dyson.

“They usually only buck when ridden, not on the longe,” she says. “They buck with their back extended, most commonly in canter, and may kick out backward or sideways. As a rider, you don’t feel like they’re trying to get you off.”

Her recent postmortem work for a soon-to-be-published study has shown that some of these horses even have a damaged obturator or sciatic nerve, which could lead to neuropathic pain (caused by damage to specific nervous system regions that perceive pain).

3. Gastric Ulcers

Bucking-related pain can also come from the stomach, says Whitaker. Sixty to 90% of adult performance horses have gastric ulcers, which develop when digestive acids break down the stomach lining, often due to stress, large amounts of concentrate feeds, and/or long breaks between meals.  

“Some horses get enough pain from gastric ulcers that when they’re moving, especially cantering, that acid starts to splash around and irritate them, making them buck,” he says. Gastroscopy is the only way to confirm a horse has ulcers, so it’s a useful procedure when other pain has been ruled out.

4. Poorly Fitting Tack

A saddle that’s incorrectly fitted or badly positioned on your horse’s back can concentrate high pressures in a small area or pinch, such as just behind the withers, Dyson says. Some horses have a “bucking spot” behind the saddle: Firm pressure to this area might trigger bucking.

A broken tree can also cause a horse to react, says Whitaker, as can a poorly fitted saddle pad or tack such as breastplates, bridles, and bits.

Girths can also be culprits, says Dyson, particularly those with elastic inserts. Some horses might find the moving elastic uncomfortable.

5. Other Sources of Pain

Bucking-associated pain can come from all over the body, our sources say. For example, they’ve found it in the pelvis, limbs (especially the hocks and stifles), and ribs. “Lameness may be the cause of bucking,” says Dyson.

Or it might come from the other end of the horse: “Sometimes they’ll have a hook or a fractured tooth,” says Whitaker. “This can hurt more when they get their heads in a certain position. Often those horses will throw their heads, but we do see some that manifest in ways you wouldn’t expect, like bucking.”

Dyson says she has seen bucking related to a torn ligament in the back, spondylosis (degenerative bone changes) of the spine under the saddle, and a broken sternum, among other orthopedic issues.

6. Fear

In some circumstances, the consequences of a horse’s buck—namely, the rider falling off—can scare them. “You see some horses, when they’ve bucked the rider off, they just stand there and act absolutely astonished and fearful,” Dyson says. “They are often terrified of being remounted, (and they may especially) not tolerate the rider sitting upright.”

This doesn’t mean the horse is afraid he’s “done something wrong,” which is too anthropomorphic, she says. Rather, the horse is fearful of having a mass projected over its head.

7. Accidental Buck Training

Whether they’re frightened or anticipating pain, or they just don’t like being ridden—maybe due to previous bad experiences—some horses learn that strong bucking gets rid of the rider and any related pain. That relief is a strong reward, and they learn to buck to get it.

Even after veterinarians perform therapy to relieve a bucking horse’s pain, he might continue to buck because he learned to when it hurt to be ridden. “Unless something changes, like an intervention from a behavioral management point of view, you may get into a situation which spirals out of control,” Dyson says.

Unskilled riders can start the spiral, she says. Riders with poor balance might bounce a lot (causing pain) and eventually fall with a simple buck. And some horses develop a tendency to buck early in a riding session, which could be the result of having quickly dislodged novice riders.

Learned bucking is often more difficult to resolve than pain-related bucking, our sources say. “Sometimes you have to try to work those horses through the mental aspect of it, once you get past the pain aspect,” Whitaker says. “And that’s not always easy to figure out.”

8. Intentional Buck Training

It’s worth mentioning, of course, that some horses are purposefully trained to buck. “Certain lines of horses, from a rodeo performance point of view, are apparently better at bucking,” Dyson says. Usually, when they don’t have cinches around their groin, they won’t buck, she adds. However, they might have a greater propensity for it.

Meanwhile, some high-level dressage horses, such as from the Spanish Riding School in Vienna, Austria, are taught bucklike movements such as the capriole.

9. Feeling Great!

Bucking can represent both negative and positive feelings. Horses buck out of exuberance when galloping and playing at pasture and sometimes under saddle, says Dyson. “They can feel fresh and exuberant, like when you take them out to the beach to gallop, and they give some happy bucks,” she says.

There’s a stark difference between the happy buck and the buck that says something’s wrong, however. Feel-good bucks are usually one-shots in specific situations of excitement, whereas bucks in a series or that happen every time you ride should raise a red flag.

Happy bucks aren’t usually an issue—unless you’re not skilled enough to ride them out, Dyson says. However, horses can be trained to not buck under a rider, even when they’re exuberantly happy.

Getting an Evaluation

If you’ve got a bucker, get your horse—and your tack—evaluated. Have a master saddler check your saddle and bridle, and ask your veterinarian to run a buck evaluation. That usually starts with palpating the back to check for reactions to pain, followed by radiographs and, if necessary, a gastroscopy, says Whitaker.

Veterinarians should also evaluate the horse in hand, while longeing, and under saddle (if he’s safe to ride), says Dyson. Local (temporary) nerve blocks can help find the part of the body that’s hurting.

Sometimes veterinarians perform an ultrasound of a painful area to see if the soft tissues have been affected. If those checks don’t lead them to the problem, practitioners might pursue bone scans (scintigraphy) to look for inflammation in the bones. Bone scans can help veterinarians track improvement once horses have started therapy, Whitaker says.

Treatment must be targeted depending on the diagnosis, says Dyson. Most horses also need behavioral retraining after they’ve recovered physically, to learn not to buck once the pain is gone. Seek the help of a certified behaviorist or a trainer versed in positive reinforcement methods.

Take-Home Message

Bucking might be what happy horses do in a field, but it can spell trouble when they’re doing it repeatedly under saddle. Veterinary treatment and behavior management can help resolve the issues behind the buck, our sources say. And when you identify the reason for the buck—like Cash did for Skippy—it can be a game-changer for both horse and owner.

Orthobiologics is a term encompassing a range of biological therapies that help a horse’s body repair itself from acute injury or chronic conditions such as osteoarthritis (OA). These therapies offer better long-term solutions than products that can cause complications when used over an extended period, said Beau Whitaker, DVM, CERP, of Brazos Valley Equine Hospitals in Salado, Texas, at the 2025 IGNITE Sports Science for the Olympic Disciplines Seminar, held Jan. 12-13, in Ocala, Florida. 

Deciding on an Orthobiologic for Use in Horses 

How do veterinarians decide which orthobiologics product to use? Typically, they look to their own and others’ anecdotal experiences, peer-reviewed research (mostly in humans), research or data provided by a company, and client preferences. 

Other factors veterinarians consider when deciding on a specific product include: 

1. Time frame 
   • What is the horse’s competition schedule? 
   • What is the withdrawal time of the product (i.e., how long before competition must the treatment be administered to comply with regulations)? 
   • Is the horse hurt or injured (versus giving an injection for maintenance purposes)? 

2. The effect relative to diagnosis 
   • Is the issue with soft tissue, the joint, or both? 
   • How severe is the injury/condition? 
   • How old is the horse? 

The ideal dosage for many orthobiologics remains unknown. Whitaker said veterinarians make the decision relative to joint size and pathological severity as well as anecdotal experience. To date there isn’t “clinical data evaluating dose response relative to product and condition treated,” he added. 

Orthobiologics for Equine Asthma 

In the second part of the discussion on orthobiologics, Dan Dreyfuss, DVM, MA, of D. J. Dreyfuss DVM LLC Consulting, in Hampstead, Maryland, spoke about using orthobiologics for respiratory diseases. 

Researchers conducted a small pilot study to look at the initial safety of nebulizing orthobiologics. Eight horses with mild asthma were evaluated and assigned a baseline weighted clinical score (WCS) based on nine respiratory-related clinical signs. They then received a series of six nebulizations at 48-hour intervals. The practitioners saw no significant safety issues, and seven out of the eight horses improved their WCS. 

Next came a larger pilot study where researchers repeated the same administration and evaluation protocol as in the initial safety study. Thirty out of 34 horses (88.2%) demonstrated a positive response to orthobiologics through nebulization. Results from these small studies are enough to encourage researchers to perform a larger study, said Dreyfuss. 

Take-Home Message 

“Orthobiologics are moving us in the right direction,” said Whitaker. Questions remain about the clinical data, required dosages, and product safety. 

Dreyfuss said it’s early in the process of using orthobiologics for horses with asthma, but he is encouraged by the significant clinical improvement in a large percentage of horses in the pilot study. 

With more time and research the different roles of orthobiologics in horses will become clearer, he added. 

Q: My horse has recently been diagnosed with EOTRH and needs some teeth removed. What can I do to support him nutritionally through this process?

A: Dental health problems in horses can be stressful to manage, but working closely with your veterinarian for medical care and considering how to support your horse nutritionally is a great start. Equine odontoclastic tooth resorption and hypercementosis (EOTRH) is a progressive and painful dental condition that primarily affects the tooth roots and surrounding gingiva (gums) in older horses. While the exact cause of this condition remains unknown, multiple factors likely contribute to its development.  

The treatment for EOTRH depends on the stage of disease. For mild cases your veterinarian might recommend more frequent dental examinations, pain management medications, or dietary modifications. As the disease progresses, surgical removal of teeth (typically incisors) and affected tissues might be necessary.  

When a horse has dental issues, evaluate his diet to ensure he can comfortably consume his feed and water. Make sure his roughage requirements are met and that he doesn’t have extended fasting periods.  

Adequate Roughage Intake for EOTRH Horses 

Horses have evolved to consume a fibrous diet with small frequent meals throughout the day. The severity of EOTRH and the number of teeth removed will determine what the horse can comfortably consume.  

A horse’s diet should contain a minimum of 1.5% of his body weight in forage daily. Whenever possible keep a portion of the horse’s diet as long-stem fiber to promote gastrointestinal health.  

Even after the removal of some teeth, horses often return to eating hay. Most can use their lips to eat grass and can grind forages with the molars. When they horse is not able to comfortably consume and chew the long-stem fiber, you need to introduce processed fiber sources . This could be chopped hay, hay cubes, beet pulp, or a complete feed. 

Nutritional Management Before and After Equine Dental Surgery  

When you schedule your horse’s dental surgery, it can be beneficial to add a fiber source that will be easy for your horse to chew. Make feed changes slowly. If your horse currently consumes hay but will be on mashes during his surgical recovery period, add some of those mashes into his program before surgery. This ensures the mash choice is palatable for your horse and his gastrointestinal tract has time to adapt to the changes.  

For example, if a 500 kilogram (1,100 pound) horse consumes 2% of his body weight in hay daily (10 kg or 22 lb), gradually introducing 1-2 kg (2-4 lb) of soaked hay cube mashes before dental surgery can help him adjust. Your dental surgeon can provide more detailed recovery instructions.  

Managing Severe Cases of EOTRH 

In severe cases where the horse can no longer consume hay and pasture is unavailable, designing a safe nutrition program can be challenging. In these cases use a combination of chopped fiber sources and complete feeds, which should be soaked and fed at a rate of 1.5-2% of the horse’s body weight per day (e.g., 16-22 lb for a 1,100 lb horse). 

To maintain digestive health and prevent long fasting periods, divide the daily feed amount into four to six small meals spaced no more than four to five hours apart. Soaking the feed reduces the risk of choke and encourages water intake. Prepare soaked feeds just before feeding to prevent them sitting for long periods of time and potentially going bad or becoming less palatable.  

Other Key Considerations for Horses With EOTRH 

Beyond feed amount and frequency, consider water temperature for soaked feeds and your horse’s feed preferences. Very cold water can cause discomfort to animals with dental issues and, because most of these horses are seniors, keep in mind their nutritional needs and feed preferences could change as they age.   

Outside of nutritional management, know your horse’s normal body condition score and recheck it to make sure he isn’t losing condition. Recognize when something is wrong so you can promptly contact your veterinarian. 

Long-term management decisions for horses that have had EOTRH will depend on whether the horse can go back to eating long-stem fiber. When the disease progresses to a point in which the horse can’t consume hay or even chew chopped forages, you might need to switch him to a complete feed that can be fed in many small meals daily. Consult a qualified equine nutritionist if you have questions about optimizing your horse’s nutritional management through dental health challenges.  

Do you have an equine nutrition question?

Breathing properly is a crucial task for a sport horse. If he can’t breathe well, he isn’t going to be successful. All horses working at 60% of their maximum capacity experience hypoxemia—low levels of oxygen in the blood—but those with respiratory disease become even more hypoxemic.

“It’s the way they are built,” says Emmanuelle van Erck-Westergren, DVM, PhD, Dipl. ECEIM, ECVSMR, owner of Equine Sports Medicine Practice, in Waterloo, Belgium. She spoke about respiratory challenges in sport horses at the 2025 IGNITE Sports Science for the Olympic Disciplines Seminar, held Jan. 12-13, in Ocala, Florida.

How Horses Breathe

The horse’s respiratory system differs from those of many other animals. They can only breathe through their nose, so it’s more difficult for them to shift air in and out of their lungs than it is for humans, who can switch to mouth breathing when necessary. They also have a small larynx, and moving a column of air through it consumes energy.

Racing trotters or pacers working at speed take large breaths every few strides, but horses cantering or galloping can’t. They must breathe in and out at the same rate as their strides. This is due to respiratory-locomotor coupling, the synchronized relationship between breathing and stride, where one breath is taken with each stride at a canter and gallop.

How Do Respiratory Issues Affect Sport Horse Performance?

“Horses are massively muscular,” said van Erck-Westergren, making them built to be oxygen deficient. When you lack oxygen, you get tired, she said. The resulting muscle fatigue leads to a decline in performance.

It takes a lot of energy to move oxygen as the horse’s speed increases. The negative pressures applied to the throat can become considerable when the horse canters because no bony structures exist to keep the throat open. The larynx, located at the back of the throat, essentially serves as the dividing mark between the upper and lower respiratory tracts. When the horse is breathing, but not swallowing, there is an open channel into the trachea. After passing through the trachea, inspired air arrives at the bronchial trees within the lungs.

In horses with partial paralysis of the larynx, the more the horse needs air, the more the larynx closes, van Erck-Westergren explained.

Signs of respiratory conditions are not always obvious. There might not be loud breathing noises, cough, or nasal discharge. The only signs could be premature fatigue during exertion or defensive behavior such as exercise intolerance or a reluctance to work. The environment and competitions can challenge horses, making diagnosis tricky, she said. Veterinarians commonly use controlled exercise testing to investigate a problem, observing how a horse recovers. If they suspect a respiratory condition, veterinarians can conduct further diagnostics, including bloodwork and an endoscopy while the horse is at rest or exercising.

Take-Home Message

The horse’s respiratory system naturally operates near its limits, so even a mild breathing problem in a sport horse often results in poor performance. Proper diagnosis and treatment are required for the horse to be able to return to peak form.

Until recently, equine researchers knew little about how dopamine regulates insulin secretion in horses. In two recent studies scientists examined this connection, with implications for managing conditions such as pituitary pars intermedia dysfunction (PPID, formerly called equine Cushing’s disease) and insulin dysregulation (ID).

“A significant number of horses and ponies with PPID produce very large amounts of insulin in response to dietary nonstructural carbohydrates (starches, sugars, and fructans), and this puts them at increased risk of laminitis,” said Simon Bailey, BVMS, PhD, FHEA, Dipl. ECVPT, FRCVS, professor of veterinary biosciences at The University of Melbourne’s Veterinary School, in Victoria, Australia.

Bailey and a research team funded by the Australian Research Council, the Waltham Petcare Science Institute, and Boehringer Ingelheim Vetmedica, including PhD candidate Nicolas Galinelli, have been working to identify the link between PPID and insulin production so they can find ways to better reduce the risk of laminitis in and manage these horses.

Dopamine’s Role in Equine Insulin Response

“Horses and ponies with PPID have reduced dopamine production in the brain (which causes the production of certain hormones from the pituitary gland to get out of control), and we have recently found that it is decreased in the bloodstream as well,” said Bailey.

To investigate the link between dopamine depletion and insulin metabolism in horses, the researchers administered alpha-methyl-para-tyrosine (AMPT), a modified amino acid that inhibits dopamine production, to six healthy Standardbred horses in a placebo-controlled crossover study. Bailey and his colleagues aimed to determine how short-term dopamine reduction affects insulin sensitivity and postprandial (post-meal) insulin responses.

In healthy horses, insulin—a hormone produced by the pancreas—regulates blood sugar by signaling cells to take up glucose and store it as glycogen. In insulin-resistant horses, reduced sensitivity to insulin limits glucose uptake, prompting the pancreas to produce more insulin.

The researchers found that reducing dopamine levels in the horses led to increased postprandial insulin responses. “By temporarily reducing dopamine levels in the brain as well as in the rest of the body, we found that dopamine is not linked to the sensitivity to insulin (in horses, unlike in some other species), but depleting dopamine increases the insulin response to a high-glucose meal,” said Bailey. “Therefore, normal dopamine levels must be helping to keep insulin in check.”

Implications for Treating PPID in Horses

Bailey and his team used the study findings to explore the effects of pergolide—a drug commonly used to treat PPID in horses—on dopamine in horses and ponies with and without PPID. “This drug stimulates the receptors for dopamine, telling the pituitary gland to reduce hormone production, but now we find that it may also affect the pancreas, reducing insulin production,” said Bailey.

However, Bailey added that the drug only partially reduced postprandial insulin response to a high-starch meal, and horses without PPID did not benefit from treatment. “Therefore, in PPID animals or those with equine metabolic syndrome, who are at risk of laminitis due to high insulin levels, they still need to be fed diets low in starch and sugars to avoid excessive insulin levels. Pergolide will not protect them from the effects of high-carbohydrate diets (including lush grass).”

Take-Home Message

Dopamine influences insulin secretion in other species, but its role in equine metabolism has been unclear. Many horses with PPID also experience ID, marked by heightened insulin responses and an increased risk of laminitis. Researchers are still exploring the link between dopamine and insulin production and how this information can be used to more effectively treat horses with metabolic problems. Pergolide had no effect on tissue insulin sensitivity; however, the study results suggest that postprandial hyperinsulinaemia might be limited by this dopamine receptor agonist in animals with PPID and ID. If your horse has metabolic issues, work with your veterinarian to develop an appropriate management and treatment plan.

“We are certainly doing more research in this area to try to better understand these conditions (PPID, EMS, and laminitis) and how they fit together,” said Bailey. “These are such common conditions with huge effects on the well-being of our horses and ponies, so we need to do everything we can in the effort to find new treatments and countermeasures.”

The first study, “Effect of short-term dopamine reduction on insulin sensitivity and post-prandial insulin and glucose responses in Standardbred horses,” was published in Domestic Animal Endocrinology in January 2025. The second study, “Effect of pergolide treatment on insulin dysregulation in horses and ponies with pituitary pars intermedia dysfunction,” was published in Equine Veterinary Journal in February 2025.

Contagious equine metritis (CEM) is a highly contagious venereal disease affecting horses, with potentially severe implications for breeding operations. Caused by the bacterium Taylorella equigenitalis, CEM primarily affects mares, causing vaginal discharge, temporary infertility, and, in some cases, long-term carrier states. Stallions, while asymptomatic, can be silent carriers capable of spreading the disease through natural breeding or artificial insemination.

CEM Transmission and Risks in Horses

Contagious equine metritis spreads in three primary ways:

• Between a mare and stallion during live-cover breeding.
• From stallion to mare via contaminated semen used in artificial insemination.
• From stallion to stallion through shared breeding equipment.

Mares can sometimes clear the infection on their own, but many become chronic carriers, maintaining the bacteria in their reproductive tract and serving as a long-term source of transmission. Stallions, unless diagnosed and treated, can transmit the bacteria indefinitely.

CEM Outbreaks in the U.S.

Although the United States has been considered CEM-free since the mid-1980s, multiple outbreaks have occurred. Six reported incidents have emerged since 2006, with three classified as full-scale outbreaks. The most significant outbreak, spanning 2008 to 2010, involved 23 stallions and five mares. More than 1,000 exposed horses across 48 states were tested, with the infection traced to a stallion imported from a CEM-affected country in 2000.

Between May 2024 and March 2025, the USDA confirmed 52 cases of CEM in an outbreak associated with transmission at a single farm in Florida. The outbreak was first identified when a pony stallion on the farm infected a pony mare that subsequently showed clinical signs of CEM and tested positive for T. equigenitalis. These two animals and one other pony stallion were the only breeding animals involved in the case—the other 49 were geldings who acquired the infection through sheath-cleaning practices on the index farm. None of the geldings arrived at the farm as stallions; current epidemiology (the study of disease, health, and their determinants in populations) indicates one must have arrived infected. In addition to the 52 confirmed cases, officials said at least another 140 were potentially exposed. This is the first finding of extensive gelding-to-gelding spread of T. equigenitalis through inadequate biosecurity during sheath-cleaning practices in the U.S.

Prevention and Biosecurity Measures

To mitigate CEM risks veterinarians recommend the following precautions for breeding operations:

• Adhering to the American Association of Equine Practitioners’ biosecurity guidelines for venereal disease prevention.
• Regularly testing active breeding stallions before the breeding season using direct swab culture for T. equigenitalis. Testing requires collecting swab samples from multiple sites on a stallion’s genitalia and submitting them to a CEM-approved laboratory.

Even a single negative test provides valuable insight into a stallion’s CEM status. However, veterinarians encourage multiple tests to ensure accuracy and prevent undetected carriers from spreading the disease.

To reduce the risk of CEM spread to geldings, experts recommend:

• Wear disposable gloves and change gloves between geldings.
• Use a disposable bucket liner in the wash bucket and paper towels or disposable rags that will not be shared between geldings.
• Avoid using a hose that can become contaminated during handling.

The Stakes for Stallion Owners

The potential financial and horse-health consequences of a CEM outbreak are significant. Beyond the health risks to breeding stock, outbreaks can lead to quarantine measures, disruptions in breeding schedules, increased costs to treat outbreaks, and disruption in the international movement of U.S. horses and semen/embryos.

Ensuring compliance with testing and biosecurity measures is not just about protecting individual breeding programs—it is a collective effort to safeguard the equine industry. Stallion owners, veterinarians, and breeding facility managers play a vital role in preventing future outbreaks and maintaining the country’s CEM-free status.

By taking proactive steps, the equine industry can continue thriving while minimizing the risks associated with this serious but preventable disease.

Editor’s Note: This article has been expert reviewed by Angela Pelzel-McCluskey, DVM, MS, equine epidemiologist at the USDA for accuracy.

Unveiling what EMS and ID really look like

Equine metabolic syndrome (EMS) is not a single disease, say members of the Equine Endocrinology Group in their most up-to-date guidelines¹ and authors of the ECEIM consensus statement.² Rather, EMS is a collection of risk factors for endocrinopathic laminitis—the leading cause of laminitis in horses caused by hyperinsulinemia (elevated circulating insulin levels). The most consistent feature of EMS is insulin dysregulation (ID), which veterinarians can measure relatively easily in horses. Another feature they commonly see in EMS cases is increased generalized or regional adiposity—fat deposits all over the horse or in certain spots.

“EMS results from an interaction between genetic and environmental factors, and the risk of laminitis in the individual animal therefore depends on the cumulative effects of these influences,” states the Equine Endocrinology Group in the guidelines.

This means genetically high-risk horses can develop EMS with only minimal environmental (e.g., dietary) influences, whereas other horses that have a lower genetic risk might develop EMS with improper environments, such as diets high in nonstructural carbohydrates (NSCs).

In this article we’ll describe horses and ponies with a higher genetic risk for EMS followed by some examples of other animals with lower genetic risk for EMS that might still benefit from EMS (ID) testing.

“Recognizing EMS in horses other than the ones we expect, the overconditioned equine population, is important because even nonobese and athletic horses are at risk of career- and life-threatening endocrinopathic laminitis if not recognized and treated,” says Teresa Burns, DVM, PhD, Dipl. ACVIM, an associate professor of equine internal medicine at The Ohio State University, in Columbus.

The True Face of EMS: Obese Ponies

The overconditioned population with regional adiposity at the tail head as well as a “cresty” neck is truly the face of EMS, especially ponies. Current estimates suggest 22-27% of ponies are hyperinsulinemic (Durham et al., 2019).¹

“If there ever were a poster child for anything, overconditioned ponies are it for EMS,” says Burns.

“Ponies come by their EMS risk honestly, it seems,” she adds. “But as we are all increasingly aware, there are many other breeds at elevated risk, including—but definitely not limited to—American Saddlebreds, Morgans, Tennessee Walking Horses, Paso Finos, and Arabians.”

We need to look for not only generalized obesity but also regional adiposity.

“Recent work in certain smaller populations failed to identify body condition score more generally as a risk factor for certain components of EMS (like hyperinsulinemia),” Burns explains. “Instead, regional adiposity of the nuchal ligament (in the neck) and tailhead remains predictive.”

For more specific information Burns recommends referring to studies by Fitzgerald et al., 2019³; Barnabé et al., 2023⁴; and Lykkjen et al., 2023.⁵

“It’s also probably not an accident that when EMS-affected animals lose weight, some of the very last adipose tissue to be mobilized is in those high-risk depots,” she adds. “Lean animals often retain these fat depots, especially members of those high-risk breeds. The biological behavior of this fat appears different (more inflammatory, more insulin-resistant) and, in that respect, yes, it may be more important in the setting of monitoring and managing EMS.”

In a recent study a Nigerian research group (Akinniyi et al., 2023) examined the occurrence of EMS in two separate populations of horses: one group of polo ponies residing in Igabi (60 horses) and a second group of companion horses owned by emirates in Zaria (56 horses). In total, 67.8% of the companion horses were diagnosed with EMS, and the prevalence of EMS in obese horses was 92.86%. Obese horses were more than 10 times more likely to have EMS than underconditioned (a body condition score of less than 4.5 on the Henneke 9-point scale) horses, and horses with a cresty neck were nine times more likely have EMS than horses with normal neck crests.⁶

Breeds ‘Resistant’ to Insulin Dysregulation

“Any horse that is overconditioned to the point of obesity can develop EMS, so no breed is completely immune,” says Burns.

Amanda Adams, PhD, an assistant professor at the University of Kentucky Gluck Equine Research Center agrees, adding, “But even a ‘resistant’ breed, if they are pushed with diet/management in the wrong direction, can become EMS/ID.”

Breeds that seem more “resistant” to ID include Thoroughbreds, Standardbreds, and Quarter Horses, Burns says.

“But we have seen members of virtually all breeds within our hospital population affected, including those listed above as well as draft horses,” she adds. “That said, it’s pretty uncommon to see members of those breeds affected if they aren’t first very overweight. They don’t seem to have the same degree of underlying genetic predisposition as do some of the high-risk breeds.”

So, why are certain breeds more resistant, yet not immune to ID and EMS?

“These more resistant breeds more than likely have a genetic factor that is protective, and we have yet to identify the genes responsible for this protective factor,” says Adams.

“Research is ongoing in this area to unravel these questions, but this is not straightforward,” she adds. “And as we know, even if you identify the ‘protective’ or ‘susceptible’ genes of being ID, there is epigenetics in which diet/environment can turn these genes off/on to be over-/underexpressed, which can then influence phenotype (the observable characteristics) of the animal. This is why diet and management are critical regardless of genetic makeup in how we manage our horses to prevent them from becoming ID/EMS.”

Akinniyi et al. also reported that even nonobese horses have ID/EMS. Specifically, nine of the 16 horses (56%) that were underconditioned and 18 out of 61 (29%) horses with a moderate body condition were diagnosed with EMS. The researchers suggested EMS could be related to internal fat or a genetic predisposition. Or, obesity might not be the primary cause and other as-yet-unidentified underlying causes of EMS could exist.

“It’s not a one-size-fits-all category,” says Adams. “There are multiple phenotypes of EMS, including the lean-type EMS horses, which is why diagnostic testing for ID is so important.”

Equine Athletes Can Be Affected by ID/EMS, Too

Even athletic horses can have ID and should not be ignored simply because they compete and are presumptively extremely healthy. Part of this is because many equine athletes are, in fact, overweight. 

As Burns points out, this is particularly true in certain disciplines.

In a study published in a 2023 edition of the Journal of Equine Veterinary Science, Shannon Pratt-Phillips, MSc, PhD, and her group at North Carolina State University, in Raleigh, highlighted the fact that in elite hunter competition, ponies are often overweight or obese by conventional metrics.⁷

“Judges of conformation and appearance appear to reward this,” notices Burns. “Conformation and hunter disciplines seem to favor individuals with higher body condition scores.”

“These findings show that elite competition ponies are dangerously overweight and that adiposity may influence performance in a judged event,” state Pratt-Phillips et al. in the study. “This is of grave concern to the horse industry and needs to be addressed.”

Horses involved in athletic competition, however, do have one advantage over their sedentary counterparts: Exercise has a beneficial effect on insulin regulation. Because certain ponies, such as Shetlands, aren’t exercised as frequently as equids of other breeds, this could play a role in why ponies are at a higher risk of developing EMS/ID.¹

In the Nigerian study Akinniyi reported that 67% of the leisure horses rarely exercised had EMS. However, 20% of the polo ponies that were exercised were still diagnosed with EMS.

Eyeing ‘Healthy’ Horses for Early EMS Signs

While obesity, regional adiposity, and cresty necks certainly tip our radar in the direction of EMS, prompting diagnostics, the at-risk breeds can be affected even while lean and young, says Burns.

Adams notes that “early” signs of EMS/ID are not always easy for people to see, leading owners to believe their horses are healthy.

“Early signs of EMS, such as cresty neck and regional adiposity, including fatty accumulation over the shoulders, ribs, above the eyes, and the rump, can be easily missed by owners if they see the horse daily,” she says. “This is why it’s important to consider ID testing as part of a yearly veterinary examination as a preventative measure.”

This will allow veterinarians to give unbiased evaluation of the animal.

“It’s always better to do the testing rather than guessing,” Adams says.

Horses With Concurrent PPID

If a horse has pituitary pars intermedia dysfunction (PPID, aka equine Cushing’s disease), it’s always a good idea to also test for ID in horses showing clinical signs, says Adams.

Burns adds, “About 30-40% of horses with PPID also have ID.”

But PPID doesn’t necessarily need to be considered in all horses with ID.

“Testing for ID may happen when an animal is on the younger spectrum of age scale, and we know that PPID is more prevalent in older horses,” Adams notes. “I also think testing for both conditions when the horse starts to reach about 15 years of age is a good idea.”

Burns agrees, adding, “As testing strategies for both conditions are refined over time, the prospect of screening populations at risk before any clinical signs of disease are present (and intervening appropriately) is becoming more feasible.”

While researchers are still developing concrete recommendations, Burns says many equine veterinary practices are already adding screening tests to their wellness plans for certain demographics, such as annual measurement of endogenous adrenocorticotropic hormone (ACTH, a hormone that’s elevated in horses with PPID, measured at rest) concentration in the fall for individuals over 15 years of age and annual oral sugar testing in the spring for individuals of breeds predisposed to EMS over 4 or 5 years old.

“Again, such screening protocols for either condition in asymptomatic patients haven’t been validated or formally endorsed, but that capability is a shared goal of several research groups that are active in the field currently,” she adds.

After the Unveiling: Control Hyperinsulinemia

After veterinarians diagnose EMS/ID (see TheHorse.com/1116972), their main treatment goal is to rapidly decrease circulating insulin levels to prevent/quickly resolve laminitis. The Equine Endocrinology Group’s first line of attack on EMS is diet. If you own an animal with EMS, restrict his grazing to little or no grass and stop providing treats and grain (concentrate feed). Here are some other recommendations: Feed to achieve or maintain a body condition score of 5, offering only grass hay low in NSC. (Have the hay tested for NSC content and/or soak the hay to reduce NSCs.) Be certain to offer a low-intake ration balancer with a low sugar content (soaking can leach nutrients from the hay). If laminitis does not preclude exercise, incorporate an exercise program into the horse’s routine. Researchers say even low-intensity exercise involving 30 minutes of unridden fast trot or canter to achieve heart rates of 130-150 beats per minute three times weekly is likely beneficial for these horses.

“It’s important to feed less than 12% NSC hay,” adds Adams. “This is the current guideline; however, my research group is working very hard to put science behind this recommendation. This will better help determine what the ‘safest’ percent NSC in hay is to reduce insulin responses postprandially (after a meal).”

For more information refer to Macon et al., 2022 and 2023.^8-10

Adams also points out that owners not only need to feed low-NSC hay but also restrict the amount of hay they offer to 1.5% of the horse’s body weight per day.

For animals not responding to diet and exercise or in cases of severe laminitis, practitioners might need to rapidly correct ID using medications such as metformin, levothyroxine, and the sodium-glucose cotransporter 2 (SGLT2) inhibitors. These medications are not labeled for horses and must be used under the direct supervision of a veterinarian.

Take-Home Message

Adiposity is a key clinical feature of EMS. Given a preponderance of ponies and horses are overweight, veterinarians and horse owners should consider EMS in many of those animals, particularly if they are at-risk breeds. Still, do not discount EMS in breeds at lower risk, athletic horses, and even other apparently healthy horses. “We should now be actively looking outside of the ‘fluffy’ pony paradigm for equids at risk for EMS,” says Burns. “It can truly affect any of them.”

References:

1. Frank N, Bailey S, Bertin F-R, et al. Recommendations for the diagnosis and management of equine metabolic syndrome. 2022. tinyurl.com/cz2wy8kt

2. Durham AE, Frank N, McGowan CM. ECEIM consensus statement on equine metabolic syndrome. J Vet Intern Med 2019;33(2):335–349.

3. Fitzgerald DM, Anderson ST, Sillence MN, de Laat MA. The cresty neck score is an independent predictor of insulin dysregulation in ponies. PLoS ONE 2019;14(7):e0220203.

4. Barnabé MA, Elliott J, Harris PA, Menzies-Gow NJ. Relationships between total adiponectin concentrations and obesity in native-breed ponies in England. Equine Vet J. 2023. In Press.

5. Lykkjen S, Stenbakk LK, Holmøy IH. Prevalence and risk factors for laminitis within the Norwegian pony breed Nordlandshest/Lyngshest. Acta Vet Scand. 2023;65:22.

6. Akinniyi OO, Sackey AKB, Ochube GE, et al. Occurrence of equine metabolic syndrome, clinical manifestations, and associated risk factors in Nigeria. J Equine Sci 2023;34(2):29–35.

7. Pratt-Phillips S, Munjizun A, Janicki K. Visual assessment of adiposity in elite hunter ponies. J Equine Vet Sci. 2023;121:104199.

8. Macon EL, Harris P, McClendon M, Perron B, Adams A. Insulin dysregulated horses metabolic responses to forage pellets. J Equine Vet Sci. 2023;133:104991.

9. Macon EL, Harris P, Bailey S, Caldwell Barker A, Adams A. Identifying possible thresholds for nonstructural carbohydrates in the insulin dysregulated horse. Equine Vet J. 2023;55(6):1069–1077.

10. Macon EL, Harris P, Bailey S, Barker VD, Adams A. Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared with non-insulin dysregulated controls. Equine Vet J. 2022;54: 574–583.

Metabolic disorders are becoming more common in horses and, without proper care, can lead to endocrinopathic laminitis. Managing these conditions effectively can be challenging. For horse owners, understanding insulin dysregulation (ID) and implementing effective prevention and management strategies is critical for the long-term health of horses with ID.

What is Insulin Dysregulation in Horses?

Insulin dysregulation compromises the horse’s ability to metabolize soluble carbohydrates. The broad term that encompasses both tissue insulin resistance and elevated blood insulin (hyperinsulinemia). “Not all horses exhibit both conditions, though; some only have insulin resistance, while others may have elevated insulin levels after eating,” says Erica Macon, MS, PAS, PhD, an assistant professor at Texas A&M University, in College Station. “Either condition is a cause for concern in the development of endocrinopathic laminitis.”

When a healthy horse eats nonstructural carbohydrates (NSC, starch and sugar) the digestive enzymes in the gastrointestinal tract break them down into glucose. When blood glucose levels rise, the pancreas releases insulin, which helps the glucose move from the blood into tissues. This then reduces blood glucose levels, and the pancreas reduces insulin secretion in response.

“These horses tend to have some degree of insulin resistance, where insulin fails to do its normal job after a meal rich in NSCs of helping the absorbed glucose to get from the blood and into tissues like the muscle, to reduce blood glucose concentrations back to normal,” says Shannon Pratt-Phillips, MS, PhD, PAS, a professor in the Department of Animal Science at North Carolina State University, in Raleigh. “In these horses the pancreas releases very high amounts of insulin to try to deal with the glucose load and its (insulin’s) reduced effectiveness, but glucose concentrations fail to come back to normal as quickly as healthy horses. Horses with ID tend to also have elevated insulin concentrations even without a previous meal.”

Hyperinsulinemia has been shown to cause laminitis, a painful condition characterized by inflammation of the laminae (the tissue that connects the hoof wall to the underlying coffin bone) that potentially leads to separation and rotation of the coffin bone. In these cases it’s referred to as endocrinopathic laminitis.

Which Horses Are at Risk for ID?

Multiple risk factors can contribute to an equid developing ID. “There is both a genetic and environmental component,” says Macon. “Have you ever been asked during a doctor’s appointment if diabetes runs in your family? Equids experience a similar genetic predisposition to ID and obesity. For some equids their genetics simply aren’t in their favor. For example, Spanish breeds and most pony breeds are more prone to being overweight and developing ID.”

Horses with pituitary pars intermedia dysfunction (PPID, formerly equine Cushing’s disease) are more likely to develop ID. Researchers are still working to fully understand this connection, says Macon.

Although obesity and disorders such as PPID are primary risk factors, horses that do not match that description can also have metabolic problems. “It is possible for a horse to be ID and be lean, or an obese horse to have normal glucose and insulin responses to a simple carbohydrate meal,” says Pratt-Phillips. “Horses that are fed high amounts of NSCs on a regular basis may also have lower insulin sensitivity.”

Even if your horse does not match the usual “at-risk” description, it is important for him to maintain a healthy body condition to reduce his risk of developing metabolic problems. Your horse should not exceed a body condition of 6 on the Henneke nine-point system. “You should always be able to feel a horse’s ribs,” says Pratt-Phillips.

Feeding Horses With ID

If your veterinarian diagnoses your horse with ID, consider a few key aspects of his management. If the animal is obese, work with an equine nutritionist to adjust his diet for weight loss. However, if he has been diagnosed with PPID, work closely with your veterinarian to medically manage him as well.

Regardless of the underlying cause, horses with ID should eat a diet low in NSCs, which you can calculate based on the feed label. “I use NSC (water-soluble carbohydrates plus starch) because it includes fructans,” says Macon. “Now, not every horse responds to fructans, but some horses do, so I like to err on the side of caution.”

The percentage of NSCs in the diet is often a driving factor for horse owners in determining if a forage or concentrate is going to be safe for their ID horse, but the industry is moving away from relying on a percentage.

“When we think about a percentage, we don’t take into consideration where that starch is coming from or how bioavailable it is, so breaking down the actual load on a grams per kilogram body weight (BW) seems to be the better option,” says Macon. “Up until my work, there wasn’t any NSC threshold studies done in metabolic horses.” Researchers have now found 0.1 grams of NSC per kilogram of body weight per meal to be the safe threshold for metabolic horses.

Therefore, when designing your horse’s feeding plan, find the percentage of NSC in the feed, the amount of that feed your horse receives at each meal, and your horse’s body weight. Use the below calculation to ensure you do not exceed 0.1 g NSC per kg BW per meal.

Calculating NSCs in Your Horse’s Meal

Information Needed

1. Horse’s ideal BW
2. NSC % of commercial grain
3. Feeding rate for horse’s ideal BW based on manufacturer’s instructions

Calculation

1. Convert horse’s weight to kilograms.
2. Convert total feeding rate to grams.
3. Ensure NSC % is on a dry matter basis. Pelleted concentrates are 95% dry matter. Textured concentrates are 90% dry matter.
4. Multiply the NSC on a dry matter basis and the feeding rate in kilograms.
5. Divide the grams of NSC in the concentrate by the animal’s BW in kilograms.

Example Calculation

Horse’s body weight = 500 kg

Feeding rate of concentrate = 1,800 g

NSC % = 12% on a dry matter basis

(0.12 NSC dry matter basis) x (1,800 g) = 216 g NSC in the concentrate fed daily

216 g NSC / 500 kg = 0.43 g NSC provided in the concentrate daily

“If your horse’s meal is too high in NSCs, you can split the feeding into more meals per day so that each one is smaller and will have less glucose,” says Pratt-Phillips.

When choosing your horse’s forage, consider both the NSC content of the hay and the time the horse takes to consume it after each feeding. While less research exists in this area, the current recommendation involves providing low-NSC hay (below 10% on a dry matter basis) and encourages prolonged feeding time. “Implementing slow-feeding strategies to make sure that the horse is having a smaller quantity over a longer period of time I think is the safest bet that we can go with right now versus throwing two flakes on the ground and letting them consume it rapidly,” says Macon.

Take-Home Message

Our scientific understanding of equine metabolic problems constantly expands. Understanding ID and which horses are at risk will help you recognize issues with your horse’s metabolic health and seek veterinary intervention. Prevention is also important, keeping horses lean and avoiding obesity to reduce their risk of developing ID. New calculations for determining the NSC content of your horse’s meals can help you accurately determine if his diet is safe for his metabolic health.

Q: My easy-keeper horse had laminitis a few years ago, and ever since then I have controlled his hay intake to ensure he maintains an adequate body condition score. My concern is his hay ration does not last him 24 hours, even with a hay net. I have heard that horses should not go without hay, therefore I am wondering what management tactics could help his hay last longer? And should I be concerned when his hay runs out?

A: It is great to hear your horse has maintained a healthy body condition (which should be 4-5 on the Henneke scale) after recovering from laminitis. As you know, it can be very challenging to manage these easy keepers.

You are correct in that it is important to ensure that horses do not have extended periods of time without access to hay. However, for horses that tend to be overweight, they are typically unable to have free-choice hay because this can result in obesity, which is a serious health concern. 

The Importance of ‘Trickle Feeding’ for Horses

The reason horses need access to hay or roughage for most of their time stems from how they have adapted to eat. Horses are trickle feeders and graze for upward of 18 hours per day. Therefore, their anatomy is designed to support trickle-feeding behavior. For example, unlike in humans, when horses chew, it stimulates salivation. Saliva is important for both moistening feed and as a gastric buffer, so it’s crucial to consider chew time when determining how to feed your horse his hay rations.

Additionally, the stomach continually produces gastric acid—even when the horse is not eating. Lack of forage in the horse’s stomach creates a much more acidic environment and can increase the risk of gastric ulcers developing.

There are many anatomical reasons to support trickle feeding, but it is important to keep in mind that obesity is also a serious health issue in horses. It is not always as simple as hanging a hay net and hoping our easy keepers can pace themselves.

How Much Hay to Feed an Easy Keeper

When restricting forage, you must still meet the minimum hay intake of 1.5% of the horse’s body weight daily. For example, a 1,100-lb horse needs to consume a minimum of 16.5 lbs of hay daily. Be sure you are implementing slow-feeding methods, such as hay nets, and offering multiple feedings so the horse is never without hay for longer than four hours.

If you have an easy keeper and he runs out of hay an hour or two before his next feeding, it is not a cause for concern if he seems content otherwise. However, if he is having any prolonged periods (three to four-plus hours) without hay then you might need to consider management changes such as feeding him more often. Additionally, if the horse is displaying unwanted behaviors—for example, wood chewing—during the hour or two he is out of hay, this is a sign that you might need to adjust your feeding schedule. In situations when labor is not easily available, there are a few different automatic feeders on the market that could be used as well.

Hay Quality for Horses With Metabolic Issues

A commonly overlooked aspect of feeding easy keepers is evaluating the energy content of the hay—that is, the calories it offers. If your easy keeper is running out of hay too quickly, testing it to evaluate the energy content should be the first step. Easy keepers should eat Grade 3 or 4 “utility hay” based on the American Forage and Grassland Council grade scale. This is hay that is lower in digestible energy, with acid detergent fiber (ADF) content of 41-45% and neutral detergent fiber (NDF) content of 54-65% on a dry-matter basis.

When we match the quality of the hay to our horse’s needs, it can make the management much easier. For example, with your easy keeper, if you source lower-energy hay, it might mean he can consume more without gaining excess weight, so his daily hay ration could last longer.

Straw as an Additive for Easy Keepers

Another management tactic for these horses is to incorporate some straw into their ration. Straw is the byproduct of cereal crops (what is left over after the grain is harvested). Horse owners can use it for easy keepers because it is low in nutritional value and, therefore, low in energy. Please note that due to straw’s low nutritional value, you should not offer it as the primary forage for a horse, but it can make up to 25% of their forage.

As with any diet change, introduce straw over a minimum of seven days so that the horse can gradually adjust and to reduce the risk of gastrointestinal upset. Another key consideration you should make for any horse, but especially those consuming larger amounts of indigestible fiber, is water intake. Be sure your horse is receiving adequate salt and has free-choice access to a fresh and clean water source.

The goal of either sourcing lower-energy hay or incorporating some straw into the ration is to increase the amount of roughage the horse can consume, which helps prevent any fasting periods and increases chew time without significantly increasing digestible energy intake. Test both your hay and straw prior to feeding it to your horse to be sure it is safe for them. If you are unsure of the safety of a forage source, consult a qualified equine nutritionist prior to feeding it.

Even with lower-energy forage, and incorporating straw, slow-feeding tactics are often still necessary. If you are using a hay net, and your horse is continuing to eat too quickly, you could reduce the hole size of the net, or even double-net the hay to slow him down.

Slow-Feeding Tactics

Anytime you implement a new slow-feeding tactic, for example, double-netting, observe your horses to ensure they can consume the hay. Occasionally, if it is too difficult for them, they could become frustrated and give up on trying entirely.

Each horse is truly an individual, so you might have to experiment with a few different types of hay nets or slow feeders prior to finding one that works best for your horse. As horses get used to eating from hay nets, they become more skilled with it, and you might be able to gradually work them to nets with smaller holes or double-netting. Slowing down their intake is important, of course, but also consider any ways in which you can increase your easy keeper’s movement. You can use hay balls or play around with the paddock setup. For example, using multiple smaller hay nets so horses must travel between them or even setting up a track system are great options to encourage natural movement.

Take-Home Message

Overall, carefully managing easy-keeping horses and those at risk of obesity is imperative for their health. However, it can be challenging to provide them with adequate roughage while ensuring they do not become overweight. So, if your horse is on a good slow-feeding program and you have tested your hay, rest assured that your horse will be fine if he runs out for an hour here and there. However, if he experiences prolonged fasting periods, investigate the various management tactics you can use to reduce his time spent without forage.

Do you have an equine nutrition question?

Recent discussions on social media have raised concerns regarding the identification of Jamestown Canyon virus (JCV) in a Pennsylvania horse. What do we know about this virus, and what is there to be discovered?

What We Know About Jamestown Canyon Virus in Horses

Jamestown Canyon virus is a mosquito-borne virus that primarily affects humans. Researchers first identified this virus in Colorado in 1961. It is spread by mosquitoes that pick up the virus when feeding on infected animals, especially deer; mosquitoes then transmit the virus to other animals, including humans. Most animals and people exposed to JCV do not appear sick, although there have been rare cases of severe neurologic (brain and spinal cord) disease associated with JCV in people.

Jamestown Canyon Virus Infection in Horses

Jamestown Canyon virus is not a new virus and should not be a cause for alarm for horse owners.

In seroprevalence studies researchers look for antibodies against a particular pathogen (a disease-causing organism such as a virus or bacterium); in North America they have revealed horses have likely been exposed to JCV for decades, with studies as far back as the 1970s showing a subset of horses has been exposed. There are very rare reports of the virus causing illness in horses. The only known published report of JCV infection in a horse involved blisters affecting the coronary band and mouth of a Colorado horse in 1997.

More recently, scientists identified the virus in spinal fluid samples from a horse seen at the University of Pennsylvania’s New Bolton Center, in Kennett Square, in late October 2024. The patient was euthanized due to significant neurologic disease and, after extensive testing efforts over several months, clinicians identified JCV in that horse’s samples.

This is the first case we are aware of where this virus was identified in a horse with neurologic disease. Given what we know about exposure of horses to the virus and how rarely we see disease associated with JCV in horses, this is unlikely to be a significant cause of disease in horses. However, in response to this novel detection, researchers at Penn Vet are working with other University of Pennsylvania researchers to better understand how JCV affects horses. If you are interested in donating to support this research, please visit this link.

What Can Owners Do To Protect Their Horses?

To protect yourself and your horse from JCV, do what you can to reduce mosquito populations near your barns by eliminating standing water and take steps to prevent mosquito bites. For more information about JCV in people, mosquito-bite prevention, and Pennsylvania surveillance for mosquito-borne disease, please see the Pennsylvania Dept of Health JCV Fact Sheet and the Pennsylvania Department of Environmental Protection’s mosquito map.

Q. My horse is starting to shed his winter coat, and I’m wondering whether there is anything I can do nutritionally to speed up the process and that will also ensure a good-quality summer coat?

A. While most of us look forward to the longer days and warmer weather of spring, shedding horses can leave the barn looking like a yak thanks to shedding winter coats. I don’t blame you for wanting it over as quickly as possible!

Some anecdotal reports suggest that feeding flax or black oil sunflower seeds can help horses shed out more quickly. This is likely due to the oil these feeds contain. However, I have found no scientific evidence to support this assertion. The best way to speed up the removal of old coat is rigorous grooming before and after exercise using a rubber curry comb or similar grooming tool. If the weather is warm enough, a bath will often help loosen hair. So will a good roll in a sandy arena.

Don’t be fooled into thinking that blanketing your horse will help them shed faster. Day length is what triggers hair loss, not body temperature.

Fat and Horse Hair Coat Quality

While feeding fat to speed up shedding might be no more than placebo effect, adding more fat to the diet might help improve the new coat’s quality. The hair shaft is coated in cuticle cells that contain a substantial amount of fat that helps retain moisture. These cells should lay flat, and when they’re flat they reflect light beautifully. However, if damaged, moisture is lost from the hair shaft, and the hair becomes dry and no longer reflects light with the same brilliance. Additionally, pores in the skin release sebum, which is an oily substance that coats the hair shaft and helps maintain shine. Diets that don’t provide adequate amounts of fatty acids could result in a dry hair coat that’s more susceptible to damage and a dull appearance.

Take caution before supplementing fat to ensure it is appropriate for the individual horse based on body condition. However, even relatively small amounts of fat should have a positive impact on coat quality. Try to use fat sources that provide essential omega fatty acids especially those that supply greater quantities of omega-3 than omega-6. Flax and camelina oil are good options, and you only need to feed about 2 to 4 ounces per day for an average-sized horse. If feeding flax seed, either whole or ground, feed about 4 to 6 ounces by weight, which is about 1 cup by volume.

Supplementing oil also supports supple, healthy skin and reduces dandruff and flakiness.

Vitamins

Vitamin A is a key nutrient that plays a role in skin health, and while the equine dietary deficiencies are rare, they can occur if you’re feeding older hay. While the precursor to vitamin A, beta-carotene, is abundant in fresh forages, it is lost from hay at a rate of almost 10% per month. Therefore, by late winter/early spring hay might have lost 50% of its beta-carotene, and by the time hay is a year old it’s likely horses will need an additional vitamin A source to meet their basic dietary requirements.

Protein and Amino Acids

The hair shaft is made up mostly of the protein keratin. Diets that provide inadequate protein or that lack essential amino acids could result in reduced hair growth. This, in turn, could slow down shedding. Look at the quality of the forage you’re feeding. Very stemmy hay, the result of cutting plants when they are mature, might need to be supplemented with feeds that provide quality protein, such as soybean meal.

Copper and Zinc’s Role

Ensuring horses’ dietary copper and zinc requirements are met will also help support coat color. Both these minerals impact melanin, the protein in hair that is responsible for pigmentation. If the hair contains inadequate amounts of melanin, it is unable to resist damage from ultraviolet light. This leads to oxidative damage and fading.
Copper is also needed by the enzyme lysyl oxidase, which is necessary for the maintenance of the cross-bridges in collagen within skin. Without adequate copper these cross linkages are weakened and the skin loses structural integrity.

Take-Home Message

A balanced diet with appropriate levels of protein, trace minerals, and vitamins supports healthy skin and coat. For greatest effect you should make sure that all dietary requirements are met before shedding starts. That way the new coat will be fully supported from the very beginning of its growth. Combine this with rigorous grooming sessions and you will have a fabulous summer coat before you know it.

Q: I’ve always heard horses are more prone to impaction colic during winter, especially if they don’t drink enough water. Is this true? If so, what can I do to reduce my horse’s risk of impaction colic this winter?

A: At its most basic, colic is a term covering a wide variety of abdominal pain and can occur throughout the year. Impaction colic describes an incidence of colic related to a large bolus of feedstuffs or waste being caught (impacted) within the intestines. Impaction colic during the colder months is commonly associated with two dietary changes: an increase in the amount of dry feed consumed (especially hay) and a decrease in water intake.

A quick way to determine if your horse is consuming enough water is to routinely monitor his feces. If you notice dry, hard, and crumbly fecal balls, he is not drinking enough.

What Horses Are Prone to Impaction Colic During Winter?

Not all horses develop impaction colic during winter. Owners and managers can decrease their horses’ potential for the condition by monitoring diets, especially forage quality, water intake, and making sure fresh water is always available.

Horses evolved as animals that spend a significant amount of their time walking around and consuming forage. This almost constant movement helps keep the digestive tract moving feedstuffs and waste through, so we should make sure our horses get exercise. When storms or weather extremes arrive, we often believe putting our horses in stalls is in their best interest. However, researchers have shown equine gut motility significantly decreases the first few days after a horse moves inside for stall confinement, which can lead to an increase in impaction colic risk.

Improving Water Intake to Reduced Risk of Impaction Colic

The average adult horse consumes approximately 1 gallon of water per 100 pounds of body weight, or approximately 10 gallons if he’s a 1,000-pound horse. Horses need water for proper digestion and movement of feedstuffs through the digestive tract; the drier the feed provided, the more water the horse needs for the digestive tract to function properly.

In colder months, be certain your horse has water available that is not frozen. Some horses are willing to break a layer of ice if it forms on top of the water source, while others are more reluctant. Check your horse’s water sources several times each day to ensure they have not frozen. If your horse doesn’t want to drink very cold water, consider adding warm water (even from a thermos if you don’t have hot water in your barn) to bring up the water temperature in his buckets. You can also find ways to insulate buckets to help keep water from freezing if you cannot use heated buckets or trough heaters.

Top dressing either concentrate or flakes of hay with some loose table salt or other electrolytes can encourage a horse to drink. Soaking his feed and making a mash or slurry also incorporates more water into his diet. Although horse owners have historically used bran mashes, suddenly providing a feed like this can cause digestive upset or unbalance the diet. Now researchers discourage owners from feeding a true bran mash.

Take-Home Message

Keeping your horse hydrated is a key step to limiting his risk of impaction colic. Make sure the water you provide him is palatable and not frozen and be sure he has exercise opportunities to improve gut motility. Finally, check his hydration status daily to ensure he consumes enough water.

Do you have an equine nutrition question?

Equine asthma can affect horses of any age, breed, or discipline, making it harder for them to breathe properly and limiting their performance. The FDA has approved treatments such as inhaled ciclesonide for treating severe equine asthma, but these drugs’ efficacy in moderate cases is less clear.

Macarena Sanz, DVM, PhD, Dipl. ACVIM-LA, now an associate professor of equine medicine at Iowa State University, in Ames, along with her collaborators examined the potential benefits of inhaled ciclesonide for moderate equine asthma. The study, conducted while Sanz was at Washington State University (WSU), in Pullman, involved researchers from WSU, other Washington clinicians, and the University of Calgary, in Canada. Sanz and the team shared their findings in the Proceedings for the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida.

Studying Ciclesonide in Horses With Asthma

Sanz and the research team studied 21 young racehorses confirmed to have moderate asthma over 10 days. They split the horses into two groups—one treated via an inhaler system with ciclesonide (12 horses) and a placebo group that use the inhaler without ciclesonide (9 horses). They blinded the researchers, trainers, owners, and grooms to the treatments.

The researchers performed a tracheal endoscopy on Day 0 and Day 10 and scored the  mucous present, bronchoalveolar lavage (BALF) cytology (looking at the cells under a microscope), and polymerase chain reaction (PCR) testing of BALF cell cytokines (cell-signaling proteins). They also asked the owners, trainers, and grooms to assess and score the horses’ respiratory signs daily.

In the horses treated with ciclesonide, the researchers noted improvement in the percentage of inflammatory cells and cytokines in the BAL F on Day 10. The owners, trainers, and grooms also noted a daily improvement in these horses’ clinical signs. “The treatment improved clinical signs, cough in particular, and decreased the percentage of mast cells in their bronchoalveolar lavage fluid, consistent with less inflammation,” said Sanz.

Clinical Applications and Future Ciclesonide Research

“We showed that treatment with inhaled ciclesonide can benefit young racehorses with moderate asthma,” said Sanz. Based on the team’s findings and because the inhaler system used in the study has been discontinued, Sanz said she and her fellow researchers believe veterinarians and researchers should evaluate the efficacy of ciclesonide administered through other available nebulizer systems.

“We showed a positive effect in young racehorses, but our study did not evaluate the duration of this response after the treatment discontinued,” said Sanz. She suggested following these horses for a longer period of time in future studies to evaluate the long-term efficacy of the drug.

Equine herpesvirus-1 (EHV-1), a significant cause of respiratory and neurological disease in horses, can spread stealthily at equestrian events, often going unnoticed. Nicola Pusterla, DVM, PhD, Dipl. ACVIM, AVDC-Equine, professor of equine internal medicine and epidemiology at the University of California, Davis, School of Veterinary Medicine, recently led research on the role that subclinical shedders—those that do not show signs of infection—play in spreading the virus. He presented his findings at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida, and raised concerns about current practices for detecting and managing EHV-1.

Silent Shedding and EHV-1 Environmental Spread

Horses that appear clinically healthy might still shed EHV-1 and contribute to outbreaks, complicating efforts to prevent viral spread. Pusterla’s research team tested 162 apparently healthy horses at a California horse show in April 2022. While only three (1.85%) horses tested positive for EHV-1 using quantitative PCR (qPCR), testing environmental samples from stalls revealed more positive results.

Immediately after the event the researchers collected sponges (specifically used to collect samples) from stalls and identified, among others, five EHV-1-positive stalls in one barn. “This clustering pattern confirms that the respiratory virus can easily spread among horses sharing close quarters and suggests that transmission might occur more subtly than we previously understood,” Pusterla said.

Focusing on EHV-1 Environmental Detection

The research team conducted a second study to evaluate the accuracy of environmental sampling in detecting EHV-1. They collected samples daily for 11 days using nasal swabs, stall sponges, air samples, and stall strips in an eight-stall barn housing seven adult horses aged 5 to 16 years old. Four horses had been vaccinated with a modified-live intranasal EHV-1 vaccine to mimic subclinical shedding; the remaining three horses were unvaccinated.

All intranasally vaccinated horses shed EHV-1 in nasal secretions at levels and for a duration similar to what is expected in subclinical shedders, while none of the controls had detectable EHV-1 in nasal secretions (the EHV-1 vaccine strain is harmless and cannot be transmitted to other horses, hence it does not contribute to the spread of EHV-1). The team used sponges to detect EHV-1 in the stalls of all vaccinated and one control horse. With stationary strips they detected EHV-1 in the stalls of three of four vaccinated horses but none of the controls. Air samples showed low detection rates, likely due to low concentrations of aerosolized EHV-1.

“The highest detection rates came from stall sponges, particularly in feeding areas where droplet contamination from nasal secretions is likely,” Pusterla said. The researchers established that the virus did not necessarily transfer directly between horses but did accumulate in shared and high-traffic spaces such as stall walls and water buckets.

Implications for Biosecurity at Equine Events

Pusterla’s research highlights the importance of implementing biosecurity measures to control EHV-1 at horse shows. He reported that traditional diagnostic methods, such as nasal swabs, are invasive and might miss shedding. Environmental sampling, particularly with stall sponges, could offer a more effective and practical approach to identifying viral clusters and taking preventive measures. However, the study’s limitations include a small sample size and no assessment of viral viability in the environment.

Take-Home Message

Pusterla emphasized the need for vigilant monitoring and proactive strategies to mitigate EHV-1 risks. Farm owners and managers should prioritize good biosecurity practices with their hygiene and cleaning efforts, especially in areas prone to droplet contamination, such as feeding zones and high-traffic areas. Equally important, environmental testing could be a vital tool for early detection and prevention of outbreaks, helping limit the silent spread of EHV-1.

Working donkeys in Kenya need upper airway evaluations, yet equipment and hygiene limitations can make this task challenging. Anya Floyd, DVM, BSc, of Energy Equine Veterinary Services, in Alberta, Canada, described how to use a borescope double wrapped with sanitary sheaths to easily perform this task in less-than-ideal field conditions. Upper airway borescope examinations might help improve the welfare and working conditions of these animals.

“Donkeys are extremely hard-working animals,” said Floyd during her presentation at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida. “Their primary duty is pulling very heavy carts, and these carts and the harness system are rudimentary, tied directly to the neck below the jaw using feed sacks, rope, old pants … anything owner can find. Not surprisingly, this harness system can negatively affect the respiratory system, impacting welfare.”  

Uing an Accessible Borescope for Upper Airway Endoscopy in Donkeys

Recognizing the importance of examining the respiratory tracts of these animals, Floyd and her supervisor Martha Mellish, DVM, Dipl. ACT, of the Department of Health Management at Atlantic Veterinary College, in Prince Edward Island, Canada, purchased a simple 1.5-meter flexible borescope capable of capturing videos and images. The major concerns were:

1. Keeping the scope clean as it passed through the upper airways
2. Cross contamination when there was no reliable access to clean water, only alcohol towelettes

Floyd and her team used two disposable artificial insemination (AI) sanitary sleeves to double-wrap the borescope. Specifically, they cut one sleeve below the perforation, creating an opening at both ends of the sleeve. They fixed this open end was fixed to the camera (at the tip of the borescope) using electrical tape. The second AI sanitary sleeve had a sealed end, which they placed over the camera end to protect it while it was passed through the upper respiratory passages.

“Once the borescope was advanced through the ventral meatus (the widest and shortest nasal passage), the camera was advanced through the outer AI sleeve, revealing a completely clean scope and lens, ready to go,” said Floyd.

None of the donkeys were halter broke, so the veterinarians needed to apply chemical restraint and a nose twitch for the procedure.

Testing the Diagnostic Capabilities of the Borescope

Floyd performed 80 scopes in the field using this technique. She considered the scopes diagnostic if she could view the arytenoid cartilage, vocal folds, epiglottis, and trachea to a depth of 40 centimeters to 60 cm from nares (nostrils).

Unlike horses, “donkeys have narrow nasal passages compared to their head sizes, have fleshy and bulbous arytenoids, and the epiglottis is pointed,” said Floyd.

Lubricating the borescope to facilitate its passage helped limit trauma and hemorrhage during the procedure. Elevating the head made passing the scope easier as well.  

One inherent limitation the veterinarians discovered was the borescope’s excessive flexibility. It sometimes got kinked in an “S” shape the team couldn’t correct, so they had to withdraw the scope and reset it.

Take-Home Message

Performing upper airway endoscopy exams in working donkeys is important for their overall health and welfare; however, traditional endoscopes are not always available in some regions. Therefore, borescopes, which can be more easily purchased, might be a useful alternative when endoscopes are unavailable. “The borescope does not fully replace a traditional endoscope but can provide diagnostic data for respiratory health in donkeys,” said Floyd.

Mean glandular severity scores were significantly lower in the treatment group on Days 28 (shown) and 35, as seen on gastroscopy exam. | Courtesy Dr. Frank Andrews

Equine gastric ulcer syndrome (EGUS) refers to any ulceration inside a horse’s stomach. It often causes severe physical pain, leading to clinical signs such as behavior changes, weight loss, and loss of appetite.

Veterinarians view omeprazole as the mainstay EGUS treatment, said Frank Andrews, DVM, MS, Dipl. ACVIM, LVMA equine committee professor of equine medicine and director of equine health and sports performance at Louisiana State University’s School of Veterinary Medicine, in Baton Rouge. He spoke on the subject at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida. But because omeprazole might not be suited for long-term use, he said he and his team studied a schizophyllan—a beta-glucan—and hyaluronan product (relyneGI) to see if it could be useful in caring for ulcery horses.

Schizophyllan and Hyaluronan

Hyaluronan is a high-molecular-weight glycosaminoglycan in joint, intestinal, and gastric tissues. “It functions to maintain gastric and intestinal homeostasis, innate immunity, and modulates inflammation,” said Andrews. “In rats—which have a similar stomach to a horse with a squamous and glandular region—hyaluronan has been proven to protect the gastric lining and improve gastric mucosa integrity.”

Beta-glucans are an integral part of cell walls; schizophyllan activates immune cell maturation, differentiation, and proliferation. They have prebiotic properties and have been proven safe for use in horses.

Andrews and his team studied the efficacy of the new schizophyllan and hyaluronan gastric support supplement in 12 stall-confined Thoroughbred and Thoroughbred-cross horses with naturally occurring gastric ulcers. They divided horses evenly into treatment and control groups, performed gastroscopic exams, and weighed each horse at the start of the study after two days of acclimatization.

Over the 35-day treatment period the team gave 1 ounce (the high-stress dose) of the supplement three times daily in each treatment group horse’s feed and a 1-ounce dose of placebo three times daily in each control horse’s feed. They were blinded to treatments to avoid bias in scoring and repeated gastroscopies and weight checks on Days 14, 28, and 35.

Supplement Effects on Gastric Ulcer Scores

Andrews and his team saw a significant weight increase in all horses, but the treatment did not affect body weight. The mean nonglandular EGUS and severity scores were significantly lower in the treatment group on Days 28 and 35.

“The nonglandular ulcers were healed, except for mild hyperkeratosis (callousing), on these dates as well,” Andrews said. “The mean glandular (ulcer) and severity scores were significantly lower after 14 days in the treatment group. The ulcers did heal, but some reoccurred in both groups of horses by Day 28, which is not uncommon in these types of ulcers.” The mean gastric fluid pH remained low and variable throughout the study in both groups. Many drugs when used long term block gastric acid, which can change the stomach’s physiology. In other words, this supplement contributed to gastric health without changing stomach acidity.

Take-Home Message

Based on the research, Andrews said he believes the schizophyllan and hyaluronan supplement might have uses for managing horses with EGUS long-term and/or in conjunction with appropriate pharmaceutical treatment. (Supplements shouldn’t be used to treat disease but improve stomach health after discontinuing pharmacologic agents, he added.) The researchers observed clear improvement in nonglandular and glandular ulcer scores in the treatment group and did not observe any adverse effects from the supplement. The horses also readily consumed it, he added.

Andrews noted study limitations were a small sample size with limited breeds, a short treatment period, and that horses were stalled without exercise—management approaches that can be risk factors for ulcers. He hopes to address these limitations in future studies by finding out if the schizophyllan and hyaluronan product acts synergistically (a combined positive effect) with omeprazole or other drugs to improve gastric health in horses as well as prevent gastric ulcer recurrence.

Approximately 40 million working donkeys worldwide play key roles in the daily household economics of developing countries. These animals are responsible for pulling heavy loads in carts, often with improperly fitting harnesses that apply pressure on the neck. This can cause tracheal collapse and respiratory disease.

Carts fashioned for the approximately 10,000 donkeys in Meru County, Kenya, have a single shaft with a crossbeam attached to the donkeys proximal (closer to the base) to middle neck. “This means the weight of the entire cart is placed on the donkey’s ventral (underside of the) neck, directly overlying the trachea,” said Martha Mellish, DVM, Dipl. ACT, of the Department of Health Management at Atlantic Veterinary College, in Prince Edward Island, Canada.

Recognizing the impact of improperly fitting harnesses on the health and welfare of working donkeys, Mellish and colleagues investigated the presence of upper airway injury and tracheal collapse in both cart and pack donkeys at a Meru County health clinic. She presented their results at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida.

Performing Endoscopy in Working Donkeys

The team used an endoscope to evaluate each donkey’s trachea, and blinded reviewers evaluated the videos to grade tracheal collapse and identify tracheal ring abnormalities. The researchers also noted the presence of ventral neck skin and hair abnormalities on physical examination, which could indicate an improperly fitted harness.

Although performing an endoscopy on donkeys is more technically challenging than in horses, Mellish reported being able to grade tracheas with an average of 21 seconds of endoscopic video of the trachea. In total they reviewed 80 videos and recorded that 66 were considered diagnostic—38 from cart donkeys and 28 from pack donkeys. They considered some videos to be nondiagnostic if mucous obscured the camera lens or they could not pass the scope deep enough into the trachea.

Investigating the Effects of Harness Placement in Working Donkeys

The video reviewers identified a high prevalence of Grade 3 tracheal collapse—where the diameter of the trachea is reduced by 50% to 75%—occurring in almost 40% of the cart donkeys. They did not diagnose any cart donkeys with Grade 4 (full) tracheal collapse. In contrast, no pack donkeys had Grade 3 or 4 tracheal collapse.

“We also found a strong association between tracheal collapse and tracheal ring abnormalities and pulling carts,” said Mellish. “It is possible that the repeated trauma to the cervical trachea caused the endoscopic findings.”

These tracheal abnormalities, she said, are a significant welfare concern; affected donkeys might struggle to breathe, have low oxygen levels, or be reluctant to work. This in turn might result in prodding or maltreatment from the driver.

In addition, two-thirds of the cart donkeys had hair loss and thickened skin on the ventral neck, which was positively associated with tracheal collapse.

Take-Home Message

Mellish and her team found that 40% of cart donkeys experienced a significant reduction in trachea size, which has a direct impact on the animals’ welfare. However, they did not observe the tracheal changes in pack donkeys. “These findings are a foothold for improving harness and cart design to improve welfare in this community,” she said.

Newly published Equine Viral Hepatitis Guidelines from the American Association of Equine Practitioners (AAEP) provide comprehensive information and instruction for equine veterinarians concerning transmission, risk factors, clinical signs, diagnostics, and other considerations for two viral causes of liver damage in horses: equine parvovirus-hepatitis (EqPV-H) and equine hepacivirus (EqHV).  

The guidelines document incorporates updates to guidance originally published for EqPV-H in 2021 along with new and corresponding guidance for EqHV, recently recognized as a cause of chronic hepatitis.  

While EqHV infects approximately 40% of US horses, versus 15% for EqPV-H, most will clear the infection within 20 weeks and will not have clinical signs of liver disease or illness. Approximately 20% of horses infected with EqHV will develop persistent infection lasting beyond six months, and a small percentage of those will develop hepatitis over months to years. Affected horses can have subclinical disease or show signs of liver disease of varying severity. Treatment of clinically affected horses relies primarily on supportive care and treatment of liver dysfunction. 

“Both viruses can be present and not actively causing disease. Serial testing and early testing can help veterinarians interpret whether either virus is likely to be the cause of hepatitis,” said guidelines author Joy Tomlinson, DVM, PhD, DACVIM, assistant professor of large animal medicine at the University of Pennsylvania School of Veterinary Medicine, in Kennett Square.  

“If you diagnose a horse with hepatitis, I recommend either submitting the serum PCR right away or saving serum from the first visit in your freezer,” she added. “If you decide to pursue viral testing later, having that sample to compare to will be very helpful.” 

The Equine Viral Hepatitis Guidelines were reviewed and approved by the AAEP’s Infectious Disease Committee and board of directors. View the guidelines or save them to your mobile device as a PDF for future reference at https://aaep.org/resource/equine-viral-hepatitis-guidelines. 

AAEP members may also access the guidelines through the AAEP On-the-Go app; search “AAEP On-the-Go” at your app store to download. 

In addition to the Equine Viral Hepatitis Guidelines, AAEP guidelines for more than 30 equine infectious diseases and foreign animal diseases are accessible through the app and the AAEP Guidelines Library at https://aaep.org/guidelines-resources/resource-library/guidelines-library.