On May 30, a 14-year-old mare at a boarding facility in Seminole County, Florida, tested positive for strangles. The horse developed clinical signs on April 11, including fever and nasal discharge. She is now recovering. 

In addition to the confirmed case, four horses are suspected positive, and 30 horses are exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

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)

With hurricane season upon us, horse owners must take proactive measures to ensure the safety and well-being of their animals. Here are some tips from the Louisiana State Animal Response Team (LSART), the Louisiana Department of Agriculture and Forestry, and the LSU School of Veterinary Medicine for horse owners to effectively prepare in areas prone to hurricane damage: 

Family Preparedness

Develop a personal plan with provisions for your entire family, including your animals, and update the plan yearly. Saving the Whole Family is a useful guide from the American Veterinary Medical Association (AVMA). 

Health and Identification

• Ensure your horse is up to date on his/her vaccinations against rabies, tetanus, and the encephalitis viruses (Eastern and Western equine encephalomyelitis, and West Nile virus).
• Establish a network and communication plan with the horse and farm animal-owning neighbors in your parish (or county, depending on where you live). Get to know one another, hold meetings to discuss various scenarios, and identify local resources for handling disaster situations. Be prepared to assist one another.
• Familiarize yourself with your parish (or county) emergency managers, who are responsible during emergencies. If you are a Louisiana resident visit gohsep.la.gov/ABOUT/STATE-REGIONS for specific contact information.
• Be sure your horse has two forms of identification: (1) Permanent identification such as a microchip, tattoo, or brand, and (2) A luggage-type tag secured to the tail and halter (be sure to use a leather halter for breakaway purposes). Fetlock tags are useful and can be acquired online or from a local farm supply store, or you can use a paint stick or nontoxic spray paint. Clearly legible tags should include your name, address, and phone number (preferably someone out of state in case of local phone outages).
• Keep a record of the microchip number (perhaps on your Coggins, which is your annual proof of a negative test for equine infectious anemia, or EIA) in an easily accessible location. It is advisable to keep a duplicate copy with a family member or friend in a distant location for safekeeping.

Evacuation Planning

• Always plan to evacuate if possible. Identify a destination and predetermine the routes well in advance. It is crucial to relocate your horses a sufficient distance from the coast—if you’re a Louisiana resident, that is preferably north of Interstate 10 and ideally north of Alexandria. Aim to evacuate at least 72 hours before the anticipated storm arrival. Avoid the risk of being stuck in traffic with a trailer full of horses and a looming hurricane. Share your evacuation contact information with your neighbors.

Emergency Preparedness

• Prepare a waterproof emergency animal care kit with all the items you normally use, including medications, salves or ointments, cohesive bandage (Vetrap or CoFlex), other bandages, tape, etc. Store the kit in a safe place where you can easily access it following a storm.
• Initiate early property cleanup to remove debris that could be tossed around by strong winds. Be careful of down live power lines that can pose a danger to people and animals.

Sheltering at Home

• The choice of keeping your horse in a barn or an open field is up to you. Use common sense, taking into consideration barn structure, trees, power lines, condition of surrounding properties, and the likelihood of the property and structure to flood. Farms subject to storm surge or flash flooding should turn their horses out so horses are less likely to get trapped and drown.
• Remove all items from the barn aisle and walls and store them in a safe place.
• Have at least a two-to-three-week supply of hay (wrapped in plastic or waterproof tarp) and feed (stored in plastic watertight containers, securing the container seams with duct tape). Place these supplies out of reach of floodwaters in the highest and driest area possible.
• Fill clean plastic garbage cans with water, secure the tops, and place them in the barn for use after the storm.
• Place an emergency barn kit containing a chain saw and fuel, hammer(s), saw, nails, screws, and fencing materials in a secure area before the storm hits so that it is easily accessible following the storm.
• Have an ample supply of flashlights and batteries and other nonperishable items.

Communications and Up-to-Date Information

• Listen to local radio stations in your area. If you have internet access, visit state-run websites that provide accurate status information (i.e., State Police, State University, Louisiana Department of Agriculture and Forestry) and take all cautions/warning serious and act accordingly.
• Visit the LSART website for more detailed information regarding horse hurricane preparations and other emergency and health-related information.  

If you’re a Louisiana resident and your animals need emergency medical care after hours, the LSU Veterinary Teaching Hospital on Skip Bertman Drive is available 24/7, 365 days a year. For pets and small exotics, call 225/578-9600, and for horses and farm animals, call 225/578-9500. While the LSU Veterinary Teaching Hospital typically remains open during hurricanes, please call first to be sure the hospital is accessible and veterinary teams are able to accept patients following a disaster. 

One horse at a private facility in Whatcom County, Washington, recently tested positive for pigeon fever. The horse had been colicky and nonresponsive and was euthanized. Necropsy revealed massive internal adhesions and abscessation.

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Pigeon Fever

Pigeon fever is a bacterial infection that affects cattle and horses. It can cause large abscesses, most commonly on the chest and under the belly. Horses become infected when bacteria enters through broken skin, such as small scrapes or wounds. Peak season for infection is late summer through fall.

Good horse health safety practices are key to limiting the spread of pigeon fever. These practices include:

• Fly control;
• Not sharing water buckets or equipment; and
• Avoiding tying horses in high-traffic areas.

If a horse owner suspects that their animal is affected, they should contact their veterinarian.

On June 3, a 23-year-old pony mare in Sonoma County, California, tested positive for equine herpesvirus myeloencephalopathy (EHM) secondary to equine herpesvirus-1 (EHV-1). The mare initially became ataxia on June 1. She was euthanized, and 36 potentially exposed horses on the home premises are under quarantine. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM.

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.

One foal at a stable in Estrie, Quebec, recently tested positive for rotavirus after presenting with diarrhea. It is unknown if other horses are exposed.

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

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. 

How a 21-year-old Hanoverian gelding stayed competitive at the Florida winter circuit

Many horse owners, riders, and trainers expect their horses’ athletic potential to diminish as they enter their later years; however, some horses remain healthy and happy in their work well past what many would consider their peak years. As horses age, they might experience more joint pain associated with osteoarthritis, digestive problems or a decline in gut health, or decreased performance. Fortunately, with advancements in equine medicine, veterinarians can work with horses’ trainers and care teams to help ensure long-term soundness.

The Crucial Equine Vet-Client-Patient Relationship

Successfully maintaining a horse in the top levels of competition throughout his later years requires a close relationship between the rider or trainer and veterinarian. “The rider is the person who spends the time on the horse’s back and feels differences in a gait transition or that a canter lead feels (different) one way versus the other,” says Kate Britton, DVM, of Atlantic Equine Services in Dover, New Hampshire, and Wellington, Florida.

These small details are crucial to the overall picture, especially when combined with information from the horse’s competition performance and a clinical exam. Meanwhile, don’t forget to keep the owner in the loop. “Keeping an open relationship with the owner is paramount to the health and success of the horse as they are the ones standing behind the horse with all parties involved on both good and bad days,” she adds. 

Maintaining Mindful at the Top Levels of Sport

Jennifer Hannan, rider and trainer, of Ocean Echo Farm in Wakefield, Rhode Island, and Wellington, has been training Mindful, a 21-year-old Hanoverian gelding owned by Selma Garber and Kensel LLC, since 2017. (Mindful started his US Equestrian-recognized showing career in 2013 with a different owner and riders.)

In their years together they have shown at the top venues around the country, such as Palm Beach International (now Wellington International), which Hannan says was the scene for their first international derby win as a pair. “He has since gone on to win seven international derbies at (Palm Beach/Wellington International). He has earned championships at every major horse show on the East Coast.”

Over the years Hannan and her veterinarian, Britton, have worked closely with one another to maintain Mindful’s physical and mental well-being at the highest levels of the sport.

Managing Mindful’s Joint Health

Britton regularly evaluates Mindful—typically monthly, she says, but twice monthly for performance evaluations during periods of intense competition. “Regarding maintenance care, we try to stay ahead of any issues, so (I see him) around four times per year for this.”

To manage any potential joint pain that could affect his performance, Britton treats him with intra-articular (IA) autologous protein solution and 2.5% polyacrylamide hydrogel (not at the same time) based on the results of her regular physical exams and soundness evaluations. “We try to stay ahead of any issues that may arise with his continued career, and we wanted to use the most beneficial treatments for his joints,” she says.

Equine Complementary Therapies and Nutrition

In addition to regular soundness examinations, Mindful also receives consistent veterinary chiropractic adjustments, acupuncture, and massage, which Britton says complement his medical treatments and play an important role in his longevity.

“He goes on a Theraplate daily and turns out as much as possible,” adds Hannan.

“His diet plays a role in his health as far as keeping him fit,” she continues. “We feed an all-natural diet, which is low in sugar, and I really feel like that has helped him in his career with me.” This consists of a forage-based diet (including alfalfa pellets and beet pulp) with non-GMO supplements to fill any nutritional gaps.

Utilizing Equine Fitness for Long-Term Soundness

Hannan works to keep Mindful physically fit year-round to help him maintain a healthy muscular condition and always stay comfortable in his work. “His overall fitness is our main goal,” she says. “We try to keep him fit and happy.”

Mindful stays in a consistent program with a balance of jumping and discipline-specific training days, along with relaxed trail riding and hacking days. “I think it’s important to keep him fit on many different types of surfaces,” says Hannan. “He works in the fields with hills as well as in the ring and even some harder surfaces.” However, Mindful only jumps once a week.

“That may include cavalletti exercises or just a few jumps, so he keeps his fitness,” Hannan adds, noting she rarely schools Mindful over show-height fences, but she might do so once before a show.

She adds that Mindful’s owner allows her to create a detailed training and competition plan for him, without ever pushing him past his physical or mental limits and while keeping his competition schedule light. “We have really been able to tailor his show schedule, physical fitness, and overall soundness (to his individual needs),” says Hannan. “I truly believe all of this has made a huge impact on his unbelievable career.”

Take-Home Message

Caring for horses that continue competing into their senior years demands a close relationship between the riders or trainers and veterinarians as well as careful daily monitoring of any minor changes in the horses’ behavior.

“Always listen to your horse and trust your feeling of them and what they are telling you,” says Britton. “Jenny has an exceptional ability to know minor changes in how her horses are feeling, which I feel helps keep them ahead of major issues.”

Trainers and veterinarians must maintain open communication regarding a horse’s health and performance to keep him sound and happy long-term.

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.

On May 28, one horse in Clearwater County, Alberta, was confirmed positive for equine infectious anemia (EIA). The horse was tested after developing clinical signs of disease. Initial reports indicate that there are several other horses on the property. The infected horse and all exposed horses are under quarantine. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About EIA

Equine infectious anemia is a viral disease that attacks horses’ immune systems. The virus is transmitted through the exchange of body fluids from an infected to an uninfected animal, often by blood-feeding insects such as horseflies. It can also be transmitted through the use of blood-contaminated instruments or needles.

A Coggins test screens horses’ blood for antibodies that are indicative of the presence of the EIA virus. Most U.S. states require horses to have proof of a negative Coggins test to travel across state lines.

Once an animal is infected with EIA, it is infected for life and can be a reservoir for the spread of disease. Not all horses show signs of disease, but those that do can exhibit:

• Progressive body condition loss;
• Muscle weakness;
• Poor stamina;
• Fever;
• Depression; and
• Anemia.

EIA has no vaccine and no cure. A horse diagnosed with the disease dies, is euthanized, or must be placed under extremely strict quarantine conditions (at least 200 yards away from unaffected equids) for the rest of his life.

On May 29, a 2-year-old Thoroughbred colt in Barn 85 at the Saratoga Race Course in Saratoga County, New York, tested positive for strangles. The horse was shipped to Rood & Riddle Equine Hospital on May 28 for evaluation and treatment of a respiratory infection. He began treatment immediately and was transported from the hospital to a private layup facility. 

Barn 85 is now under quarantine. A 24-hour security watch has been established, and all horses in the barn will receive regular temperature checks. The horses under quarantine are not permitted to enter races or train among the general horse population. Asymptomatic horses in Barn 85 will have isolated training hours at the Oklahoma Training Track following the close of training for the general horse population at 10 a.m. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

The State Department of Agriculture recently confirmed that one horse in Hall County, Georgia, is positive for pigeon fever. The horse is under voluntary quarantine. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Pigeon Fever

Pigeon fever is a bacterial infection that affects cattle and horses. It can cause large abscesses, most commonly on the chest and under the belly. Horses become infected when bacteria enters through broken skin, such as small scrapes or wounds. Peak season for infection is late summer through fall.

Good horse health safety practices are key to limiting the spread of pigeon fever. These practices include:

• Fly control;
• Not sharing water buckets or equipment; and
• Avoiding tying horses in high-traffic areas.

If a horse owner suspects that their animal is affected, they should contact their veterinarian.

A 2-week-old foal in Région de Gatineau, Quebec, recently tested positive for rotavirus after developing diarrhea and hepatitis. The foal is recovering, and one additional case is suspected. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

On May 24, a 26-year-old Arabian gelding at a boarding facility in Niagara County, New York, tested positive for strangles. The horse developed clinical signs on May 21, including fever and inappetence. Two additional cases are suspected, and 15 horses are exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On May 22, a 6-year-old Mustang gelding in Eaton County, Michigan, tested positive for strangles. The horse developed clinical signs on May 12, including nasal discharge and swollen submandibular lymph nodes. He is now under quarantine. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

Three horses at a boarding facility in Marion County, Florida, recently tested positive for strangles. The affected horses are under quarantine, and 50 additional horses are exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On May 22, a 4-year-old Thoroughbred gelding at a boarding facility in Montgomery County, Pennsylvania, tested positive for strangles. The horse developed clinical signs on May 19, including fever and nasal discharge. He is under quarantine, and 39 horses are exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On May 22, a 20-year-old Quarter Horse mare in Cumberland County, Pennsylvania, tested positive for Potomac horse fever. The horse, who is vaccinated, developed clinical signs on May 18, including fever and colic signs which progressed to liquid diarrhea. She was referred to a hospital in Virginia, where she is responding to medical management.

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Potomac Horse Fever

Potomac horse fever is caused by Neorickettsia risticii, an organism found in parasites, called flukes (flatworms), that infects aquatic snails and insects. Horses can be infected by ingesting insects carrying Potomac horse fever or by drinking water containing N. risticii. Additionally, horses can get Potomac horse fever by inadvertently consuming infected insects or parasites in feed, water, or on pasture.

The incubation period for Potomac horse fever is between one and three weeks, and the mortality rate is up to 30%. While vaccines against Potomac horse fever are not 100% effective, vaccinated horses tend to have fewer and less severe clinical signs.

Most Potomac horse fever cases are reported in July through September, and outbreaks tend to be seasonal.

Horse owners and caretakers, especially those who keep their horses near creeks and rivers, should watch for signs including:

• Diarrhea
• Colic
• Loss of appetite
• Lethargy
• Toxic shock
• Dehydration
• Abortion in pregnant mares
• Laminitis
• Mild to severe fever.

On May 20, a 25-year-old mare at a boarding facility in the Regional Municipality of Halton, Ontario, tested positive for strangles. The mare developed a thick nasal discharge and cough after sharing a paddock with four new horses. She is now under quarantine. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

Two horses in Florida recently tested positive for strangles. The horses live in Charlotte and Walton counties. 

In Charlotte County, a 14-year-old Quarter Horse gelding tested positive on May 20 after developing nasal discharge. He is under quarantine, and one additional horse is suspected positive. 

In Walton County, an 8-year-old Thoroughbred gelding tested positive on May 20 after developing a lymph node abscess on May 15. One additional horse is suspected positive, and four horses are exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

Six horses at a premises in Los Angeles County, California, recently tested positive for equine herpesvirus-1 (EHV-1). 

Two horses—a 20-year-old Thoroughbred mare and a 28-year-old warmblood mare—were reported positive on May 16. The 20-year-old mare was euthanized, and 95 exposed horses were placed under quarantine. 

Since then, four additional horses have tested positive, including a 3-year-old gelding, a 20-year-old mare, a 21-year-old warmblood mare, and a 24-year-old Quarter Horse mare. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM.

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.

One horse at a private facility in King County, Washington, recently tested positive for pigeon fever. No additional details are currently available. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Pigeon Fever

Pigeon fever is a bacterial infection that affects cattle and horses. It can cause large abscesses, most commonly on the chest and under the belly. Horses become infected when bacteria enters through broken skin, such as small scrapes or wounds. Peak season for infection is late summer through fall.

Good horse health safety practices are key to limiting the spread of pigeon fever. These practices include:

• Fly control;
• Not sharing water buckets or equipment; and
• Avoiding tying horses in high-traffic areas.

If a horse owner suspects that their animal is affected, they should contact their veterinarian.

One horse at a stable in Mirabel, Quebec, recently tested positive for equine influenza after developing a cough and light nasal discharge. The horse is under quarantine. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Equine Influenza

Equine influenza is a highly contagious respiratory disease that infects horses, ponies, and other equids, such as donkeys, mules, and zebras. The virus that causes it is spread via saliva and respiratory secretions from infected horses. Horses are commonly exposed via horse-to-horse contact; aerosol transmission from coughing and sneezing; and contact with humans’ contaminated hands, shoes, or clothes or contaminated tack, buckets, or other equipment.

Clinical signs of equine influenza infection can include a high fever (up to 106°F); a dry, hacking cough; depression; weakness; anorexia; serous (watery) nasal discharge; and slightly enlarged lymph nodes. Consider monitoring your horse’s health at shows by taking his temperature daily, which can help you pick up on signs of infection early and take appropriate measures to reduce disease spread.

​Vaccination is an important and inexpensive way to protect your horse. US Equestrian requires proof that horses have had an equine influenza vaccination within the six months prior to attending organization-sanctioned competitions or events. Your veterinarian can help you determine what other vaccines your horse might benefit from.

In addition to vaccinating, following strict biosecurity protocols can help reduce your horse’s chance of infection and disease. Such measures include quarantining new equine arrivals at barns, disinfecting buckets and equipment, and preventing nose-to-nose contact between horses.

People say good school horses are worth their weight in gold. Here’s what it takes to maintain the equine industry’s most valuable teachers.

How do you preserve your school horses’ health, soundness, and well-being long-term? This difficult question challenges every good horseman, says Jesslyn Bryk-Lucy, DVM, cAVCA, professor of equine studies and resident veterinarian at Centenary University, in Long Valley, New Jersey, where she manages the daily medical needs of the school’s approximately 85-horse herd.

Riding school owners like Nina Leeds, who runs Manor Hill Farm in Nicholson, Pennsylvania, constantly face the challenge of balancing their ponies’ and horses’ health and welfare with the financial pressures of their business. “You must do right by your equine employees,” she says.

Let’s take a closer look at the challenges and unique needs of riding school mounts.

School Horses’ Unique Challenges

Unlike a privately owned pleasure horse that’s not expected to pay for himself, school horses must earn their keep, generating enough income to cover their own care. But despite widespread stigma, a riding school job doesn’t necessarily equal subpar access to equine health care. In Bryk-Lucy’s collegiate program, where horses train and compete in the hunter/jumper and dressage disciplines, these equine professors have access to top-of-the-line care—a prime example being regular chiropractic and acupuncture treatments.

Nonetheless, these animals deal with stressors specific to their school horse status. “Inconsistency of riders is undoubtedly the biggest challenge,” Leeds admits. “These individuals must be forgiving and adaptable. Most of the time their student riders are still working on the basics and, as a result, may unintentionally sit crooked, add more pressure to one rein than another, etc.,” she says. “This can be habit-forming for the horses, causing them to travel incorrectly and creating compensatory pain over time.”

Adding to the challenge, she says, most ponies get ridden by children of varying skill levels because small, light, and experienced adult riders are hard to find.

Different Jobs, Similar Needs

Despite their occupational challenges, school horses have the same physiological needs as any other horse. “I manage the 85 school horses like any privately owned horse in my ambulatory practice,” says Bryk-Lucy, who also owns Leg Up Equine Veterinary Services in northern New Jersey. “The issues that I often have to manage—arthritis, sore backs, chronic soft tissue injuries, navicular syndrome, etc.—are the same pathologies (disease/damage) I see in private practice.”

Starting with the basics, school horses need suitable forage-based nutrition, sufficient turnout, proper grooming, regular dentistry and hoof care, and appropriate vaccination and deworming. In 2021 Bryk-Lucy’s then-student Abigail Reilly found that university horses turned out for at least 12 hours a day had a 25% lower incidence of soft tissue injuries than those turned out for less time¹. Researchers on a French study looking at 184 school horses found housing had the biggest impact on the animals’ emotionality level, a factor affecting their suitability to teach riders of varying levels². The data underscore the importance of species-appropriate care, including turnout and social contact for school horses.

Recognizing Signs of Pain in School Horses

Many school horses are hardy and stoic, making it easy to overlook signs of distress and discomfort. Pain can also manifest in subtle ways, which is why Bryk-Lucy relies on the staff and students to alert her to any potential issue with a university-owned horse. In her experience, early detection can have a significant positive effect on the horse’s recovery.

“Some common complaints that prompt an exam are an evasive response suggesting back soreness when being brushed, crabbiness when grooming and tacking, mounting block issues, reluctance to move forward, refusing jumps, favoring a lead, swapping (leads) before a jump, missing a lead change, running on the landing of a jump, tripping, etc.,” she says.

“In our lesson program we try to rule out pain as a cause of the behavior before classifying that behavior as a training issue,” she adds. In another study, the same French authors mentioned earlier found school horses were less likely to exhibit back disorders if managed by attentive caretakers who tend to overevaluate potential back pain³.

Essentially, scientists have shown attention to subtle changes in horses’ demeanors and getting the vet involved early pays off.

Limitations And Expectations

“Like most riding school programs, we have quite a few ponies that come to us as a step-down job from their competition careers with preexisting limitations,” Leeds says. She credits their long-term success to resisting the urge to push these schoolmasters when they are seemingly going so well.

“If our veterinarian has advised us that a pony should be used for flatwork only, not be longed, etc., there are no exceptions for us,” she adds. “It’s tempting when you are in a pinch, but ultimately pushing them past what is advisable, even as a once-in-a-while exception to the rule, can be detrimental to the goal of a long, productive career.”

Leeds says she’s found that teaching true horsemanship helps minimize wear on her ponies while still allowing her to run a large, successful program. Here again, setting expectations and prioritizing horse welfare remain key. “My students do not expect to jump every day, jump huge fences, or ride in extreme temperatures,” she says. “Our goal is to teach them that the animal must always come first. In turn, we can provide a more realistic workload for the lesson ponies.”

Further, Leeds emphasizes correct flatwork and small jumps with more technical exercises, and she turns to activities such as groundwork sessions and trail rides on extremely hot or cold days. For both their physical and mental well-being, she’s found it helpful to introduce variety in school horses’ work while limiting longe-line lessons because repeatedly traveling in circles adds strain to the musculoskeletal system.⁴

Money Matters

The stakes are high for the barn owner who depends on lesson income to feed and care for all her in-work, laid-up, and retired school horses and pay for and maintain the property. In France students often purchase an annual riding school pass with a fee to fund the school horses’ retirements. In the U.S. some establishments are switching from a no-commitment pay-per-lesson billing method to a semester-long subscription system, eliminating the sometimes devastating unpredictability of fluctuating monthly income. Some early adopters of the practice point out that school horses need to eat regardless of whether students attend their scheduled sessions.

We turned to Bryk-Lucy to describe the common physical limitations of school horses. “Beyond soft tissue and joint injuries, I see a lot of back soreness,” she says, pointing out that these animals typically carry different saddles and riders daily. Under her care university horses with chronic back pain get their own saddles. The rest get time off, non-steroidal anti-inflammatory drugs (NSAIDs) such as phenylbutazone (Bute) or firocoxib, methocarbamol (a muscle relaxer), acupuncture, and chiropractic care. “These individuals usually return to work and are monitored and managed closely,” she says. However, if one needs shock wave therapy or regenerative therapies, she must refer to an outside practice, which she says isn’t always cost-effective for such a large herd.

Beyond her own expectations, Bryk-Lucy must also manage those of the faculty, staff, and students. “The reality is these donated horses are on their second or third career; they may come to us with a stiff hind end, good and bad days, etc.,” she says. As long as horses are comfortable and willing to work,and the slight gait abnormality (also called a mechanical lameness) does not worsen, she allows them to keep doing their job.

“I prepare the faculty, staff, and students to expect these individual variations in certain horses and educate them on what to look for to identify a new or worsening condition,” she says. There’s an upside, though. “Sometimes soundness issues in a low-level riding program are not as limiting as they once were on the show circuit because the horses are doing an easier job, and then I don’t have to manage anything!”

What Makes or Breaks School Horse Soundness

Bryk-Lucy says some of the big considerations that affect school horses’ ability to stay sound for the long haul include:

• Limiting rider weight to no more than 20% of the school horse’s body weight, because researchers have found exceeding this can temporarily cause lameness⁵.
• Maintaining fitness. Researchers have shown hippotherapy horses better tolerate heavier riders when fi tter⁶. “Fit horses are better able to handle their workload and less likely to sustain a soft tissue injury,” Bryk-Lucy says. “Some of our university horses are off for the summer and winter breaks. We are very careful and strategic with their return to work to ensure they are fi t enough for the first intercollegiate horse show, generally four to six weeks after the start of the semester.”
• Imposing limits on how often and how high horses jump. In a 2010 study of eight school horses, researchers in the Netherlands confirmed via blood tests what professionals already knew—jumping, even at a low level, significantly increases workload compared to cantering the same distance and speed without jumps⁷.
• Scheduling lessons so school horses have rest days and time off to recover. In 2023 researchers published data suggesting that following an increase in work hours, school horses show a greater degree of behaviors that can be interpreted as either fatigue or discomfort using the Horse Grimace Scale (HGS)⁸. Trainers must provide proper recuperation time to support career longevity.
• Choosing the appropriate level for use in a riding program, considering previous injuries, age, soundness, and suitability. “The horses that successfully work for a long time start at upper levels and slowly teach less experienced riders as they age (and need to step down),” Bryk-Lucy says. “These horses can continue to earn their keep as they age gracefully, fulfilling multiple roles as their career progresses.”
• Keeping up with maintenance as needed and addressing health and soundness issues early. At Manor Hill Leeds’ vet evaluates her ponies at least twice a year when it’s spring and fall vaccination time.

Leeds has found workload to be the most significant factor affecting a school horse’s career longevity. “Overloading an individual with a jampacked schedule risks leaving them physically sore and mentally burnt out,” she says. “Being realistic about how many students you can take with your current lesson stock is important,” she adds, tying back to the importance of keeping expectations in check.

“Pushing your lesson horses beyond reasonable risks harms both your animals and your means of making an income, potentially resulting in horses needing significant downtime and incurring vet bills,” she adds. To find the right balance, she grew her program gradually, accepting more students only as she could find more ponies to join her team.

Final Thoughts on School Horse Soundness

People say good school horses—reliable, adaptable, forgiving, and sure-footed—are worth their weight in gold. Our sources establish a few truths about the noble fourlegged teachers in riding schools: They need to earn their keep. They are athletes and should be treated accordingly, and they face unique challenges tied to their occupation. Ultimately, school horses form the foundation of our equestrian sport and deserve our commitment to a lifetime of care.

References

1. Reilly AC and Bryk-Lucy JA. Incidence of soft tissue injury and hours of daily paddock turnout in non-elite performance horses. 2021 Equine Science Society Virtual Symposium. tinyurl.com/6z75a9mw

2. Lesimple C, Fureix C, LeScolan N, Richard-Yris MA, Hausberger M. Housing conditions and breed are associated with emotionality and cognitive abilities in riding school horses. Appl Anim Behav Sci. 2011;129(2-4):92-99.

3. Lesimple C, Fureix C, Biquand V, et al. Comparison of clinical examinations of back disorders and humans’ evaluation of back pain in riding school horses. BMC Vet Res. 2013;9:209.

4. Logan AA, Nielsen BD, Robison CI, Hallock DB, Manfredi JM, Hiney KM, Buskirk DD, Popovich JM. Impact of gait and diameter during circular exercise on front hoof area, vertical force, and pressure in mature horses. Animals. 2021;11(12):3581.

5. Dyson S, Ellis AD, Mackechnie-Guire R, Douglas J, Bondi A, Harris P. The influence of rider: horse bodyweight ratio and rider-horse-saddle fit on equine gait and behaviour: a pilot study. Equine Vet Educ. 2020;32(10):527-539.

6. De Oliveira K, Clayton HM, Dos Santos Harada É. Gymnastic training of hippotherapy horses benefits gait quality when ridden by riders with different body weights. J Equine Vet Sci. 2020;94:103248.

7. Sloet Van Oldruitenborgh-Oosterbaan MM, Spierenburg AJ. The workload of ridingschool horses during jumping. Equine Vet J. 2006;38(S36):93-97.

8. Ijichi C, Wilkinson A, Riva MG, Sobrero L, Dalla Costa E. Work it out: investigating the effect of workload on discomfort and stress physiology of riding school horses. Appl Anim Behav Sci. 2023;267:106054.

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.

Weighing Benefits Versus Risks

To boot or not to boot? The choice to cover a horse’s legs—and with what—­depends on many factors unique to each horse.

A main consideration is whether the horse has a specific need for protection, says Marlin, based on a previous injury, for example. Maybe he’s had issues with overreach and clips his forelimbs with his hind limbs. Or she’s got scrapes on the inner fetlocks where the opposite foot strikes. “If that shoe hits the inner fetlock just right, you can get a chip fracture,” he says.

Horses at high risk of colliding with structures other than their own feet—such as cross-country obstacles or show jumping fences taken at high speeds—also need protection. Horses hacking out through thick brush or on rocky paths need boots, at the very least to protect their skin from injury.

Hill believes it makes sense to follow the lead provided in human sports. “Human athletes use compression sleeves, tape, or braces to provide some support to areas that are unstable or a source of chronic issues, and I don’t recall those applications being shown to their detriment,” he says. Horses with chronic issues might still be able to have active careers with a bit of leg support, he says, and wrapping could help stabilize more recent injuries while they heal.

Warning Signs

Our sources agree: When used correctly, boots and wraps should only help, not harm. While researchers are still working on practical recommendations for their use, riders can take precautions to ensure these pieces of equipment aren’t causing new problems.

Polo wraps must be applied with just the right amount of tension—a skill riders can learn from experienced horse people, veterinarians, or physical therapists, says Hill. Any inflammation or swelling could suggest the wrap was too tight, he says.

Wet wraps might lose elasticity and trap moisture, putting the horse at risk of dermatitis (skin inflammation), Hill adds. Never apply a wet wrap. If the wrap gets wet during exercise, riders can complete the session, remove the wrap, and dry the leg.

As for boots, they shouldn’t slip, but they also shouldn’t be overtight, says Marlin. “Try putting an ankle bandage on, and make it really tight over your Achilles tendon,” Marlin says. “Then go for a run and see how that feels. You won’t do it to your horse again.”

Riders must also consider external factors, he adds. “The hotter the weather, the thicker the boot (especially foam or fleece types), the harder or longer the exercise, the hotter the tendons are going to get,” Marlin says.

Take-Home Message

Riders often apply boots and wraps to their horses’ legs for protection. But science still struggles to support manufacturers’ claims that boots and wraps help prevent certain injuries, and some researchers suggest they might increase the risk of tendon injury. Until evidence provides clearer guidelines, riders can aim to use properly applied boots and wraps wisely, recognizing their potential benefits and risks.

Editor’s note: This article was originally published in the Riding Horse 2023 issue.

A 27-year-old Arabian mare at a boarding facility in Dane County, Wisconsin, recently tested positive for strangles after developing clinical signs on May 8. She is under quarantine, and 50 horses are potentially exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On May 6, a 4-year-old Paint mare in Rogers County, Oklahoma, tested positive for equine herpesvirus-1 (EHV-1). She developed clinical signs on May 2, including hind limb weakness, urine retention, and recumbency. The mare was euthanized, and 10 exposed horses are under quarantine.

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM.

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.

Two horses in Los Angeles County, California, recently tested positive for equine herpesvirus-1 (EHV-1). 

The first horse was a 20-year-old Thoroughbred mare, who eventually developed equine myeloencephalopathy (EHM) secondary to EHV-1 infection. The mare was euthanized. 

The second horse is a 28-year-old warmblood mare who tested positive for EHV-1 after developing a fever. She is still alive. 

In addition to the two confirmed cases, 95 horses on the premises are potentially exposed. They are quarantined, and the California Department of Food and Agriculture is actively monitoring the situation.

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM.

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.

A 7-year-old Quarter Horse gelding in Wellington County, Ontario, recently tested positive for equine influenza. The horse was at a barrel racing event in Huron County and developed a fever after returning home on May 11. He is now recovering, and two additional cases are suspected. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Equine Influenza

Equine influenza is a highly contagious respiratory disease that infects horses, ponies, and other equids, such as donkeys, mules, and zebras. The virus that causes it is spread via saliva and respiratory secretions from infected horses. Horses are commonly exposed via horse-to-horse contact; aerosol transmission from coughing and sneezing; and contact with humans’ contaminated hands, shoes, or clothes or contaminated tack, buckets, or other equipment.

Clinical signs of equine influenza infection can include a high fever (up to 106°F); a dry, hacking cough; depression; weakness; anorexia; serous (watery) nasal discharge; and slightly enlarged lymph nodes. Consider monitoring your horse’s health at shows by taking his temperature daily, which can help you pick up on signs of infection early and take appropriate measures to reduce disease spread.

​Vaccination is an important and inexpensive way to protect your horse. US Equestrian requires proof that horses have had an equine influenza vaccination within the six months prior to attending organization-sanctioned competitions or events. Your veterinarian can help you determine what other vaccines your horse might benefit from.

In addition to vaccinating, following strict biosecurity protocols can help reduce your horse’s chance of infection and disease. Such measures include quarantining new equine arrivals at barns, disinfecting buckets and equipment, and preventing nose-to-nose contact between horses.

One horse in Grays Harbor County, Washington, recently tested positive for strangles. The horse lives at a private facility, and it is unknown if additional horses are exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On April 29, a 5-year-old Quarter Horse mare used for barrel racing in Garvin County, Oklahoma, tested positive for equine infectious anemia (EIA). The horse was tested due to a trace from an off-premises exposure. She was euthanized, and 38 additional horses are potentially exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About EIA

Equine infectious anemia is a viral disease that attacks horses’ immune systems. The virus is transmitted through the exchange of body fluids from an infected to an uninfected animal, often by blood-feeding insects such as horseflies. It can also be transmitted through the use of blood-contaminated instruments or needles.

A Coggins test screens horses’ blood for antibodies that are indicative of the presence of the EIA virus. Most U.S. states require horses to have proof of a negative Coggins test to travel across state lines.

Once an animal is infected with EIA, it is infected for life and can be a reservoir for the spread of disease. Not all horses show signs of disease, but those that do can exhibit:

• Progressive body condition loss;
• Muscle weakness;
• Poor stamina;
• Fever;
• Depression; and
• Anemia.

EIA has no vaccine and no cure. A horse diagnosed with the disease dies, is euthanized, or must be placed under extremely strict quarantine conditions (at least 200 yards away from unaffected equids) for the rest of his life.

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. 

On May 8, a yearling Paint colt in Eaton County, Michigan, tested positive for strangles. The colt developed clinical signs on March 28, including fever and enlarged lymph nodes. He is now under quarantine.

Two ponies on the same premises previously tested positive for strangles in February. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On May 5, a 7-year-old Thoroughbred gelding in Marion County, Florida, tested positive for strangles. The horse is under quarantine, and one additional horse is exposed.

This is Florida’s 18^th confirmed strangles case in 2025. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

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.”

The North Carolina Department of Agriculture’s Veterinary Division recently confirmed that one horse in Beaufort County has tested positive for strangles. No additional details are currently available. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On May 2, a 2-year-old filly in Buffalo County, Wisconsin, tested positive for strangles. The filly developed clinical signs on March 28, including fever and submandibular lymph node abscess. She is under quarantine, and two additional horses are exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On May 5, two horses in St. Clair County, Michigan—a 5-year-old Paint gelding and a 5-year-old warmblood gelding—tested positive for strangles. Both horses developed clinical signs on April 24, including fever and nasal discharge. They are under quarantine. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

Two horses in Maryland—one in Carroll County and one in Cecil County—recently tested positive for strangles. In addition to the two confirmed cases, 20 horses in Carroll County and 50 horses in Cecil County are potentially exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

One horse in Chesterfield County, Virginia, recently tested positive for equine infectious anemia (EIA) during a routine Coggins test. The horse is quarantined on the property and reportedly does not pose a risk to other horses in the area. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About EIA

Equine infectious anemia is a viral disease that attacks horses’ immune systems. The virus is transmitted through the exchange of body fluids from an infected to an uninfected animal, often by blood-feeding insects such as horseflies. It can also be transmitted through the use of blood-contaminated instruments or needles.

A Coggins test screens horses’ blood for antibodies that are indicative of the presence of the EIA virus. Most U.S. states require horses to have proof of a negative Coggins test to travel across state lines.

Once an animal is infected with EIA, it is infected for life and can be a reservoir for the spread of disease. Not all horses show signs of disease, but those that do can exhibit:

• Progressive body condition loss;
• Muscle weakness;
• Poor stamina;
• Fever;
• Depression; and
• Anemia.

EIA has no vaccine and no cure. A horse diagnosed with the disease dies, is euthanized, or must be placed under extremely strict quarantine conditions (at least 200 yards away from unaffected equids) for the rest of his life.

Two horses in Ontario recently tested positive for strangles. The horses live in Dufferin and Brant counties. 

In Dufferin County, a 12-year-old warmblood gelding developed an abscess on the outside aspect of his jaw, which was positive for S. equi. The horse is under voluntary quarantine. 

In Brant County, a 7-year-old Quarter Horse gelding developed a fever and nasal discharge shortly after returning from a competition in the Hamilton region. The nasal discharge tested positive for S. equi. One other horse on the property has since developed clinical signs. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

Seventeen horses in Texas recently tested positive for equine infectious anemia (EIA), including six in Wise County, one in Montague County, one in Hood County, one in Wharton County, five in Brazos County, one in Van Zandt County, and two in Cooke County. 

The positive horses have all either been quarantined or euthanized. The Texas Animal Health Commission is working closely with the owners and local veterinarians to monitor potentially exposed horses and implement biosecurity measures. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About EIA

Equine infectious anemia is a viral disease that attacks horses’ immune systems. The virus is transmitted through the exchange of body fluids from an infected to an uninfected animal, often by blood-feeding insects such as horseflies. It can also be transmitted through the use of blood-contaminated instruments or needles.

A Coggins test screens horses’ blood for antibodies that are indicative of the presence of the EIA virus. Most U.S. states require horses to have proof of a negative Coggins test to travel across state lines.

Once an animal is infected with EIA, it is infected for life and can be a reservoir for the spread of disease. Not all horses show signs of disease, but those that do can exhibit:

• Progressive body condition loss;
• Muscle weakness;
• Poor stamina;
• Fever;
• Depression; and
• Anemia.

EIA has no vaccine and no cure. A horse diagnosed with the disease dies, is euthanized, or must be placed under extremely strict quarantine conditions (at least 200 yards away from unaffected equids) for the rest of his life.

One horse at a private facility in Challam County, Washington, recently tested positive for equine influenza. The horse is under quarantine, and two additional cases are suspected.  

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Equine Influenza

Equine influenza is a highly contagious respiratory disease that infects horses, ponies, and other equids, such as donkeys, mules, and zebras. The virus that causes it is spread via saliva and respiratory secretions from infected horses. Horses are commonly exposed via horse-to-horse contact; aerosol transmission from coughing and sneezing; and contact with humans’ contaminated hands, shoes, or clothes or contaminated tack, buckets, or other equipment.

Clinical signs of equine influenza infection can include a high fever (up to 106°F); a dry, hacking cough; depression; weakness; anorexia; serous (watery) nasal discharge; and slightly enlarged lymph nodes. Consider monitoring your horse’s health at shows by taking his temperature daily, which can help you pick up on signs of infection early and take appropriate measures to reduce disease spread.

​Vaccination is an important and inexpensive way to protect your horse. US Equestrian requires proof that horses have had an equine influenza vaccination within the six months prior to attending organization-sanctioned competitions or events. Your veterinarian can help you determine what other vaccines your horse might benefit from.

In addition to vaccinating, following strict biosecurity protocols can help reduce your horse’s chance of infection and disease. Such measures include quarantining new equine arrivals at barns, disinfecting buckets and equipment, and preventing nose-to-nose contact between horses.

Mares can get a bad rap for recalcitrant estrous behavior, but hormones and tumors could also be at play

Anormal mare should behave just like any other horse. So says Paula Hitzler, longtime farm manager at the Michigan State University Horse Teaching and Research Center, in Lansing.

Over her 35 years at the center, home to one of the nation’s oldest Arabian horse breeding programs, Hitzler has seen herds of as many as 125 horses. When The Horse spoke with Hitzler in early 2024, the herd size was 68. Though just 15 of those horses were broodmares, most of the horses kept at the farm are mares because colts are typically sold after they’re started under saddle.

“In my opinion, (with a) normal mare, you should not know by working with her if she’s a mare or a gelding,” Hitzler says. “She should just be a solid citizen.”

Even in estrus it’s rare for otherwise pleasant, healthy mares to display sour temperament, Hitzler says.

“I don’t think that very many mares are ‘mareish,’ ” Hitzler says. Behaviors such as being grouchy, showing signs of heat around people, or urinating while being groomed—“I don’t see very much of that.”

Rather than ignoring or blowing off grouchy behavior as a normal side effect of heat cycles, Hitzler sees “bad” behavior as a potential warning sign that something has gone awry in the mare’s body; maybe the mare’s hormones are out of whack, or maybe the mare has an ovarian tumor. And, of course, mares can experience other ailments, such as injuries, gastric ulcers, or infections. Authors of a 2023 case series on behavioral disorders in mares with ovarian disorders reported that veterinarians must exclude nonreproductive causes of unwanted behavior and reduced performance, such as urinary tract disorders (vaginitis, pneumovaginitis, cystitis, and urolithiasis) and low-grade musculoskeletal pain. Because owners mentioned poor rideability, vets must also rule out rider factors¹.

What Is ‘Normal’ Behavior for Mares During Estrus?

Healthy breeding-age mares spend 15 to 17 days out-of-heat and five to seven days in heat, spring to fall (some sources say 14 to 16 days). Signs that a mare is in heat include receptivity to a stallion (standing when he’s around, for example), frequent urination, raising the tail, and “winking” the vulva.

Whether you find that behavior annoying or problematic depends partly on your perspective and priorities.

If you’re looking to breed your mare, obvious signs she’s in heat make your job easier—so long as the signs of heat reflect reality. If the mare is showing signs of estrus but is not in heat, then timing insemination or breeding could prove tricky.

While Hitzler’s perspective is that grouchy, sour estrous behavior isn’t super common among healthy mares, there’s long-standing scientific literature that says many horse owners feel otherwise. For people who show or compete their mares, when estrous signs do include being difficult to ride or handle, that can be frustrating.

“I did have one grouchy mare we put on Regu-Mate (altrenogest) while we were riding her just to suppress estrous behavior so she wasn’t so grouchy,” Hitzler says.

The drug keeps mares from coming into heat, and it can be useful during competition season.

Evaluating the Mare

If you’re concerned about mareish behavior, pay attention to the frequency, note it on your calendar, and call your veterinarian.

After assessing behavior, practitioners typically examine the mare’s reproductive tract, via palpation and ultrasound, for any irregularities, checking the ovaries’ appearance, relevant structures during the breeding season, and hormone levels to determine her heat cycle stage.

Trouble Ovulating?

When a mare seems to be in heat for longer than expected, it could be she is having trouble ovulating.

It turned out that one of Hitzler’s few “grouchy” mares that pinned her ears during cinching and was irritated by rider leg pressure was in persistent estrus—basically, the ovarian follicle was still developing and had not released the oocyte.

“Upon evaluation using rectal palpation and ultrasound, a persistent follicle was observed,” Hitzler recalls. “Thankfully, a dose of hCG resolved the issue. Sometimes the persistent follicle will not respond to medications. We were thankful that the mare did not have an ovarian tumor.”           

Ovaries and Tumors

Indeed, ovarian tumors can cause behavioral issues, and vets can confirm these growths with ultrasound or hormone testing.

Removing an ovary when there’s a tumor is an obvious choice. Some owners remove ovaries based on behavioral problems even when a tumor has not yet been confirmed.

In the July 2023 study mentioned above, researchers at the Veterinary Teaching Hospital of the University of Teramo, in Italy, reviewed clinical records of mares with a history of problematic behavior that had one or both ovaries removed. Researchers followed up with the mare owners and found they reported improvement in the horses’ behavior. Researchers noted histological exams later revealed granulosa cell tumors (GCTs) or granulosa teca cell tumors (GTCTs) on most of the removed ovaries.

Complaints from the mares’ owners had involved behavior problems during riding.

“They really don’t appreciate when you just try to ride them,” says Giulia Guerri, DVM, PhD, a specialist in equine medicine and surgery, resident ECVDI (European College of Veterinary Diagnostic Imaging), and a researcher in the Equine Medicine and Surgery Section at the University of Teramo.

Guerri was one of the authors of the study who cited “increased sensitivity at both flanks, general problems when ridden, and unwillingness to engage the hindquarters when ridden” as just a few of the problems common to the mares that had ovaries surgically removed.

When the veterinarians found tumors, “common behaviors were also biting or kicking other horses, kicking humans, bucking at work, pulling away from contact when asked to engage the hindquarters, and unwillingness to engage.”

Keep in mind that affected ovaries can become quite large. Normal ovaries are only a couple of inches in length, but a tumor can make them the size of a soccer ball or bigger.

“You can imagine that it’s also a problem during the riding,” Guerri explains. At that size, the ovaries pose a mechanical issue. “After the removal, you see really quick improvement (in) the behavior.”

Tumors can also disrupt hormones.

“The tumor involves specific cells of the ovary that are hormonally active,” Guerri says. “These cells can overproduce hormones (usually inhibin, testosterone, and anti-Müllerian hormone) leading to hormonal imbalances that cause ‘misbehavior.’ ”

In the case series study Guerri and her co-authors wrote, “The best option to diagnose GCT/GTCTs before surgical removal is a hormonal assay to measure the blood concentration of anti-Müllerian hormone. This is secreted by the granulosa cells in the ovary and has recently gained popularity as a potential biomarker for GCT/GTCTs.”

In an Equine Veterinary Journal study², University of California, Davis, researchers reported they were less likely to attribute bad mareish behavior to hormone problems: “Of the abnormal behaviors, stallionlike behavior was the only one that was found to have significant association with increased concentrations of the tested hormones,” the authors wrote.

UTIs and Kidney Infections

Urinary tract and bladder infections in mares can lead to frequent urination, posturing, and perineal irritation, often mistaken for estrous behaviors. Veterinarians typically examine and then treat affected mares with antibiotics to resolve these infections. 

Ridden Mares vs. Broodmares

Riding or exercising your mare can provide additional opportunities to detect that something’s bothering her. Grooming, tacking up, or riding all potentially involve touching the mare’s flanks. As Guerri points out, that pressure might be unpleasant.

Sport horse mares are common in these studies of estrus, ovaries, hormones, and how they impact mare behavior, she says. Returning a mare to productive under-saddle work is a frequent concern.

For owners of broodmares that exhibit problem behavior, there is hope; in the case series articles the authors reported that mares with just one ovary removed were able to get pregnant.

If you’re no longer riding your mare—whether she’s retired to pasture-puff status or is a broodmare—you’ll have to rely on other methods to detect unusual estrous behavior.

Entering estrus in the winter months would be one clue, Hitzler points out. You can also keep an eye out for how she behaves around geldings. Consider shifting turnout arrangements if your mare is sometimes receptive to geldings on a shared fence line. Horses could get hurt when a mare is considerably less enthused about a male horse’s attentions.

“You have to understand behavior,” Hitzler explains. “You have to understand whether this behavior is going to be dangerous for the horse.”

Reading ear, head, neck, and tail expression can help identify problems, she adds.

Other approaches, such as keeping track of food consumption, body condition score, and herd dynamics, might also provide insight.

Your Mare is Unique      

Mares are individuals. Some are spicy by nature while others are personable and sweet. Familiarize yourself with your mare’s habits and demeanor.

Hitzler recommends watching your mare’s facial expressions for clues about her mood or health.

So many people look at horses’ legs, shoulders, and feet while working with them on the ground.

“Look at their faces,” Hitzler urges. “Their faces tell you an awful lot, whether they’re content, whether they’re worried, whether they’re afraid. And then that also coordinates with the ears and neck height and body posture and tail. So, they all go together. But I think a lot of people forget that there’s a lot of facial expressions that go on with horses.”

Take-Home Message

If your mare is acting sour, there might be a health-related reason. Normal estrous behaviors include receptivity to a stallion, frequent urination, raising the tail, and winking the vulva. When estrous signs include sensitivity on the flanks, poor behavior under saddle, tail swishing, and squealing, you might consider chatting with your veterinarian.

References

1. Straticò. P.; Hattab, J.; Guerri, G.; Carluccio, A.; Bandera, L.; Celani, G.; Marruchella, G.; Varasano, V.; Petrizzi, L. Behavioral Disorders in Mares with Ovarian Disorders, Outcome after Laparoscopic Ovariectomy: A Case Series. Vet Sci. 2023 Jul 25;10(8):483. doi: 10.3390/vetsci10080483. PMID: 37624270; PMCID: PMC10458155.

2. Huggins, L. Norris, J. Conley, A. Dini, P. Abnormal mare behaviour is rarely associated with changes in hormonal markers of granulosa cell tumours: A retrospective study. Equine Vet J. 2023. doi.org/10.1111/evj.13967.

On May 1, a gelding at a private facility in Orange County, Florida, tested positive for strangles. The horse developed clinical signs on April 23, including nasal discharge and fever. He is under official quarantine.

This is Florida’s 17^th confirmed strangles case in 2025. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On April 23, a weanling colt in Ingham County, Michigan, tested positive for strangles after developing a fever and nasal discharge. He is under voluntary quarantine. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

About Strangles

Strangles in horses is an infection caused by Streptococcus equi subspecies equi and spread through direct contact with other equids or contaminated surfaces. Horses that aren’t showing clinical signs can harbor and spread the bacteria, and recovered horses remain contagious for at least six weeks, with the potential to cause outbreaks long-term.

Infected horses can exhibit a variety of clinical signs:

• Fever
• Swollen and/or abscessed lymph nodes
• Nasal discharge
• Coughing or wheezing
• Muscle swelling
• Difficulty swallowing

Veterinarians diagnose horses using polymerase chain reaction (PCR) testing with either a nasal swab, wash, or an abscess sample, and they treat most cases based on clinical signs, implementing antibiotics for severe cases. Overuse of antibiotics can prevent an infected horse from developing immunity. Most horses make a full recovery in three to four weeks.

A vaccine is available but not always effective. Biosecurity measures of quarantining new horses at a facility and maintaining high standards of hygiene and disinfecting surfaces can help lower the risk of outbreak or contain one when it occurs.

On April 22, a 16-year-old Quarter Horse mare at a boarding facility in Washington County, Minnesota, tested positive for equine herpesvirus-1 (EHV-1). The mare developed clinical signs on April 22, including ataxia and urine dribbling. She is under quarantine, and 30 horses are potentially exposed. 

EDCC Health Watch is an Equine Network marketing program that utilizes information from the Equine Disease Communication Center (EDCC) to create and disseminate verified equine disease reports. The EDCC is an independent nonprofit organization that is supported by industry donations in order to provide open access to infectious disease information.

EHV 101

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM.

In many horses, the first or only sign of EHV-1 infection is fever, which can go undetected. In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with EHM usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Herpesvirus is easily spread by nose-to-nose or close contact with an infectious horse; sharing contaminated equipment including bits, buckets, and towels; or clothing, hands, or equipment of people who have recently had contact with an infectious horse. Routine biosecurity measures, including hygiene and basic cleaning and disinfection practices, should be in place at all times to help prevent disease spread.

Current EHV-1 vaccines might reduce viral shedding but are not protective against the neurologic form of the disease. Implementing routine biosecurity practices is the best way to minimize viral spread, and the best method of disease control is disease prevention.

Although hyperflexion remains common in horse sports, an equine researcher focused on animal husbandry, behavior, and welfare recently emphasized that scientific consensus correlates riding horses behind the vertical to poor health and welfare. Researchers have found that hyperflexion—when the plane of the horse’s nose falls behind a vertical line—creates physical and mental stress, likely due to musculoskeletal pain, excessive rein tension, hindered eyesight, and possible airway obstruction, said Uta König von Borstel, PhD, a researcher at the University of Giessen, in Germany.      

“Our study (a literature review) very clearly shows that hyperflexion is bad for horse welfare, no matter what the circumstances are—full stop,” said König von Borstel, speaking at the 2025 Horse XP Experience for Wellness Conference, held March 15-16, in San Marcello Piteglio, Italy. 

The History of Hyperflexion in Horse Sports

Equestrians likely have been riding their horses behind the vertical for hundreds of years—as suggested by artistic drawings in early horsemanship books such as William Cavendish’s Méthode et Invention Nouvelle de Dresser les Chevaux (1658), as well as in paintings and statues of knights and noblemen across several centuries, she said. However, none of the writing in these early texts suggested people should work their horses in hyperflexion.

In competitive dressage hyperflexion became increasingly popular starting in the 1970s, and even more so in the 1990s, in a trend that continues to increase, said König von Borstel.

Officially, the Fédération Equestre Internationale (FEI) suggests dressage judges should prefer horses that keep their nasal plane at or in front of the vertical line. The current rules also place a strong emphasis on constant bit contact, she said. This might lead riders to never release tension—a practice that goes against the principles of ethical horse training “since there’s no striving for lightness,” König von Borstel says.

Studying the Effects of Hyperflexion on Horse Health

Because the topic has led to significant debate—with proponents claiming hyperflexion can improve horses’ range of motion and performance—König von Borstel investigated the body of research on the topic. To do so she teamed up with Andrew McLean, PhD, BSc, Dipl. Ed, founder of the Australian Equine Behaviour Centre, in Victoria, Australia; Kathrin Kienapfel, PhD, of the Swiss National Stud Farm’s Equine Research Group, in Avenches, Switzerland; Christina Wilkins, PhD candidate at the University of New England in Armidale, Australia; and Paul McGreevy, BVSc, PhD, MRCVS, MACVS (animal welfare), professor of animal behavior and animal welfare science at the University of Sydney, in Australia.

Together the researchers searched through all scientific papers published on hyperflexion—which they defined as any head position of any degree behind the vertical. They then selected 58 studies that met their criteria for reliability and robustness.

They found the studies showed negative effects of hyperflexion, such as stress and discomfort related to a forced position and the increased use of rider aids. The researchers had quantified these effects using measurable parameters including increases in heart rate, cortisol (the stress hormone) levels, and conflict behaviors.

Some researchers also reported airway restriction, “which is obviously a condition of serious discomfort for the horse,” König von Borstel said. Some scientists showed hyperflexion limited the horses’ forward vision, which can increase the animals’ anxiety and fear because they cannot clearly see in the direction they’re moving.

Researchers on multiple studies also indicated horses experienced negative results regardless of how long they were held in hyperflexion. “Even short periods in which the horse holds its nose behind the vertical can have negative consequences on its well-being,” König von Borstel said. Likewise, experience didn’t make hyperflexion any more tolerable, she added. “Horses well-accustomed to hyperflexion showed signs of discomfort.”

Even so, in 22% of the studies researchers reported insignificant results or concluded horse welfare had not been compromised, she said. In one study the researchers even suggested positive effects such as reduced stress as measured by heart rate variability after training. However, Koenig von Borstel said this particular study had confounding factors that could make its results less reliable.

Studying Hyperflexion in Equestrian Competition

Researchers on studies included in the review reported that hyperflexion led to better scores at international dressage events, whereas they associated it with poorer scores at low-level shows, said König von Borstel. This has been a progressive trend, she added, with hyperflexion present in 71% of dressage horses in 2008 compared to 45% in 1991 (researchers on one 2022 study included in the review suggested 96.8% of horses are ridden in hyperflexion at some point during international dressage competitions).

On the other hand, at advanced national levels the researchers saw no significant effects of hyperflexion on scores.

In breeding competitions young stallions ridden in hyperflexion received better rideability marks. However, König von Borstel noted the reason was unclear—judges might have viewed them as more obedient, or the horses might have been naturally flexible and adopted position on their own.

Take-Home Message

König von Borstel said the new literature review highlights negative welfare consequences of hyperflexion, including stress, musculoskeletal pain, and hindered vision or respiration, regardless of how hyperflexed the horse is. Although researchers on the reviewed studies did not directly investigate different degrees of hyperflexion, she noted that more pronounced hyperflexion could lead to greater impacts on horse welfare.

The study König von Borstel presented, “Hyperflexing the horse’s neck: a systematic review and meta-analysis,” appeared in Scientific Reports in October 2024.