CVM Researcher Discovers Domestic Horse Breed Has Third-Lowest Genetic Diversity

Story by Margaret Preigh

Dr. Gus Cothran
Dr. Gus Cothran

A recent study by Dr. Gus Cothran, professor emeritus at the Texas A&M School of Veterinary Medicine & Biomedical Sciences (CVM), has found that the Cleveland Bay (CB) horse breed has the third-lowest genetic variation level of domestic horses, ranking above only the notoriously inbred Friesian and Clydesdale breeds. This lack of genetic diversity puts the breed at risk for a variety of health conditions.

Genetic variation refers to the differences between different individuals’ DNA codes. Populations where there is high genetic diversity will have a wider range of different traits and will be more stable, in part because disease traits will be more diluted. In populations with low genetic variation, many individuals will have the same traits and will be more vulnerable to disease.

The CB is the United Kingdom’s oldest established horse breed and the only native warm-blood horse in the region. Used for recreational riding, driving, and equestrian competition, the CB is considered a critically endangered breed by the Livestock Conservancy.

Because maintaining genetic diversity within the breed is important to securing the horses’ future, Cothran and his team worked to gain comprehensive genetic information about the breed to develop more effective conservation and breeding strategies.

In this study, published in Diversity, researchers genotyped hair from 90 different CB horses and analyzed their data for certain genetic markers. These samples were then compared to each other, as well as to samples from other horse breeds to establish the genetic diversity within the breed and between other breeds.

Both the heterozygosity and mean allele number for the breed were below average, indicating lower than average genetic diversity within the breed. This low genetic diversity should be seen as a red flag for possible health conditions.

“Low diversity is a marker for inbreeding, which can cause low fertility or any number of hereditary diseases or deformities,” Cothran said. “With overall population numbers for the breed being so small, such problems could rapidly lead to the extinction of the breed.”

The Cleveland Bay Horse Society of North America estimates that only around 900 CB purebreds exist globally. Such low population numbers mean the breed is considered to be critically rare.

Cleveland Bay horses pulling a carriage
Cleveland Bay horses

This study also evaluated the diversity between the CB and other breeds using a majority-rule consensus tree, a type of analysis that shows an estimate of how different clades, or groups of organisms sharing a common ancestor, might fit together on their ancestral tree.

Cothran and his team’s analysis found that the CB did not show a strong relationship with any other breeds, including other breeds within the same clade. Though this could be a result of the low genetic diversity within the breed, these data suggest that the CB is genetically unique from other breeds. These findings place emphasis on the importance of CB horses as a genetic resource.

“The CB is an unusual horse in that it is a fairly large sized horse but it is built like a riding horse rather than a draft horse,” Cothran said, noting the uniqueness of the breed. “It frequently is bred to other breeds such as the Thoroughbred to create eventing or jumping horses, although this is a potential threat to maintaining diversity in the CB.”

Cothran hopes his research will help to inform conservation efforts supporting the longevity of the CB breed, as well as inform breeders on how they can more responsibly further their horses’ genetic lines.

“If any evidence of inbreeding is observed, breeders should report it to scientists for further analysis,” Cothran said. “Efforts should be made to keep the numbers of CB horses as high as possible and to monitor breeding practices to minimize inbreeding and loss of variability.”

“Domestic animals, including horses, are also at risk of declining populations, just like endangered species, but research can help determine which populations (breeds) are at risk and provide possible directions to help reduce risks or consequences,” he said.

Though CB horses are currently at risk, Cothran remains optimistic that careful monitoring and management of the breed can preserve them as a cultural and genetic resource for years to come.


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The Rundown on Equine Shoulder Sweeney

Horses are remarkably active animals that make good use of their limbs and joints as they canter, gallop, and trot. As such, it is important that owners are cognizant of their horse’s health and of potential conditions that might arise.

Three horses in a fieldDr. Jeffrey Watkins, a professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences, weighs in on shoulder Sweeney, also known as suprascapular neuropathy, a condition affecting the nerves and muscles of a horse’s shoulder region.

“Shoulder Sweeney refers to an injury of the suprascapular nerve, which runs over the front part of the scapula and provides the nerve supply to two major muscles that support the shoulder joint,” Watkins said. “When the nerve is injured, these muscles are unable to function normally and will undergo atrophy, which can occur very rapidly.”

This condition presents in two forms, chronic and acute, according to Watkins.

The chronic form of shoulder Sweeney was once common in horses that often pulled heavy loads, such as wagons and farm equipment, and was attributed to repetitive nerve injury often associated with ill-fitting harness collars.

In these chronic cases, clinicians typically find significant atrophy of the two major muscles that are supplied by the nerve overlying the scapula, and when these muscles atrophy, the bony spine of the scapula becomes very prominent.

Chronic shoulder Sweeney has become less frequent, as workhorses are less common.

“What we see today, most of the time, is a much more acute injury,” he said. “Usually, it’s because the horse is running fast and hits something immovable, another horse or a fence post, very forcefully with the point of their shoulder.”

This impact causes an acute nerve injury that results in dysfunction of the two major muscles noted above.  These muscles are responsible for maintaining the lateral stability of the shoulder joint and when they lose their nerve supply acutely, the shoulder region becomes unstable.

Watkins said it is important to consider other potential conditions that can occur secondary to a high-impact injury to the shoulder region. An examination by a veterinarian, including high-quality radiographs of the shoulder region, is necessary to rule out other injuries, such as a fracture.

Shoulder Sweeney is usually diagnosed by observing the gait of the horse and tends to be straightforward.

“They have a very characteristic gait where whenever they try to put weight on their leg, their shoulder joint partially dislocates to the outside,” Watkins said. “These horses don’t walk well; they have a very obvious gait abnormality that basically makes them unusable in the short-term.”

Though this condition can significantly impact a horse’s function in the short term, the good news is that most horses suffering from an acute shoulder Sweeney will recover stability in that joint over time and will be able to function normally again. But the process requires rest and patience.

“It’s important to recognize it can take quite a long time for that nerve to heal and to basically regrow,” Watkins said. “We usually say it will take six to eight months for that nerve to begin to regain function and for that shoulder to stabilize and no longer have issues.”

Although most horses recover their ability to move normally, atrophy of the muscles overlying the shoulder blade will usually be permanent and the horse will have the characteristic boney protrusion of the shoulder area associated with shoulder Sweeney for the remainder of its life.

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What to Know About Equine Osteoarthritis

Osteoarthritis is a progressive disease that compromises the joint health and mobility of many animals. While osteoarthritis is the most common joint disorder for people in the United States, the condition is also prevalent in horses.

Dr. Jeffrey Watkins, a professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences, provides insight into equine osteoarthritis and how owners might manage this condition in their horses.

“Osteoarthritis refers to deterioration of a joint or joints that is characterized by progressive loss of cartilage,” Watkins said. “The inflammation associated with osteoarthritis causes pain and swelling of the affected joints.”

Cases of osteoarthritis can be divided into two groups: primary and secondary.

Primary osteoarthritis arises from the wear and tear of everyday activities, resulting in a slow breakdown of joint cartilage. Performance horses are at particular risk for this form of osteoarthritis.

“Often, the first indication of a problem is a change in the horse’s behavior, willingness to perform, and/or ability to perform at their expected level,” Watkins said. “These are often subtle indications of a developing joint problem and are due to the low-grade pain associated with the insidious onset of osteoarthritis.”

Secondary osteoarthritis comes when an injury to a joint is severe enough to begin the process of cartilage breakdown. Horses with a history of joint infections, fractures involving the joint, ligament and tendon injuries, and preexisting joint defects are at risk for secondary osteoarthritis.

“Osteoarthritis secondary to an injury or infection will be characterized initially by the signs associated with the inciting injury. Once the initial injury has been resolved, osteoarthritis is manifested as continued loss of function due to pain and stiffness of the affected joint,” Watkins said.

If an owner suspects that their horse might be suffering from osteoarthritis, they should contact their veterinarian, who might conduct a physical evaluation and lameness examination, as well as recommend diagnostic imaging such as radiography, ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI).

Prevention of equine osteoarthritis varies depending on the type. For secondary osteoarthritis, prompt and proper treatment of the initial joint injury is vital. Primary osteoarthritis is more complicated, involving many factors including proper hoof care, responsible training regimens, and the monitoring of any predisposing factors.

“Management of osteoarthritis is a multifaceted approach and includes modification of the affected horse’s activity level, attention to body weight and body condition, appropriate hoof care, medical therapy, and surgical therapy,” Watkins said.

As with all conditions, owners concerned for their horse’s health should consult with their veterinarians to establish an individualized management strategy. Luckily, research into osteoarthritis management is ongoing, so we might one day see options for complete rehabilitation.

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Hay is for Horses: Maintaining a Proper Equine Diet

Nutrition plays a large role in a horse’s energy level, performance, and overall health. There are many feed and treat options available for horses, but some are more important than others for a complete and healthy diet.Grey horse with grass sticking out of its mouth in front of forest

Dr. Leslie Easterwood, a clinical assistant professor of equine community practice at the Texas A&M College of Veterinary Medicine & Biomedical Sciences, shares her recommendations for a proper equine diet.

“Components of most horse diets are roughly divided into two sections: grain concentrate, either pelleted or whole grain, and roughage, such as hay or fresh grass,” Easterwood said.

She recommends feeding 1 percent of a horse’s body weight as concentrate and 1 to 2 percent as roughage, with adjustments made to suit the horse’s activity level and ideal weight. Proper amounts of high-quality grain and roughage are essential for adequate nutrition and fiber intake and can help avoid health issues like colic.

There are many options for delicious treats for horses, such as carrots, apples, and commercially made treats, but they should only be fed in small quantities.

As with any other pet, there are special considerations for owners when making changes to a horse’s diet.

“The most important factor when considering a diet change is to gradually change from one type of foodstuff to another, allowing the gastrointestinal tract to adjust to the new foodstuff or amount,” Easterwood said.

Horses also can benefit from eating several small meals each day, rather than a few large meals.

“Wild horses are designed to intake small meals throughout the day,” she said. “This keeps their gastrointestinal tracts active and healthy. Meal feeding is not what their systems were designed for, but it is the standard practice for horse owners.”

When assessing the effectiveness of an equine diet, horse owners should watch out for signs of both undernutrition and overnutrition. Luckily, Easterwood said it is usually easy to tell if a horse is gaining or losing weight.

“A poor, dull hair coat can also be an indicator of poor nutrition or parasite infestation,” she said.

Undernutrition, either from too few calories or a lack of certain nutrients, can have obvious consequences on a horse’s weight, energy, and overall health.

Similarly, overnutrition, which can refer to obesity or the excessive intake of specific nutrients, can stress a horse’s heart and lungs, increase disease risk, and cause greater lethargy, according to the American Association of Equine Practitioners.

An equine veterinarian can help you develop the best possible diet for your horse, tailored to its individual needs. A well-fed horse will be happier and healthier and will have more energy to spend time with its owner.

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Stop the Spread of Vesicular Stomatitis

Outbreaks of vesicular stomatitis (VS) occur in Texas every several years, but until this June, there were no reported cases since 2014. Because horses near Austin were recently diagnosed with this disease, horse and livestock owners in nearby areas should take precautions to keep their animals safe.Colt in field

VS is a highly-contagious zoonotic disease that causes blisters in the mouth, tongue, teat, or hooves; crusty sores around the muzzle or hooves; and excessive salivation in horses and livestock, according to Dr. Michelle Coleman, assistant professor of large animal internal medicine at the Texas A&M College of Veterinary Medicine & Biomedical Sciences.

While this viral disease can affect horses, cattle, sheep, goats, and other livestock, on rare occasions, the disease can spread to people and cause flu-like symptoms, though VS is not highly contagious to humans.

“The virus can be spread through direct contact with infected animals, through saliva that can contaminate the environment, or by blood-feeding insects,” Coleman said. “People handling sick animals should wear gloves.”

Luckily, most animals are able to recover from VS with proper treatment, which mainly involves supportive care as blisters and sores heal by ensuring that animals continue to eat, drink, and behave normally.

“Due to pain of the blisters around the mouth, horses may be reluctant to eat,” Coleman said.

While animals are being treated for VS, they should stay isolated from healthy animals to avoid spreading the disease. Owners should watch out for any new physical symptoms or behavioral changes and talk to a veterinarian if concerned.

Additionally, there are several preventative steps that livestock owners can take to keep VS from spreading to their animals.

“Strategies suggested for the prevention of this disease include control of biting insects and isolation of affected animals, which is essential to reduce the burden and spread of disease,” Coleman said.

“The Texas Animal Health Commission mandates a 14-day quarantine period from the onset of lesions in the last affected animal on any premises with suspected or confirmed VS cases,” she said.

Because of the recent VS outbreaks, it is especially important that livestock owners watch out for signs of the disease and contact a veterinarian if they suspect their animals may be ill.

If VS is caught early and treated persistently, infected animals can recover and go on to live healthy lives. If everyone does their part to prevent the spread of this disease, Texas can once again be free of vesicular stomatitis.

Pet Talk is a service of the College of Veterinary Medicine & Biomedical Sciences, Texas A&M University. Stories can be viewed on the web at Suggestions for future topics may be directed to

The Magic of Horses

Texas A&M’s Equine Therapy Program is changing the lives of veterans and people with disabilities.

Story by Jeannie Ralston, Spirit Magazine, Texas A&M Foundation


Student, Wyatt Branum and his father Jay Branum, and Dr. Nancy Krenek

The Courtney Cares program makes all the difference for 9-year-old Wyatt Branum (pictured to the right), who was born with Down Syndrome. In four years of riding, he’s made tremendous progress mentally and physically. While never reluctant to ride, he can now mount and dismount his horse Straw Flying Down, who happens to be a gift from Lyle Lovett ’79 to the Parsons Mounted Cavalry, with little assistance. He trots on the horse, centers himself when off balance in the saddle and listens with 100 percent attention to his instructors.


Courtney Grimshaw ’85 loved horses.

Growing up outside of Colorado Springs, she got her first horse in high school. When she was attending Texas A&M, she had an experience that sparked a dream for her: She helped a friend’s son, who had a debilitating disease, learn to ride. 

“The child’s mother said it was the first time he did anything other kids could do,” said Dee Grimshaw, Courtney’s mother. “It was so rewarding for her.” 

Seeing the change in the boy planted Courtney’s dream of someday having a horse camp for kids. 

“She thought a horse could cure everything,” Dee continued. “Really that was the bottom line.”

But the idea of a camp was sidelined as Courtney, who was an animal science major at Texas A&M and earned an MBA in accounting from The University of Texas, built an impressive career in international finance—much of it spent in Kazakhstan as the tax partner for the global region of PricewaterhouseCoopers. 

When she wasn’t negotiating business opportunities for the developing country, Courtney rode dressage horses, which she bought from a breeder in Poland. In 2010, after 12 years in Kazakhstan, she was preparing to return to Texas to live. 

She built a home on acreage near the small town of Thorndale—between Austin and College Station—and started erecting a state-of-the-art horse barn, which would have been ideal for that children’s horseback riding camp she’d planned. 

But, then, just months before leaving Kazakhstan, Courtney passed away unexpectedly at age 46, leaving her family and friends devastated.

“We felt a huge hole in our lives,” Dee said. “We had to do something for her, something to help people. That’s what she would do.” 

Collectively, the Grimshaw family sold her property in Thorndale and used the funds to establish an equine therapy program at Texas A&M. 

“We connected the dots and decided this would be an ideal way to honor her,” said Jim Grimshaw, Courtney’s younger brother. “This is our way of perpetuating her spirit and making something good come out of our terrible loss.”

Because Courtney was such a fervent Aggie, the family reached out to The Texas A&M University System.

“From the word ‘go’ all the pieces came together in a way that continues to surprise and delight us, especially since the program supports the values of Texas A&M—research, education, and service,” Jim said. “It seems like Courtney was guiding the process. Serendipity is the word that comes to mind when we talk about it. Things just seemed meant to be.”

Wyatt Branum and his father Jay Branum


Launched in 2012 with $1.2 million from the sale of Courtney’s property, Courtney Cares was designed to do more than help local children, adults, and veterans in need of services. It was designed as a living, breathing, educational laboratory and classroom where students interested in volunteering could learn about the benefits and needs of the Equine Assisted Activities and Therapy industry.

Courtney Cares is operated through a strategic partnership with the Corps of Cadets’ Parsons Mounted Cavalry and Dr. Nancy Krenek’s therapy center, Ride On Center for Kids (ROCK), which provides professional instructors, licensed therapists, and more than 20 years of experience. 

When Krenek was approached by the System in 2012 to head up this project, she knew that Texas A&M could be the catalyst for promoting excellence in this industry because of its high standards of service, education, and research.

Today, the program helps children, adults, and veterans experience the life-changing therapy of horses. 

Currently, 15 to 20 of the Cavalry’s 66 horses are part of the program, and each horse is vetted by the standards of the Professional Association of Therapeutic Horsemanship.

“Our horses work well because they’re trained to trust their riders and ground handlers to keep them safe,” said Bob Byrns ’74, the Cavalry site manager. “Once horses have accepted the leadership relationship, they will do almost anything to please their leader.”

Courtney Cares supports the Cavalry’s budget by helping to pay for horse maintenance, renting Freeman Arena, and buying equipment such as saddles, helmets, and horse trailers. Texas A&M students—often from the health sciences, education, and animal science fields—serve as volunteer side walkers and horse handlers during Courtney Cares sessions.

Two types of sessions are offered at no charge for a couple hundred participants. The first is for children and adults with challenges that are either physical or emotional. The second is for veterans who are seeking to learn leadership through horsemanship as they adjust to their post-military life, often with physical injury or PTSD from their service. 

“The movement of the horse provides a deep-pressure stimulus with each step,” explained Krenek. “The rider can receive 160 to 200 biofeedback impulses per minute in the neuromuscular system, the brain, the nerves, and the muscles. These impulses provide a calming effect on the nervous system that helps participants respond in a more proactive way to life. The cause-and-effect relationship with the horse also allows self-discovery and opportunities for leadership that aid in teaching horsemanship, appropriate behavior, and social skills.”

Courtney’s brother, Jim Grimshaw (right), contacted The Texas A&M University System about the possibility of establishing an equine therapy program in her honor. The program began in the fall of 2012, funded by a generous donation from Jim and his parents, Dee and his late father, Bo (center).

Equine Assisted Activities and Therapy is a growing field because of many studies that have demonstrated the ways horses help people improve physically and emotionally. “There are multifaceted opportunities for improvement,” said Dr. Jim Heird, executive director of the Equine Initiative at Texas A&M, a joint program between the College of Agriculture and Life Sciences and the College of Veterinary Medicine & Biomedical Sciences (CVM). “We know that the movement of the horse closely duplicates the movement of human walking. People can improve their core muscles and walking by riding a horse.”

As for emotional benefits, Dr. Priscilla Lightsey ’80, a physical therapist with Courtney Cares who is also a hippotherapy clinical specialist, explained one reason horses have such an impact.

“Participants have to communicate with the horse,” she said. “They have ownership and control of something 1,200 pounds. That’s powerful.”

“Horses are always looking for a leader,” added Heird.

This, he noted, helps children and those with disabilities gain confidence as they guide the animals. For veterans, taking care of a horse can make them feel whole.

“Veterans do the same tasks the cadets do for the horses, but at a slower pace,” Byrns said. “They have to modify their behavior to work with horses; they have to be calm and gentle. It really helps them handle their personal relationships with their kids and spouses better.” 

A research study that included the Courtney Cares program documented a 74 percent decrease in PTSD symptoms and an 86.8 percent improvement in veterans’ overall mental health.

The fact that Courtney Cares would benefit military veterans made the Grimshaw family even more comfortable with the goals of the program. 

Courtney’s father, the late James A. “Bo” Grimshaw, Ph.D., was a retired Texas A&M Regents Professor for Life and Texas A&M Commerce Professor Emeritus, as well as a retired Air Force lieutenant colonel. “It is powerful to see the list of outcomes for participants in the program, and that means a great deal to our family,” Bo said before he passed away in April 2018. “Courtney continues to have a positive effect on so many people. That is the legacy our family wants to perpetuate.”


Note: This story originally appeared in the 2019 Spring edition of CVM Today. This is a condensed version of The Magic of Horses. The original version was published in the Texas A&M Foundation’s Spirit magazine. You can read the full story at

For more information about the Texas A&M College of Veterinary Medicine & Biomedical Sciences, please visit our website at or join us on Facebook, Instagram, and Twitter.

Contact Information: Jennifer Gauntt, Interim Director of Communications, Media & Public Relations, Texas A&M College of Veterinary Medicine & Biomedical Science;; 979-862-4216

Equine Dental Health: Straight From the Horse’s Mouth

Dr. Leslie Easterwood looking at horse's teethHorses use their teeth for several functions, including eating, grooming, and defense. Like most other pets, horses need regular check-ups and maintenance for their teeth, which should be done by an equine veterinarian.

For National Pet Dental Health Month this February, Dr. Leslie Easterwood, a clinical assistant professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences, has advice for keeping a horse’s teeth clean and healthy.

Easterwood said the most common dental issue for horses is the development of sharp enamel points that form naturally when horses grind their teeth.

“Horses develop sharp enamel points along the cheek side of their upper cheek teeth and along the tongue side of their lower cheek teeth,” she said. “These sharp enamel points can cause ulcerations down the insides of their cheeks and along the sides of their tongues.”

Easterwood said these ulcers can be very painful, especially when a bit is used for riding. As a result, the horse may be resistant to riding or otherwise not behave normally.

There are many signs horse owners can look for that indicate their horse is having dental issues. According to Easterwood, these include drooling, dropping grain, refusing to eat long-stem roughage, performance issues, and turning the head to the side when eating.

The sharp enamel points can be reduced by an equine veterinarian through a procedure called dental floating, which involves smoothing down the edges with a dental file.

“Horses should have their first dental floating prior to putting the bit in their mouth for the first time,” Easterwood said. “After that, most horses should have their teeth floated once a year.”

She added that the teeth may need to be examined at least twice a year if they are wearing abnormally. A dental check should also be performed anytime the horse is eating strangely or reacting to the bit.

Equine veterinarians may also perform other dental procedures, such as addressing soft tissue problems in the mouth and pulling teeth.

“Loose or broken teeth, along with retained baby teeth, may need to be removed. Older horses can have other developmental issues that also require removing teeth,” Easterwood said.

If your horse is showing any of the signs of dental pain or has not had a dental checkup in a while, make sure to contact your veterinarian. Your horse will be happier with a mouth full of clean, healthy teeth.

Pet Talk is a service of the Texas A&M College of Veterinary Medicine & Biomedical Sciences. Stories can be viewed on the web at Suggestions for future topics may be directed to

Routine vaccinations are essential for equine health

Two horsesVaccines are one of the easiest and most efficient ways to protect your horse’s health, preventing the contraction and spread of infectious diseases including Rabies, West Nile Virus, and Influenza.

In continuation of National Immunization Awareness Month, Dr. Leslie Easterwood, a clinical assistant professor at the College of Veterinary Medicine & Biomedical Sciences, offers recommendations for equine vaccinations, suggesting that horses begin a routine vaccination schedule at a young age.

“We typically start foal vaccinations at 90 days of age,” Easterwood said. “If the mare is currently vaccinated and boosted late in her pregnancy, she will provide temporary immunity to the foal until they are able to respond to vaccinations. If the mare was not boosted late in pregnancy, we may choose to start vaccinations at 60 days.”

Depending on their location and proximity to disease, horses should receive vaccines for a number of harmful and potentially life-threatening illnesses.

“In Texas, the routine vaccinations for horses are Rabies, Venezuelan equine encephalitis (VEE), Eastern equine encephalitis (EEE), Western equine encephalitis (WEE), West Nile Virus, Influenza, Rhinopneumonitis type 4, and Strangles,” Easterwood said.

Rabies, VEE, EEE, WEE, and West Nile Virus cause neurological conditions in horses, while Influenza, Rhinopneumonitis type 4, and Strangles cause respiratory infections. Vaccines that are not commonly administered in Texas—because the likelihood of contracting the disease is low— include Potomac horse fever and botulism vaccines, according to Easterwood.

“Because of the differences in risk, what is recommended for one group of horses may not be best for all groups,” she said. “A possible vaccination schedule could be rabies once a year and the other recommended vaccinations twice a year. A consultation with your veterinarian to discuss the risk of exposure for your horse, based on activity and travel schedule, will allow them to develop a recommendation for vaccination schedules.”

Easterwood said she believes the risk of contracting disease significantly outweighs the minimal amount of risk associated with vaccinations. As always, if any serious or unusual side effects are noted, owners should contact their veterinarian immediately.

“Horses may become sore at the injection site, similarly to how people get sore after a vaccination,” she said. “Usually minor reactions are controlled with anti-inflammatories and a little time.”

The most important resource for questions or concerns regarding vaccinations will always be your veterinarian. By planning ahead, establishing a vaccination schedule, and maintaining a relationship with a veterinarian, owners can ensure their horse stays happy and disease free.

Pet Talk is a service of the Texas A&M College of Veterinary Medicine & Biomedical Sciences. Stories can be viewed on the web. Suggestions for future topics may be directed to

Horses with Heart


Texas A&M Stock Horse Team
Horses on the Texas A&M Stock Horse Team are being studied by CVM clinicians.

“That horse has a lot of heart.

There is no better compliment to bestow on a ranch horse. Far more than descriptive of its endurance and athleticism, the statement defines a horse’s physical and mental toughness and willingness to try, despite being maximally challenged or physically exhausted.

These guys want to give their all, regardless of their job description. No quit. No counterfeit.

In order to “give his all,” the horse must call upon mental and physical attributes, of his heart; intestinal fortitude, plus the efficient 8- to 10-pound muscular pump. Secretariat’s heart was estimated to weigh 20 pounds.

The equine heart must circulate about 12 gallons of blood per minute through its 1,200 pound body while performing with speed, agility, and endurance. Adding excitement to the equation generates an appreciation that horses need to be “heart healthy” to benefit their own, as well as their riders’, safety.

But as tough as horses are, their equine cardiac pumps occasionally malfunction due to heart diseases. Additionally, cardiovascular problems may be responsible for poor performance.

Fortunately, significant heart disease is rare.

However, in elite equine performance athletes, such as racehorses or any horse that works at high speeds, it is considered the third most common reason for poor performance, after lameness and respiratory diseases.

So it’s important for horsemen to recognize symptoms of equine acute and chronic heart disease. Awareness of other syndromes predisposing horses to heart problems is key.

Heart attacks similar to those suffered by humans, such as coronary artery disease, are extremely rare in horses, as are strokes and other peripheral artery diseases. Because of their unique athleticism, horses can compensate for diseased hearts for many months or years without signs of heart failure. However, eventually these heart muscles may weaken, losing ability to provide adequate circulation in meeting the body’s needs.

Large vessel ruptures are very rare but can lead to collapse or sudden death, usually when the horse is exercising. Internal parasite-induced aneurysms can be prevented by proper de-worming practices.

Traumatic injuries are uncommon, but deep, penetrating wounds to the chest cavity can be fatal, depending on the extent and location; branches, pipe, fenceposts, horns, etc., can be culprits. Accidents, unfortunately, come with athleticism and environment.

Horses can develop heart diseases quickly or over a period of time. The most common congenital disorder of horses is Ventricular Septal Defect (VSD). Foals are born with a hole in the wall separating the two lower chambers of the heart. Symptoms include lethargy, shortness of breath, and the inability to exercise normally. VSDs are associated with loud heart murmurs.

Developmental heart diseases in horses most commonly involve valves. As valve leaflets thicken, becoming deformed, usually with age, leaks can develop, leading to fluid accumulation and cardiac insufficiency. Clinical findings in severe disease can include murmurs, jugular vein distention, cough, and fluid accumulation in the abdomen, legs, or underbelly.

Common toxins affecting equine cardiac function include Monensin and Lasalocid (livestock feed additives and supplements), blister beetles in alfalfa hay, plus ornamental landscape plants, including oleander, rhododendrons, and yew. Certain wildflowers—such as potentially cardiotoxic milkweeds—are generally unpalatable to horses, but inadvertent ingestion comes from clippings or contamination of hay. Rattlesnake venom can have cardiotoxins that damage equine heart muscle, a syndrome that may be underdiagnosed, depending on where the horses live.

Horses have more abnormal heart rhythms than any other domestic animal species. However, not all are considered to cause horses problems. Atrial fibrillation (AF) is the most common clinically relevant arrhythmia in horses; the atria fail to contract but instead quiver or fibrillate. Upper heart chambers may beat up to 400 times per minute, going to non-stop; this rapid fluttering action doesn’t produce significant blood circulation into the lower chambers, thereby negatively affecting performance.

AF is often associated with poor performance in horses practicing high-intensity exercise. It’s also the most common cardiac arrhythmia in human athletes engaging in endurance sports. AF often develops in horses with advanced heart disease; AF can develop with minimal or no detectable cardiac signs. Electrolyte abnormalities, resulting from excessive sweating, may predispose horses to AF. It can also occur in horses having experienced previous illness that inflames the heart muscle (such as severe colic, influenza, and toxemia).

In addition to clinical signs, thorough auscultation of the heart alerts veterinarians about cardiovascular disease when murmurs and abnormal rhythms are heard. The next tool for the evaluation of horses with murmurs or arrhythmias is centered on the echocardiogram. This diagnostic modality is becoming increasingly available at many referral equine hospitals.

Aiding the assessment of athletic performance in equine sports, Standardized Exercise Testing (SET) can be useful to evaluate poor performance, the assessment of training progression, and as preventative medicine tools.

In order to utilize SET in western performance horses clinicians at the Texas A&M University College of Veterinary Medicine & Biomedical Sciences (CVM) are validating a protocol for exercise testing. Horses in this study are competitors on the Texas A&M Intercollegiate Stock Horse Team and had met show season expectations.

“Clinicians are hoping this protocol will be useful for investigating poor performance and as a preventative medicine approach of the management of high-level western performance horse athletes,” said Dr. Cris Navas, a clinician and professor of equine internal medicine in the CVM’s Veterinary Medical Teaching Hospital (VMTH).

“This comprehensive exercise testing protocol simultaneously evaluates musculoskeletal, respiratory, and cardiovascular systems and was assessed by historical questionnaires, general physical, and subjective lameness examinations and gait analysis using digital body mounted sensors,” he said. “Resting and dynamic upper airway endoscopy, plus evaluation of respiratory tract secretions were utilized. Echocardiograms, resting, and exercising electrocardiograms (ECGs), sweat responses testing, and laboratory values were acquired during the project. ”

Subclinical abnormalities were detected frequently in these horses—with the musculoskeletal system being the most commonly affected.

“But cardiovascular, plus upper and lower airway abnormalities, were also detected. These results suggest exercise tests may be useful to detect subclinical abnormalities in western performance horses,” Navas said. “Further evaluation of both normally and poorly performing horses is necessary to determine if exercise testing can improve health, performance, and welfare of these horses.

“For people with horses with poor performance, my recommendations are to have a veterinarian you are confident with examine the horse,” he said. “If there is a clear abnormality—like lameness, wheezes, coughing, heart murmurs—that can explain the performance problem, investigate or treat. If there is no smoking gun, do an exercise test that evaluates all body systems at the same time. This has two advantages: saving time, while diagnosing subclinical problems that can be treated simultaneously. The disadvantage is cost and sometimes inconvenience.”

The CVM believes each member of a team—which includes a primary-care veterinarian, trainer, and specialist in internal medicine, surgery, sports medicine, and rehabilitation—can solve part of the poor performance or preventative medicine equation.

“With the help of the Texas veterinary community, we hope to move forward with further clinical trials in sports medicine that also will hopefully prevent the rare events associated with equine activities or sports resulting in compromised (sudden death) safety of horse and rider and public perception of welfare during equestrian sports,“ Navas said.

“I should think that ranch horses should follow the same pattern as occurs in previous studies in sport horses, in that they often have several subclinical diseases simultaneously that don’t quite stop them from exercising,” Navas said. “Lameness is consistently the most common one in other groups, then respiratory, second, depending on the group, then cardiac disease more rarely.”

Ranchers and cowhands may not label their “toppy” horses as “elite equine athletes,” but when athleticism (turning a cow), speed (getting around cattle fixin’ to scatter), agility (dropping off in a draw), and excitement (‘ringy’ cows, town, indoor arenas) are considered, ranch horses may be more “elite” than previously considered.

Food for thought, considering numbers of ranch horse sales (and average price tags) are increasing: “Sound, gentle, capable, athletic…with a BIG HEART“ are always good in sale catalogue resumes.


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Contact Information: Megan Palsa, Executive Director of Communications, Media & Public Relations, Texas A&M College of Veterinary Medicine & Biomedical Science;; 979-862-4216; 979-421-3121 (cell)

This article, written by Dr. Ginger Elliott, was previously published in Livestock Weekly. It appears in the Spring 2018 edition of CVM Today magazine.

Does your horse need extra care this winter?

two horses on the fieldTexas may have mild winters, but that doesn’t mean temperatures can’t drop below freezing. On these cold days, how can horses stay warm?

In general, horses’ coats are enough to keep them warm in the winter, even in snowy weather, said Leslie Easterwood, clinical assistant professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences. But for owners who clip their horse’s coat short during the winter, it is necessary to provide your horse with ways to stay warm.

One way to help your horse stay warm is by providing shelter. A closed-in barn is nice, but not required, Easterwood said. Generally, as long as the horse has some way of escaping the weather, their coats should be adequate in maintaining body heat.

“Horses generally grow enough hair to stay warm,” Easterwood said. “The worst weather for them is when conditions are wet and windy. If they have a shelter to avoid the wind and rain, then they will be more comfortable.”

Another way to keep your horse warm is to provide a horse blanket. Blanketing is not a necessity for most horses in Texas, but blanketing is essential for horses with clipped coats. However, as the temperatures warm up throughout the day, the blanket will need to be changed to prevent sweating. A horse that sweats under their blanket may fall ill.

If keeping warm requires more calories, should you feed your horse a more calorie-dense diet in the winter?

It depends on the horse’s activity, according to Easterwood. Most horses’ normal diets are sufficient through the winter, but if you are regularly exercising your horse or the horse is underweight, you may consider increasing their caloric intake.

“Usually owners ride less in the winter, which could allow for energy to be diverted to keeping warm,” Easterwood said. “But if owners continue to ride during the winter, it could be necessary to provide more roughage for the horses.”

The winter months in Texas may not be as cold as other places, but horses with clipped coats may still find the weather to be too cold to bear. If you’re going to clip your horse’s coat during the winter, be sure to provide them with ways to stay warm.

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