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Horses with Heart

Posted June 05, 2018

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

Contact Information: Megan Palsa, Executive Director of Communications, Media & Public Relations, Texas A&M College of Veterinary Medicine & Biomedical Science; mpalsa@cvm.tamu.edu; 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.

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