Horses with Heart
Posted June 05, 2018
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
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
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
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
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
“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
“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
“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
“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
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
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.
This article, written by Dr. Ginger Elliott, was previously
published in Livestock Weekly. It appears in the Spring 2018 edition of CVM Today magazine.
Contact Information: Megan Palsa, Executive
Director of Communications, Media & Public Relations, Texas
A&M College of Veterinary Medicine & Biomedical Science; email@example.com;
979-862-4216; 979-421-3121 (cell)
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