Skip to content
Search Library
thumbnail

Abnormal sounds, known as murmurs, can sometimes be heard as a veterinarian listens to a horse’s heart. Owners who hear the words “heart murmur” may worry that their horses can’t be ridden or are in danger of dying. And would anyone buy a horse at a sale, knowing it had a heart murmur? Thankfully, though a heart murmur is not an uncommon finding on examination, the majority of horses are not troubled by this condition, and their sale prices and performance potential are often completely unaffected. However, some types of heart murmur signify serious problems, and a veterinarian will be able to determine how significant the condition is for a particular horse.

A number of studies have been conducted to evaluate cardiac abnormalities in the equine population. In Australia, researchers at the Department of Veterinary Clinical Sciences at the University of Sydney looked at 846 racing Thoroughbreds. They found that 686 of these horses (81%) had some type of heart murmur. The researchers concluded that most of the murmurs did not seem to be clinically important.

Another study was done in Italy by the Department of Veterinary Clinical Sciences, Equine Internal Medicine and Sports Medicine Services at the Large Animal Veterinary Hospital of the University of Milan. Researchers investigated the cardiovascular systems of 752 Standardbreds that had been presented for examination because of poor performance. In this group, 233 horses were found to have heart murmurs. Most of the murmurs were due to tricuspid valve regurgitation, but mitral valve, aortic valve and pulmonary valve-related murmurs were also identified. Though all of the Standardbreds had shown poor performance, their problems at the track could be traced to heart murmurs in fewer than one-third of the horses.

Researchers at Specialist Equine Cardiology Services in Suffolk, England, were interested in the possible association between murmurs and athletic performance, which was largely unknown.  They looked at 526 fit Thoroughbreds that were either jump or flat racing. After evaluating the horses and correlating their conditions to racing performance, the researchers found essentially no evidence that horses with murmurs performed any differently from those without murmurs.

At a recent FEI endurance competition held in Ashville, North Carolina, event veterinarians identified six horses with cardiac murmurs out of the nearly 200 starters. None of the competitors had problems with performance, and all finished the race normally.

When a murmur is found in a horse that is already performing satisfactorily, it might be expected to lower the value of the horse in the eyes of a prospective buyer. This was borne out in a study led by Dr. Marianne Sloet at the Department of Equine Sciences of the University of Utrecht in the Netherlands. During a five-year period, the study team looked at a number of horses for prepurchase examinations or at long distance rides. They found murmurs in 62 horses at prepurchase examinations and in 15 horses competing at distance rides. Mitral valve problems were found in 63 horses, and tricuspid valve issues were noted in 40 (some horses had multiple problems).

Reduced performance was found in only 10% of the horses that had heart murmurs, but the presence of murmurs nevertheless affected the sale price of many of the horses. Among the horses in the study, 43% sold for the original asking price, despite being identified as having a murmur; 21% sold for a lower price because of the presence of a murmur; and the sale was terminated in 36% of these cases. Clients apparently viewed the presence of heart murmurs as a detriment, even though less than 10% of horses with murmurs demonstrate any clinical significance.

The researchers found that the left atrial diameter (LAD) was the most important feature to predict future performance. When blood leaks into this chamber through a compromised mitral valve, the heart’s left atrium increases in size and the walls gradually thicken as the atrium works harder to push the blood out. If LAD is normal (less than 14 cm) in the presence of a heart murmur, then the flow problem is being well tolerated by the equine heart and shouldn’t cause performance concerns. If the LAD is increased, the heart is adapting to the pathology in the valves, and the horse should be removed from performance and carefully monitored.

X

Subscribe to Equinews and get the latest equine nutrition and health news delivered to your inbox. Sign up for free now!