Results of a four-year prospective study designed to determine the influence of training and heart size on atrioventricular (AV) valvular regurgitation (backflow of blood from the lower to the upper heart chambers) in Thoroughbred racehorses, and to determine any association between AV valve regurgitation and performance in Thoroughbreds, were presented by Lesley Young, BVSc, PhD, DVA, DipECVA, DVC, MRCVS, of the Animal Health Trust (AHT) in Newmarket, England, at the 43rd British Equine Veterinary Association Congress.

She said the causes of poor performance in racehorses include:

• Unreasonable owner expectations;


• Lack of genetic ability;


• Lack of enthusiasm;


• Orthopedic problems (most common);


• Respiratory disease (close second); and


• Cardiovascular dysfunction (consider after above causes).

“How important is cardiac disease to racehorse performance?” she asked the audience. “It’s believed to be the primary cause of, or a significant contributor to, poor or loss of performance in less than 6% of horses referred for performance investigation on the treadmill to AHT.”

While that seems like an insignificant number of horses affected, all equine veterinarians know that many racehorses have cardiac abnormalities, though in the majority of cases these abnormalities do not affect the horse’s performance