Aortic Valve Prolapse Prevalence in Horses Determined by Type, Duration of Training, ACVIM 2009

Certain levels and durations of training may predispose horses to aortic valve prolapse (AVP), said Gayle Hallowell, MA, VetMB, CertVA, Dipl. ACVIM-LAIM (large animal internal medicine), MRCVS, who presented research findings at the American College of Veterinary Internal Medicine Forum, held June 3-6 in Montréal, Quebec.

To date, the prevalence of aortic valve prolapse in the horse has only been reported in a small group of racehorses, and scientists have not investigated risk factors for the condition.

According to Hallowell, aortic valve prolapse in horses is a condition in which the valve bows back into the left ventricle instead of snapping shut. The condition can only be diagnosed by ultrasound, and it does not pose any problems for the horse.

Researchers on the study evaluated groups of horses from different training levels and age ranges to assess prevalence of AVP. They performed echocardiography on foals, older unexercised horses, army horses undergoing moderate intensity exercise, racehorses, and National Hunt horses. Examinations were repeated every sixmonths to assess effects of age and training.

The research reflected that while age and sex had no effect on the prevalence of AVP, training did have an impact.

In the group of racehorses examined, AVP developed in 70% of the animals that did not previously have the condition. The group of army horses examined also reflected the effects of training, with 44% of the horses developing the condition.

During the study, researchers noted that applying a twitch appears to affect valvular function, as it induced AVP in 50% of the horses.

Researchers concluded that certain groups of horses are more prone to AVP. Also, the type and duration of training horses experience affects valvular dynamics, which, in turn, might determine prevalence of the condition.

"What is interesting about this condition is that it causes the valve to become leaky," said Hallowell. "What we are interested in following (over the next 10 years or so) is whether this condition predisposes these horses to developing significant disease of the aortic valve."

According to Hallowell, AVP might predispose horses to developing regurgitation later in life due to abnormal blood flow and change in hemodynamics.

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