Heart Size and Racing Performance in Trotters

When it comes to the hearts of Standardbred racehorses, size does matter. Danish researchers recently published the results of an echocardiographic study in which they found that heart size correlated with athletic performance. However, "excellent cardiac function is only one of the important requirements to become a successful athletic horse," concluded the authors.

Heart size has long been believed as an indicator of talent in racehorses, and it has been shown that Thoroughbreds in training have hearts that are larger than untrained Thoroughbreds. The same is true in Standardbreds.

According to the Rikke Buhl, DVM, PhD, and other researchers at Denmark's Royal Veterinary and Agricultural University, human studies using echocardiography (a test that uses high-frequency sound waves to image the heart and surrounding tissues) have suggested that athletic training might be associated with an increase in the size of the left ventricle (the lower left chamber of the heart, which pumps oxygenated blood out to the body) secondary to increased wall thickness, increased chamber diameter, or both.

The study, which appeared in the Journal of the American Veterinary Medical Association, detailed the study of 132 trotters (76 females and 56 males). The horses were all untrained 2-year-olds when the study began. The veterinarians looked at each horse's heart four times at six-month intervals using echocardiography. They combined this information with data on training intensity and racing performance for the 103 horses that completed the study.

The researchers said that significant heart enlargement took place during the study period. There was a 12% increase in the left ventricular internal diameter in diastole (LVIDd, the internal diameter of the left ventricle as it fills up with blood to pump into the aorta, which takes blood to the rest of the body), a 40.3% in the estimated left ventricular muscle mass (LV mass), and in the mean wall thickness attributable to eccentric left ventricular hypertrophy (thickening of the ventricle with dilation, 11.6%). These changes are characteristic of endurance-trained athletes.

Estimated body weight was positively correlated with left ventricular size; malles had larger LVIDd and LV mass than females, and horses that were racing had larger LV mass than unraced horses, all findings which correlated with previous study results. The relationship between LV size and race performance was strongest at the time of the fourth examination when the horses were 3-year-olds.

While all 103 horses raced at least three times, only 63 were racing regularly by the end of their 3-year-old year, which the authors stated was a normal rate for trotters in Denmark.

The authors warned, "This study design was not able to define the extent to which normal physiological growth, training, management, and genetic effects separately influenced the degree of cardiac changes."

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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