Standardbred Racing Performance after OC Surgery Evaluated

The researchers found that hock OC lesions were more common in trotters than pacers (shown here), while lesion location within the joint tended to vary between the two groups.

Photo: Thinkstock

Standardbred yearlings that undergo surgical treatment for hock osteochondrosis (OC), a common form of developmental orthopedic disease, can be expected to perform as well as horses that do not suffer from the condition, researchers at the University of Minnesota and Rutgers University have concluded.

In their recent study, the team looked at the 2-year-old race performance records of 278 horses, 133 of which had hock OC lesions that were surgically removed prior their sale as yearlings. The other 145 horses were age-matched controls that were confirmed radiographically to be OC-free.

All the horses were born and raised on the same breeding farm before they went to yearling sales. “Because we know that there are important environmental or management-related risk factors for the development of OC, this gave us a more homogenous group to study,” said Annette McCoy, DVM, MS, PhD, Dipl. ACVS, of the Veterinary Population Medicine Department at the University of Minnesota.

“We also had a smaller group of 94 horses that we were able to follow through their 5-year-old racing season, so four consecutive race seasons," she continued. "Of those horses, 32 were surgically treated for hock OC as yearlings and 62 were unaffected age-matched controls.”

When considering both short and long-term performance, the results showed that horses that had OC lesions removed surgically performed similarly to their unaffected counterparts, said McCoy. “Globally, there were very few differences between the two groups.”

When looking at the OC-affected group specifically, however, the researchers found a couple of differences, she added: “One is that horses that had lesions in both hocks—what we would call bilateral lesions—did start fewer races than those that only had a lesion in one leg. We also found that horses specifically with lesions of the lateral trochlear ridge (LTR)—a particular area of the hock joint—started fewer races as 2-year-olds than horses with OC lesions in other locations in the hock.”

This latter observation lends support to a previous study that reported poorer outcomes for LTR lesions in surgically treated horses, noted McCoy.

She also noted that some of the study's unexpected findings related to differences between trotters and pacers. The researchers found that hock OC lesions were more common in trotters than pacers, while lesion location within the joint tended to vary between the two groups.

“It’s possible that the biomechanical differences between the gaits may influence which OC lesions heal and which go on to form permanent lesions,” said McCoy, adding that genetic risk factors could also be at play. “Pacers and trotters are bred very distinctly from each other in modern Standardbred racing, so it’s possible that the underlying genetic risk—which we know accounts for up to about 50% of the risk for getting OC—may account the difference between the two populations.”

Both are hypotheses the researchers hope to explore in future studies.

The study, “Short- and long-term racing performance of Standardbred pacers and trotters after early surgical intervention for tarsal osteochondrosis,” will appear in an upcoming issue of the Equine Veterinary Journal

About the Author

Lindsay Day, REMT

Lindsay Day is a registered equine massage therapist and freelance health and science writer. She and her horse, A.J., are based in Ontario, Canada, where Day is currently pursuing an master’s of science in population medicine at the University of Guelph.

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