Radiographs of a yearling’s legs offer a unique glance into the horse’s athletic future, according to Albert Kane, DVM, MPVM, PhD, Post-Doctoral Fellow in Biomedical Sciences in the College of Veterinary Medicine at Colorado State University (CSU). At the American Association of Equine Practitioners’ recent convention, Kane presented findings of a landmark three-year study that was completed at CSU’s Equine Orthopaedic Research Laboratory with the support of the Keeneland Association, Fasig-Tipton Sales Company, the AAEP Foundation, Barretts Equine Limited, the Blood-Horse Charitable Foundation, and The Jockey Club.

With collaborators, Kane examined the X rays of 1,200 Thoroughbred yearlings from sales at Keeneland and Fasig-Tipton companies in Kentucky from 1993-1996. Kane and his colleagues reviewed and categorized changes in the horses’ joints, including fetlocks, knees, hocks, stifles, and feet. Next, they consulted racing records from The Jockey Club Information

Systems, and mailed questionnaires to buyers of the yearlings, after which they compiled and analyzed the results.

It was discovered that there were radiographic changes that buyers have avoided for years that do not pose a threat to a horse’s performance. However, there were some changes not previously recognized as harmful, that now are thought to compromise an athletic career.

Clearly not associated with lower racing performance in young Thoroughbreds were flattened areas on the sagittal ridge or condyles of the third metacarpus, circular lucencies (light areas) and vascular channels (linear lucencies) in sesamoids, and circular lucencies in the ulnar carpal bone (a bone of the knee). Buyers who once balked at these findings on sale films might want to reconsider yearlings which have these changes.

Clearly associated with lower performance in horses were palmar supracondylar lysis (bone resorption just above and behind the condyles of the cannon bone) of the third metacarpus (MC3), and enthesophyte formation on proximal sesamoids (mineralization where ligament attaches to bone). Horses with fragmentation at the top of the long pastern bone on the front of the hind limb were half as likely to start a race, and animals with changes at the dorsal medial intercarpal joint (front inside area of the knee) were one-third as likely to start as unaffected horses.

"There was no indication from this study that an association exists between radiographic changes of osteochondrosis (OCD) and improved racing performance in Thoroughbreds," he assured. While that statement might not seem surprising, some researchers have suggested that a genetic link exists between osteochondrosis and better performance in Standardbreds. "There was just no indication of that in these data," said Kane.

A study this detailed had never been reported in the Thoroughbred industry, but similar studies have been done with Standardbreds. Fragmentation of the long pastern ligament in the hind limb was much less common in the Thoroughbred yearlings, whereas fragmentation in the dorsal fetlocks of Thoroughbreds and Standardbreds was similar. According to Kane, surgical intervention could explain why no effects on racing performance were detected for many lesions like OCD or subchondral bone cysts.

Kane explained that the results suggest some new areas for concern (the palmar supracondylar lysis of MC3, for example), and confirm some problem areas.

"Veterinarians will still need to use their clinical judgement at the sales," says Kane. "But for several lesions, they now have some hard data to back up their recommendations."

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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