Musculoskeletal injury is the main cause of wastage in Thoroughbred racehorses worldwide, with nearly 30% of all fractures being pelvic and tibial stress fractures. Studies in California in the late 1990s suggested fast work increased the risk of injuries, while other studies in Kentucky implied high-speed exercise was protective. K.L.P. Verheyen, DVM, MSc, PhD, MRCVS, of the Royal Veterinary College (RVC) in London, examined risk factors for pelvic and tibial stress fractures during her PhD work for RVC that she completed at the Animal Health Trust in Newmarket, England.

Because both bones are situated in the hind legs, Verheyen grouped them for the study, which appeared in the February issue of Veterinary Preventive Medicine. “If we can identify modifiable risk factors for injury we might be able to change them and thus reduce the incidence of injury,” she says. “The USA studies looked back on the exercise history after the injury occurred, whereas we followed horses in training over a set period, so we were also able to look at records of slow speed exercise as well as fast.”

Thirteen Thoroughbred racehorse trainers in England participated in the study of nearly 1,200 horses who were in flat race training. They trained mostly 2- and 3-year-olds, but older horses were included in the study as well. From 1998 to 2000, trainers kept daily records on exercise distances, speed, and surface quality, and they noted any injuries. At the end of the study there were 148 total fractures, which included 41 pelvic and tibial stress fractures.

“The training methods were associated with the risk of injury,” says Verheyen. “The take-home message, as far as pelvic and tibial stress fractures are concerned, is that too much slow speed exercise is not good. This does make sense because we know that stress injuries are repetitive loading injuries. If you keep doing the same thing again and again, you risk injury