High-speed exercise history and catastrophic racing fracture in Thoroughbreds

Racing and officially timed workout histories were obtained for each of 64 Thoroughbreds euthanized during a 9-month period in 1991 at a California racetrack because of a catastrophic fracture incurred while racing. For each race in which a fatal skeletal injury (FSI) occurred, 1 control horse was randomly selected from the non-catastrophically injured participants. High total and high average daily rates of exercise distance accumulation within a 2-month period were associated with higher risks for FSI during racing, yet career patterns, such as age at first race or total proportion of career spent laid up, were not found to be associated with risk for FSI. A horse that had accumulated a total of 35 furlongs of race and timed-work distance in 2 months, compared with a horse with 25 furlongs accumulated, had an estimated 3.9-fold increase in risk for racing-related FSI. A horse that had accumulated race and timed-work furlongs at an average rate of 0.6 furlongs/day within a 2-month period, compared with a horse with an average of 0.5 furlongs/day, had an estimated 1.8-fold increase in risk for racing-related FSI. It is concluded that Thoroughbred racehorses that either accumulate large total high-speed distances or rapidly accumulate high-speed distances within a 2-month period may be at increased risk for FSI during racing.