Objective—To determine the incidence of and compare the types of catastrophic musculoskeletal injuries (CMIs) sustained in Thoroughbreds and Quarter Horses during racing at 3 Midwestern racetracks from 2000 to 2006.

Design—Retrospective cohort study.

Animals—139 Thoroughbred and 50 Quarter Horse racehorses euthanized because of CMIs.

Procedures—Veterinary officials from 3 Midwestern racing jurisdictions provided injury reports for Thoroughbreds and Quarter Horses that sustained CMIs (which required euthanasia) and the total number of race starts for each year. The number of CMIs/1,000 starts was determined for each racetrack. Past performance reports for each horse with a CMI were evaluated.

Results—The total number of race starts (both breeds) at the 3 racetracks from 2000 through 2006 was 129,460, with an overall incidence of 1.46 CMIs/1,000 race starts. Incidences of CMIs among racetracks were similar. Of horses that sustained a CMI, the median age of Thoroughbreds at first race was 3 years, compared with a median age of 2 years for Quarter Horses. A larger proportion of Thoroughbreds sustained a CMI in a claiming race than did Quarter Horses, and a larger proportion of Quarter Horses sustained a CMI in a futurity trial than did Thoroughbreds. The most common site for CMIs in Thoroughbreds was the left forelimb (69/124 [55.6%]), whereas most CMIs in Quarter Horses involved the right forelimb (18/30 [60.0%]).

Conclusions and Clinical Relevance—Differences identified between CMIs in Thoroughbred and Quarter Horse racehorses should allow veterinarians to focus on horses and anatomic regions of greatest risk of CMI during racing.