Objective: To identify risk factors associated with race-related sudden death in Thoroughbred racehorses in the US and Canada.
Animals: 4,198,073 race starts made by 284,387 Thoroughbred horses at 144 racetracks in the US and Canada between 2009 and 2021.
Procedures: Study data were extracted from the Equine Injury Database, which contains detailed records of 92.2% of all official race starts made in the US and Canada during the study period. Forty-nine potential risk factors were analyzed using univariable and multivariable logistic regression. Cases were defined as race starts that resulted in fatality within 3 days of racing, in which at least 1 of 5 codes relating to sudden death was recorded. Fatalities due to catastrophic musculoskeletal injury were omitted from the study cohort.
Results: 536 race starts resulted in sudden death, an incidence rate of 0.13/1,000 starts. Fifteen risk factors were significantly associated with sudden death, including horse age and sex, season and purse of race, race distance, and horses' recent history of injury and lay-up. Horses racing while on furosemide medication were at 62% increased odds of sudden death.
Clinical relevance: Associations found between previous injury and sudden death suggests preexisting pathology could contribute in some cases. The association between furosemide and sudden death prompts further study to understand which biological processes could contribute to this result.