Factors associated with time until first race and career duration for Thoroughbred racehorses.

OBJECTIVE: To determine whether sex or foaling period were associated with time to first race start and whether sex, age at time of first race start, or inter-race period were associated with career duration for Thoroughbred racehorses in Australia. ANIMALS: 553 Thoroughbred racehorses. PROCEDURE: Race records through to the end of the 6-year-old racing season were obtained for each horse. Product-limit survival analysis was used to determine whether sex or foaling period was associated with time to first race start and whether sex or age at first race was associated with career duration. A Cox proportional hazards model was used to determine whether sex, age at first possible race, age at first race, or inter-race period was associated with time to first race start or career duration.
RESULTS: 472 horses (85.4%) raced. Time to first race start was not associated with sex or foaling period. However, males, who had their first race at a younger age and a greater mean number of rest days between races, had longer careers. The hazard ratio for career duration of males versus females, controlling for age at time of first race and inter-race period (0.27), confirmed that males had a higher probability of a long racing career. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that for Thoroughbred racehorses, sex and time of birth during the foaling season were not associated with time to first race. Male Thoroughbred racehorses that were raced less intensively or raced at a younger age were more likely to have long racing careers.