The effect of selected factors on length of racing career in Thoroughbred racehorses in Poland

The aim of the study was to develop a profile, and to examine factors affecting the length of the racing career of 1759 Thoroughbreds (872 males and 887 females) in Poland. Product-limit survival analysis and Cox proportional hazards model was used to determine whether sex, age at first race, month of birth, trainer and performance at first season (money earned and number of starts) were associated with racing career duration. Comparison of the survival curves for males and females revealed a difference in career length between the two sexes, with males having a significantly higher survival probability than females (hazard ratio = 0.66). Age at first start and performance during the first year of racing were significant predictors of length of racing life while those that first started at two years of age were less likely to cease racing than horses that first started at the age of three years (hazard ratio = 4.49). Females, which had a smaller number of starts during their first racing season had longer careers. Since overlapping age at first start, racing performance and effect of the trainer it is difficult to assess the latter effect. The effect of month of birth on subsequent length of racing life was not found significant.