Risk factors for interruptions to training occurring before the first trial start of 2-year-old Thoroughbred racehorses.

AIM: To quantify the time from the start of training to the first interruption and to identify horse and training risk factors for voluntary interruptions and interruptions due to musculoskeletal injury occurring before the first trial.
METHODS: A prospective cohort study was used to collect data on the training activity of 2-year-old racehorses, from 14 trainers in the Northern and Central Districts of New Zealand, over two racing seasons (2008/09 and 2009/10). Daily training data were recorded for each horse, including, distances worked at canter (>15 seconds/200 m), three measures of high-speed exercise (15, 13, and <12 seconds/200 m) and reasons why horses were not working. Competing risks survival analysis was used to investigate associations between risk factors and voluntary interruptions (no known condition or disease present), or interruptions due to musculoskeletal injury occurring before the first official trial.
RESULTS: A total of 205 horses spent 11,051 training days at risk of an interruption before the first trial. There were 134/205 (65.4%) cases of interruptions, of which 115/134 (85.8%) were voluntary interruptions and 19/134 (14.2%) were due to musculoskeletal injury. In the final multivariable models, the risk of voluntary interruptions decreased with increasing age at the start of training, and increased with the number of days off during training, but was not associated with gender. Females had a decreased risk of interruptions due to musculoskeletal injury compared with males. There was no association between the number of high-speed events and either voluntary interruptions or interruptions due to musculoskeletal injury. CONCLUSIONS AND CLINICAL RELEVANCE: The study highlighted horse and training risk factors associated with two types of interruptions occurring during training. Identification of modifiable risk factors may help to reduce the proportion of horses experiencing an interruption before the first trial start, reducing the number of lost training days and the associated cost.