Air pollution exposure during training impairs performance in Thoroughbred racehorses.

Abstract

BACKGROUND: Ambient air pollution contributes substantially to human morbidity and mortality, and athletes are recognised as a particularly vulnerable group. However, little is known about the impact of air pollution on equine athletes. OBJECTIVES: To explore the relationship between air pollution exposure during the pre-competition training period and race day performance among Thoroughbred racehorses that competed on California racetracks. STUDY DESIGN: A retrospective longitudinal study. METHODS: For each winning horse, pollutant exposure during the 21-day pre-competition training period was assigned using data from the nearest EPA air quality monitoring site to the racetrack where horses trained and competed. Exposure was characterised using the threshold Air Quality Index (AQI), with additional analyses evaluating fine particulate matter (PM) and ozone (O). A distributed lag non-linear model was applied to estimate associations between pollutant exposure during the training period and winning speed. RESULTS: Horses exposed to higher pollutant levels (80th percentile AQI = 58) during the pre-competition period had slower winning speeds when compared with those exposed to lower levels (20th percentile AQI = 32), with statistically significant decreases observed approximately 2-17 days before competition. Over the 21-day pre-competition exposure window, daily exposure to an AQI of 58, compared to an AQI of 32, was associated with a decrease in winning speed of 0.044 m/s (95% CI: -0.056, -0.032). MAIN LIMITATIONS: Limitations include the use of data from regional air quality monitors, which may not accurately reflect the quality of air horses are actually breathing, and the inclusion of only California racetracks, limiting generalisability. CONCLUSIONS: Pre-competition air pollution exposure was associated with slower winning speeds in Thoroughbred racehorses, highlighting the importance of systematic air quality measurement at equine racetracks.