Environmental Determinants of the Equine Athlete: Air Pollution Exposure, Performance Impacts, and Management Recommendations Across Equestrian Disciplines

Abstract

Ambient air pollution represents the single greatest environmental health threat worldwide and is a leading contributor to human morbidity and mortality. Although policy has significantly improved air quality in the United States (U.S.), climate change is reversing these trends. Warmer and drier conditions promote more frequent and intense wildfires throughout western U.S. and Canada, resulting in fine particulate matter (PM2.5) emissions that travel far from the source of smoke. Additionally, hotter climates promote ground-level ozone (O3) formation, a secondary pollutant that forms in the presence of heat and sunlight. O3 remains a persistent concern in many regions of the U.S., including the Colorado Front Range. While much is known about how air pollution impacts human health, little is known about its effects on domesticated animals. Athletes, especially those who exercise outdoors, have been identified as a particularly vulnerable group. Therefore, we identified equine athletes as a promising model, given decades of existing performance data and their primarily outdoor lifestyle. Our objective was to characterize the risk of air pollution exposure, explore the relationship between exposure and equine athletic performance, and develop evidence-informed management recommendations for horses during periods of poor air quality. Spatiotemporal analysis of air quality at U.S. Thoroughbred racetracks identified that all racetracks experienced levels of pollutants exceeding the National Ambient Air Quality Standards (NAAQS), and that PM2.5 and O3, remain key pollutants of concern with clear seasonal patterns and heterogenous spatial distribution. We then explored air quality exposure during pre-competition training, applying a distributed lag non linear model (DLNM) in a retrospective observational study to describe the relationship between training air quality and winning speed on race day, and how that relationship unfolds over time. Horses exposed to higher pollutant levels during training had slower winning speeds when compared to those exposed to lower levels, equating to approximately one horse-length slower. We then extended investigation into the sport of eventing to explore the relationship between event-level air quality and performance across the phases of dressage, cross-country, and show jumping. Our results suggested that worse air quality is associated with performance declines in dressage and show jumping. However, worsening air quality appears to benefit cross-country time penalties, with no discernible effect on cross-country jump penalties. These findings supported the development of expert-driven guidance on managing horses during periods of poor air quality. Through an iterative modified Delphi process engaging leading equine veterinarians around the world, we collated recommendations for the general management of all horses, including guidance for training and competition days. By using existing data, we established equine athletes as a promising sentinel model and filled a critical gap in the knowledge of how air pollution affects horses, emphasizing the need to incorporate air quality monitoring into equine sports. Future work must investigate mechanistic pathways underlying performance decline and equine-specific pollutant thresholds at which adverse health impacts are observed. Through the continued use of the equine athlete as a sentinel model or by applying this methodology to other animal species, this work can continue supporting efforts to best safeguard the health and welfare of all animals living under a rapidly changing climate.