Air pollution is well-established as detrimental to human respiratory and cardiovascular health, yet its effects on animals, particularly equine athletes, remain underexplored. In a recent study, Kim et al. aimed to assess the impact of short-term exposure to ambient air pollutants—particularly fine particulate matter—on the performance of Thoroughbred racehorses.
Using data from 31,407 races across 12 California racetracks from 2011 to 2020, the researchers examined the association between air pollution and racehorse performance, measured by the winning horse’s speed. They gathered daily concentrations of PM2.5 (fine particulate matter), PM10 (coarse particulate matter), O3 (ozone), and NO2 (nitrogen dioxide) from the EPA for each race day. These were retrieved from air pollution monitors near each track.
Key Findings
Cutpoint analysis showed that racehorse performance declined with increasing PM2.5 concentrations between 4 and 23.6 μg/m³. At these levels, each 1 μg/m³ increase in PM2.5 was associated with a measurable decrease in speed (0.0008 m/s).
Analysis by racetrack revealed that the impact of PM2.5 varied geographically. Four racetracks (Del Mar, Ferndale, Fairplex, Golden Gate Fields) showed statistically significant reductions in speed associated with rising PM2.5 levels. These differences might reflect regional variations in pollutants, PM2.5 source (e.g., fossil fuels vs. wildfire smoke), or local horse management practices.
Other pollutants had inconsistent effects—while PM10 and NO2 showed positive associations with speed, these findings were not consistently significant. Ozone did not show a statistically significant impact on performance in this dataset, despite other studies linking it to respiratory distress.
Implications for Equine Athletes
These study results demonstrate that even low levels of PM2.5, well below the current U.S. National Ambient Air Quality Standards (35 μg/m³ daily average), can negatively impact equine athletic performance. The United States Equestrian Federation guideline to avoid outdoor activity above an AQI of 150 (~55.4 μg/m³ PM2.5) might not adequately protect equine athletes.
Given that horses have significantly greater lung capacity and ventilation rates during exercise compared to humans, even moderate levels of air pollution might impair respiratory efficiency, contribute to airway inflammation, or reduce oxygen delivery.
Recommendations
The study authors advised trainers and caretakers to monitor AQI daily and consider adjusting training and racing schedules during periods of elevated air pollution, especially wildfire season. Other barn air quality controls include using dust-free bedding, soaking/steaming hay, and limiting the use of blowers.
This research highlights an underrecognized environmental factor affecting equine health and performance. With rising air pollution from wildfires and urbanization, veterinarians can play a key role in advising evidence-based management strategies to safeguard equine welfare and performance.
Reference
Kim LD, Kreitner K, Scott DM, Seabaugh K, Duncan CG, Magzamen S. The effects of ambient air pollution exposure on Thoroughbred racehorse performance. Equine Vet J. 2025; 57(3): 712–722. https://doi.org/10.1111/evj.14415
Related Reading
- Impacts of Wildfire Smoke Exposure on Horses’ Lower Airways
- Diagnosing Respiratory Ailments in Horses: Wash or Lavage?
- Endotoxin Levels High in Indoor Equine Environments
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