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Equine veterinary journal2026; doi: 10.1002/evj.70186

Air pollution exposure during training impairs performance in Thoroughbred racehorses.

Abstract: 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. Objective: 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. Methods: 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). Conclusions: 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.
© 2026 The Author(s). Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2026-05-10 PubMed ID: 42108685DOI: 10.1002/evj.70186Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Objective Overview

  • This study investigated how exposure to air pollution during training affects the race performance of Thoroughbred racehorses in California.
  • The research found that higher pollution levels during training are linked to slower race speeds on competition day.

Background and Rationale

  • Ambient air pollution is known to negatively impact human health and athletic performance.
  • Equine athletes, such as Thoroughbred racehorses, may also be vulnerable to pollution’s effects, but this area has been understudied.
  • The study aimed to fill this knowledge gap by assessing the relationship between air pollution exposure during pre-competition training and race outcomes.

Study Design and Methods

  • The study was a retrospective longitudinal analysis focusing on winning Thoroughbred racehorses competing in California racetracks.
  • For each winning horse, air pollution exposure was assigned based on the nearest Environmental Protection Agency (EPA) monitoring site relative to the racetracks where the horse trained and competed.
  • Exposure was measured during the 21 days before competition, which corresponds to the critical pre-competition training period.
  • Air pollution metrics included the Air Quality Index (AQI), fine particulate matter (PM), and ozone (O3).
  • A distributed lag non-linear model was used to analyze the association between pollutant exposure during the training period and winning speed on race day.

Key Findings

  • Horses exposed to higher pollution levels (80th percentile AQI = 58) during the 21-day training period ran slower on race day compared to those exposed to lower pollution levels (20th percentile AQI = 32).
  • The slowing effect on winning speed was most pronounced approximately 2 to 17 days before competition.
  • Quantitatively, the difference in winning speed between exposures at an AQI of 58 versus 32 corresponded to a decrease of approximately 0.044 meters per second (m/s), with a 95% confidence interval between -0.056 and -0.032 m/s.

Limitations

  • Use of regional air quality monitor data may not perfectly represent the actual air breathed by individual horses during training.
  • The study was limited to California racetracks, which may affect the generalizability of findings to other geographical regions or racetrack environments.

Conclusions and Implications

  • This research provides evidence that exposure to air pollution during training can impair Thoroughbred racehorses’ subsequent race performance.
  • The findings underscore the potential value of systematic air quality monitoring at racetracks to mitigate negative impacts on equine athletes.
  • Improved air quality management could help protect the health and performance of racehorses, paralleling concerns already documented in human athletes.

Cite This Article

APA
Scott D, Seabaugh K, Kim L, Magzamen S, Duncan C. (2026). Air pollution exposure during training impairs performance in Thoroughbred racehorses. Equine Vet J. https://doi.org/10.1002/evj.70186

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English

Researcher Affiliations

Scott, Danielle
  • Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA.
Seabaugh, Kathryn
  • Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA.
Kim, Linda
  • Department of Environmental and Radiological Health Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA.
Magzamen, Sheryl
  • Department of Environmental and Radiological Health Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA.
Duncan, Colleen
  • Department of Microbiology, Immunology and Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA.

Grant Funding

  • D23EQ-454 / Morris Animal Foundation

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