Airborne particulates (PM10) and tracheal mucus: A case-control study at an American Thoroughbred racetrack.

This research study examines the link between the concentration of particulate matter in the breathing zones of horses and the buildup of mucus in their tracheas. It shows a strong correlation, suggesting that reducing particulate exposure can lessen the prevalence of tracheal mucus in thoroughbred racehorses.

Study Overview

• This case-control study involved endoscopic examinations of 649 Thoroughbred racehorses over a period of seven months.
• The selection of 113 cases and controls was based on the presence (Mucus scores or MS ≥ 2) or absence (MS = 0) of tracheal mucus. The horses were also age-matched to ensure parity in the comparison.
• The number of inflammatory cells in the horse’s tracheal lavage, a diagnostic test used to investigate respiratory diseases, was also counted.
• Using breathing zone monitors, the researchers measured particulate matter exposure during three distinct time periods: mid-day, evening, and overnight. The total average recording time was 17.5 hours per horse.

Findings

• The results showed that 23% of the horses in the observed stables had mucus scores of 2 or more, indicating a considerable presence of tracheal mucus.
• The recorded concentrations of particulate matter (PM10) in the horses’ breathing zones were similar to those previously reported in ambient conditions. This suggests that the horses’ breathing zone exposure was predominantly influenced by ambient PM concentrations.
• The study found that horses with visible tracheal mucus (cases) had significantly higher PM10 concentrations and counts of inflammatory neutrophils during the evening and overnight periods compared to horses without visible mucus (controls).
• A correlation was found between the numbers of inflammatory cells and the average concentrations of airborne particulates throughout the day.

Conclusions and Implications

• The study concludes that there is a significant connection between breathing zone particulate concentrations and both visible mucus buildup (MS ≥ 2) and counts of inflammatory cells.
• These findings imply that if the horses’ exposure to airborne particulates in their breathing zones is largely influenced by ambient PM concentrations, changes to racing stable management practices to reduce particulate exposure could significantly lower the prevalence of tracheal mucus.
• Reducing tracheal mucus is an important consideration as its presence can impact a horse’s performance.