Equine Tracheal Mucus Associated with Airborne Particulates

According to recent study results, if an athletic horse is constantly exposed to microscopic airborne particles then he could experience enough inflammation and mucus to decrease his performance abilities, even if he doesn't exhibit any outward signs of respiratory distress.

"Poor air quality could contribute to the accumulation of tracheal mucus, which is known to be associated with poor performance in racehorses," explained Melissa Millerick-May, PhD, assistant professor of medicine at Michigan State University's College of Human Medicine.

In a previous study, Millerick-May and colleagues found that horses are often exposed to airborne particulates (i.e., from feed, bedding, and footing) when stabled and that these particles can reach the lower lung, potentially inducing lower airway inflammation.

"Although it seems implicit, there are a limited number of studies that have intimately looked at the relationship between the concentration and size distribution of small-diameter particulates and the presence of tracheal mucus and inflammatory cells in racehorses," said Millerick-May.

To better establish this relationship, Millerick-May and colleagues measured airborne particulate matter from three Thoroughbred racetrack stables in July, September, and November, at three different times each test day. They also examined 107 apparently healthy racehorses endoscopically to assign a "mucus score" and collected a tracheal lavage fluid sample from each animal.

Key findings were:

Sixty-seven percent of horses had tracheal mucus visible upon endoscopic examination;

  • Horses were more likely to have tracheal mucus if they were housed in enclosed stables or occupied certain stalls with higher particulate concentrations as compared to adjacent stalls, particularly when the concentration of large particles (greater than or equal to 10 microns in diameter) were elevated; and
  • Horses exposed to small particles (less than or equal to 2.5 microns in diameter) were more likely to have elevated neutrophil numbers in their tracheal wash samples--an indicator of inflammation.

"These results clearly support our hypothesis that there is an association between visible tracheal mucus, numbers of neutrophils in tracheal wash samples, and concentration of airborne particulates as measured in stalls," Millerick-May said.

The good news is that, according to Millerick-May, the solution to this problem is actually quite simple.

"Motivated stable owners/trainers can practice dust control such as dampening aisles before sweeping, removing horses from stalls during cleanout, opening doors and windows to improve ventilation, and to remember that just because you can't see dust doesn't mean that it's not there--it's what you don't see that can result in problems," she advised. "Stable air quality is of paramount importance for maintaining airway health and enhancing athletic performance."

The study, "Local airborne particulate concentration is associated with visible tracheal mucus in Thoroughbred racehorses," will appear in an upcoming edition of the Equine Veterinary Journal. The abstract is available on PubMed.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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