Mucus Accumulation and Effect on Performance

Susan Holmcombe, VMD, PhD, Dipl. ACVS, ACVECC, associate professor in the department of large animal clinical sciences at Michigan State University, told the group at the 50th annual American Association of Equine Practitioners (AAEP) Convention in Denver, Colo., Dec. 4-8, 2004, that mucus in the trachea of a racehorse can compromise his ability to perform. "The horse's ability to extract and use oxygen is vital to performance," she said, and added that mucus in the airways can prevent the horse from utilizing oxygen to the fullest.

Accumulation of airway mucus, she said, is common in young horses and often stems from inflammation. The number of racehorses affected approaches 33%.

However, she added that there were no definitive data on exactly what effect mucus had on racing performance, but there are indications that it might be associated with sub-par performance.

In an effort to find definitive answers, a study was conducted at Thistledown Racetrack in Warrensville, Ohio, during the race meet from April to December in 2002 and 2003. Each horse of the 527 horses in the study was checked via endoscopic examination of the nasopharynx, larynx, and trachea on a monthly basis. Here is Holmcombe's conclusion:

"The results of this study suggest that moderate to severe tracheal mucus accumulation is a risk factor for poor racing performance in Thoroughbred horses. Indeed, horses with little to no tracheal mucus placed nearly twice as well in a race compared with horses with moderate to large amounts of tracheal mucus.

"Infectious agents can cause airway inflammation and mucus accumulation. Tracheal mucus is also a symptom of inflammatory airway disease, hypothesized to be a response to the contaminants found in the air of stables. These contaminants include small particulates, antigens from molds and fungi, dust from hay and bedding, air pollutants, dust from the arena, and endotoxins.

"Therefore, recommendations to improve airway health and minimize tracheal mucus in horses may lead to improved racing performance. Emphasis should be placed on reducing environmental antigens by improving stable ventilation, decreasing dust in feed and bedding, and isolating horses with infectious disease."

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at or by calling 800/582-5604.

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