Equine Anhidrosis: Researcher's 'Sweat Equity' Led to New Test

Florida researcher Robert MacKay, BVSc, PhD, Dipl. ACVIM, professor in the Department of Large Animal Clinical Sciences at the University of Florida, has developed a new means of assessing and quantifying quantifying clinical signs of horses that are incapable of sweating.

Anhidrosis--the inability to produce sweat--is problematic in athletic horses or horses residing in hot, humid conditions. It is currently estimated that approximately 6% of Florida horses are anhidrotic.

"Horses that can't sweat are incapable of dissipating body heat, particularly during intense exercise or when there are high ambient temperatures," explained MacKay. "Affected horses can develop high heart rates, hyperthermia, and exercise intolerance."

Based on an existing test that involves injecting small amounts of the drug terbutaline under the skin and visually determining whether sweat is produced or not, MacKay elected to inject increasing concentrations of terbutaline and measuring exactly how much sweat was produced.

Specifically, MacKay intradermally injected 10-fold serial dilutions of terbutaline sulfate ranging from 0 (control) to 1000 mg/l at 5 cm intervals on the necks of seven Thoroughbred horses. Absorbent pads were taped over each injection site immediately following the injection for 30 minutes. The mass of sweat produced at each concentration of terbutaline was then recorded.

According to MacKay, this modified sweat test will permit us to more accurately define horses with anhidrosis.

"Veterinarians will be able to state that a tested horse is anhidrotic because it has a sweat weight less than the 95% confidence limit at one or more concentrations of terbutaline," suggested MacKay.

Future research will include more horses of various breeds and both free-sweating and anhidrotic horses.

The study, "Quantitative intradermal terbutaline sweat test in horses," was published in volume 40 of the Equine Veterinary Journal.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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