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Anhidrosis in Horses and Electrolyte TherapyBy Kentucky Equine Research Staff · June 26, 2017

The sweat glands of most horses toil glitch-free for a lifetime, working tirelessly to moderate body temperature, excrete waste products, and help maintain the ecosystem of the skin. Occasionally, and often inexplicably, a horse will lose its ability to sweat, a condition known as anhidrosis. As with humans, sweating among horses is key to thermoregulation, so anhidrotic horses, sometimes called “non-sweaters,” pose significant challenges for their owners.

“The disease seems to be especially prominent in hot, humid climates, which makes the necessity of sweating all that more important,” said Kathleen Crandell, Ph.D., a nutrition advisor with Kentucky Equine Research (KER), Versailles, Ky. “It can come on suddenly or develop slowly over time and is most often associated with times when the nighttime temperature does not go below 80o F (27o C).”

Researchers estimate that 2-6% of horses suffer from anhidrosis. In one study* of 834 Thoroughbreds on central Florida farms, 6% of horses were affected. Horses in training and nonpregnant broodmares were diagnosed most often in this study, while young horses were infrequently affected. In a more recent, larger study**, one featuring just over 4,600 horses in Florida, researchers found about 2% of horses were anhidrotic.

Not all horses are similarly affected; some anhidrotic horses have decreased sweat production, some have areas of the body that stop sweating, while others completely stop sweating. Anecdotal reports reveal that dark-colored horses are affected more frequently than light horses.

Aside from lack of sweating, an acute episode of anhidrosis is characterized by labored breathing, flared nostrils, increased heart rate, increased body temperature, fatigue and possibly collapse. The greatest risk with anhidrosis is from the onset of heat stroke, which can be fatal if not dealt with immediately. Chronic cases are marked by increased drinking and urination, as well as a poor appetite. Horses with chronic anhidrosis might also have changes to their skin and coat, including dryness, scaling, regional balding, and itching, which is where another term for anhidrosis, “dry coat syndrome,” originates. Impaired performance is a problem among those horses chronically affected. Those that do not sweat at all might be unable to work altogether because of their inability to cool themselves.

Anhidrosis can be diagnosed by a veterinarian. A series of injections of dilutions of terbutaline, designed to stimulate the sweat glands, will help pinpoint non-sweaters. Blood work that includes an electrolyte analysis could be useful in developing a treatment plan.

Some horses that begin electrolyte supplementation are jump-started out of an anhidrotic state. Choose an electrolyte wisely. Restore SR (available as Restore in Australia), developed by the nutrition specialists at Kentucky Equine Research, provides innovative electrolyte therapy. Not only does it contain all of the important electrolytes—sodium, chloride, potassium, and magnesium—but it provides sodium in such a way that releases it slowly into the gastrointestinal tract, and this allows for sustained absorption. Restore Paste is also available and provides both oral and gastrointestinal comfort to sensitive horses that become irritated by traditional electrolytes.

In Australia, horse owners can also look for Endura-Max, and Endura-Max Paste.

“While electrolyte and salt supplementation are an integral part of a treatment plan for anhidrosis, if the solution was as simple as just adding electrolytes to the diet, then we would not have a problem with anhidrosis. There may not be a cure for the disease, but there are other ways to address the problem that also help the horse deal with the issues caused by anhidrosis,” added Crandell.

Additional management strategies, aside from moving the horse to a cooler climate, include:

  • Provide access to a shady environment during the daylight hours, and use fans to keep air moving in stalls or run-in sheds. Air-conditioned stalls are helpful for maintaining a cooler body temperature. Water misters may also be used to keep horses cool in extreme heat.
  • Nighttime turnout is helpful because there is more air movement and temperatures can be cooler than in stalls.
  • Offer a source of cool, fresh water at all times.
  • Exercise horses when temperatures are lower, such as in the early morning or late evening. Dampen the coat with water before starting exercise. Allow for plenty of cooldown time after exercise and monitor respiration rate. Splashing water on the neck, legs, and body will help bring down the body temperature. Watch carefully for any sign of heat distress.
  • Aggressive, regular grooming stimulates blood flow to the skin. Keep the hair coat clipped regularly during the hot season.
  • Some researchers believe supplementation with vitamin E might help anhidrotic horses.**,*** Natural-source vitamin E is superior to synthetic sources. Nano⦁E, a natural-source product developed by Kentucky Equine Research (KER), features nanodispersion technology, which ensures rapid bioavailability.
  • Consult with a veterinarian to discuss an appropriate treatment plan. Different treatment options are available, many of which depend on severity.

As of today there is no known cure for the disease, so all of the management, supplement, and medications recommended are for treating the symptoms and making the horse more comfortable.

*Mayhew, I.G., and H.O. Ferguson. 1987. Clinical, clinicopathologic, and epidemiologic features of Anhidrosis in central Florida Thoroughbred horses. Journal of Veterinary Internal Medicine. 1(3):136-141.

**Johnson, E.B., R.J. Mackay, and J.A. Hernandez. 2010. An epidemiologic study of anhidrosis in Florida. Journal of the American Veterinary Medical Association. 15:236(10):1091-1097.

***Zahoor, A., M.N. Manzoor, A.R. Usama, A. Ahmad, S. ur Rehman, and R.U. Khan. 2011. Epidemiology, electrolytes balance and treatment strategy of equine anhidrosis. Research Opinions in Animal and Veterinary Sciences. 1(1):4-7.