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Also Known As

Dry coat syndrome, Puff disease, Sweating (lack of)


Losing the ability to sweat creates major problems for any horse, especially those living in hot, humid climates where night time temperatures remain in the 70's or higher. These high temperatures combined with high humidity do not allow the horse respite from high daytime temperatures, and anhidrosis may develop quickly or over a period of time.

It is thought that the continuous stimulation of the horse's sweat gland receptors causes them to quit responding resulting in the rapid breathing, noticeable flaring of nostrils, panting, and decreased energy that signal a case of anhidrosis.

The horse's temperature may rise to between 102 degrees to 103 degrees when inactive, and with exercise, the temperature may reach 105 to 108 degrees. Brain damage is possible once the horse's temperature exceeds 106 degrees.


  • Obvious lack of sweat during exercise
  • Panting
  • Rapid breathing with flaring of nostrils
  • Signs of dehydration as detected with the "pinch test"
  • Fatigue
  • Shortness of breath
  • Elevated heart rate
  • Rectal temperature over 103.5 degrees
  • Dry, flaky skin
  • Absence of sweating at times when other horses are sweating heavily
  • Respiratory distress


Typically, a horse sweats to move heat out of the body. When the sweat mechanism shuts down, the horse will begin to pant. The heart rate and respiratory rate will increase, and the horse's temperature will shoot up.

Blood flow diminishes to the outer layers of the skin, further limiting sweating action in an effort to conserve body water. As heat continues to build within the horse with no outlet, the horse becomes severely heat-stressed and may go into convulsions or a coma.

Horses often develop anhydrosis quickly and without obvious reasons other than heat and humidity. Usually, a combination of stressors cause a horse to stop sweating.

In a hot, humid climate where the temperature at night is over 70 degrees, up to 30 percent of horses show signs of anhydrosis. A combination of heat, humidity, stress, and pain from an injury are often seen with this condition. .

Higher temperatures cause the muscles and tissues of the horse to demand more oxygen. If increased metabolic needs are not met, the horse will suffer loss of muscular control and strength that may lead to accidents.


The best prevention is awareness of the horse's physical condition and the contributing components of anhidrosis. Recognizing when a horse is in danger of heat stroke and subsequently restraining the horse from further physical exertion may prevent the development of anhidosis.

Riding and exercising your horse during the coolest part of the day and keeping him out of the sun are simple, but effective, solutions. A readily available supply of cool drinking water is extremely important, and some horses like to stand in water for the cooling effect it has on their systems.

Keeping the horse in a shady environment with decent air circulation is important. In the stable, fans may be used to circulate and cool the air. Body clipping the horse, if practical, will allow more air close to the skin and help keep the horse's temperature down.

Taking the horse's rectal temperature and maintaining a temperature under 103.5 degrees is important. If the temperature goes higher, you should immediately take steps to cool the horse down by sponging or bathing his head, neck, and legs in cool water to return the horse's temperature to normal. As the horse cools down, his respiratory and heart rates will return to normal.


Once a horse develops anhidrosis, accommodations must be made to promote good health and vitality. Changes will need to be made in the environment, the amount and type of exercise, and the diet.

Anhidrotic horses will often attempt to find ways to cool off by seeking shady places, sources of water for standing or lying in, taking advantage of sprinkler systems, and finding places with good air circulation.

An owner can further help the horse by monitoring him carefully and providing fans, along with misting dispensers, or simply running cool water on the barn roof or in places accessible to the horse.

Riding and exercising the horse during the coolest part of the day is important and exercising during periods of high heat and humidity should not be routine.

Food supplements containing L-tyrosine and vitamin C have been shown to help horses maintain healthy sweating reactions.

Raymond LeRoy, a biochemist from Phoenix, theorizes that anhidrosis is caused by depletion of dopamine in the brain. If the horse is not producing enough dopamine to satisfy the needs of the brain, the cardiovascular system, and the sweat glands, sweating loses out to the needs of the brain and cardiovascular systems.

Research shows that One AC has been shown to provide the necessary raw materials to reverse anhidrosis when used properly with horses which have been taken out of training for about three weeks, to allow the system to respond to the supplement.

One AC is based on the theory of imbalance of dopamine to the nor-adrenaline/adrenaline complex with its ingredients: L-Tyrosine, Choline Bitartrate, Niacin, Pyrodoxine HCL and d-Calcium Pantothenate. Horses given this feed supplement begin sweating again within 10 to 14 days, according to LeRoy.

Of course, your veterinarian's guidance is important in determining what will work best for your particular horse.

Numerous anecdotal remedies have been employed to help horses with anhidrosis. "Lite" salt, a combination of regular salt and potassium chloride, has proven effective. Vitamin E supplements or thyroid supplementation have also been successful in treating anhydrosis. An old Cajun trick that some claim is effective is adding beer to the horse's feed.

Oral electrolytes may be added to the horse's water and making sure the horse has plenty of available drinking water is also helpful. Generally, being careful and aware of what is going on with your horse, especially under stressful conditions, will help either prevent anhidrosis or mitigate any damage caused by the condition.

Making sure that horses are healthy and up-to-date on worming and vaccinations going into the hot, humid season will help prevent development of anhydrosis. In some cases, horses may need to be moved to a cooler climate if at all possible.

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