Anhydrosis: When Horses Don't Sweat It
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Pet Column for the week of July 20, 1998
Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Sarah Probst
Information Specialist
University of Illinois
College of Veterinary Medicine
Dr. R. Dean Scoggins, equine Extension veterinarian at the University of Illinois College of
Veterinary Medicine, knows what it is like to own a horse that doesn't sweat. "I brought a
stallion from Tucson, Arizona, that had never sweat in his life, to Illinois. We put him on a
feed additive specific for horses with anhydrosis. Later when we were working him, he
started sweating. He looked stressed and stopped moving because he was so scared by the
new sensation of sweating!"
Anhydrosis is the inability of a horse to produce normal amounts of sweat. "The extremes
range from a horse that has no functional sweat glands to a horse that produces sweat at a
rate lower than expected at certain degrees of exercise, temperature, and humidity,"
explains Dr. Scoggins. Some horses sweat normally in spring, but develop anhydrosis in the
summer as heat, humidity, and workload increase.
Horses depend heavily on sweating to regulate body temperature. Many horses raise their
body temperature to around 104 degrees during training. Exposure to a temperature of 106
degrees may cause brain damage. Sweat is critical so that evaporation cools the horse.
Sweat glands of horses with anhydrosis and of normal horses look the same under a
microscope. "Something is interfering with the physiological, chemical, or neural
transmission. We're not sure what, but there are a lot of theories," says Dr. Scoggins. "One
is that it is a metabolic failure and another is that the sweat glands become fatigued-perhaps
because the climate horses are worked in requires more sweating than the climate where
they were raised."
Besides a decreased amount of sweat or a lack of sweat, your horse may show intolerance
for exercise. They'll refuse to go forward or they'll pant. "It is physiologically impossible for
horses to breath through their mouths, but in distress, they'll try," says Dr. Scoggins. The
horse may play around more with the water pail, choose to stand in shade while other
horses are grazing, or roll in water and mud to cool down.
There is no specific treatment for horses with anhydrosis. The first step is management.
"Ride your horse in the coolest part of the day and keep him out of the sun. Fans may help,"
suggests Dr. Scoggins. "In extreme cases, horses may have to be stalled in air conditioning.
Some owners decide to relocate their horse to a part of the country with less heat and
humidity. Endurance horses and race horses might need to find a different job rather than
being highly competitive athletes."
Changes in diet can reduce heat production as well. Digestion of proteins and forages
generate a fair amount of heat. Go to a high-fat diet. From a caloric standpoint, it is more
easily assimilated with less heat generated by digestion.
Injections of epinephrine by a veterinarian help determine whether the dysfunctional sweat
glands have the capability to function. "If everything is working normally, the horse will start
sweating in a matter of minutes and drip continually until the dose is used up." Once it is
determined that sweat glands are functional, treatments may produce improvements.
As mentioned before, Dr. Scoggins has had success with feed additives-vitamin and mineral
supplements specific for anhydrosis. It takes one week to be effective. If treatment is
stopped, the horse stops sweating in approximately three days. Dr. Scoggins keeps his
stallion on the supplement throughout summer and at times in the winter when he knows the
horse will be working hard. Supplemented diets should be approved by your veterinarian.
Veterinary-recommended treatments for anhydrosis may include ONE-AC ﾮ,
Thyso-L ﾮ, vitamin E supplements, or thyroid supplementation. "Many horses may respond
to thyroid treatment but veterinarians must make sure the horse actually needs the
medication and prescribe the correct dosage for the horse's body weight. Excess thyroid
supplementation could cause hyperexcitability, loss of weight, increased heart rate, and
increased metabolic rate," warns Dr. Scoggins.
"Pay attention to whether your horse is showing distress during exercise and determine
why," encourages Dr. Scoggins. "Owners need to understand that not sweating is serious.
Once diagnosed, accommodations must be made for horses with anhydrosis." Be careful
and aware, but don't sweat it; most horses respond with treatment.
For further information on anhydrosis, contact your local equine veterinarian.