by Melissa Sykes

A horse comes in from a morning work wringing wet. The trainer feels he “got something” out of the work. Another horse is lathered going to the post – his conditioner groans that he’s “washed out.” Yet a third animal is as “dry as a cucumber,” and the jockey expects a huge effort.

What these horsemen are observing is sweat. It is nature’s way of regulating body temperature. Some horses sweat profusely, others very little. And some do not sweat enough to keep themselves cool.

Anhidrosis is defined as “the inability to sweat in response to an appropriate stimulus.” The horse has sweat glands over nearly its entire body. When an animal begins to become anhidrotic, the amount of sweat on the flanks, the barrel, and the chest will begin to diminish. The sweat glands between the rear legs, on the face, and under the mane are usually the last to quit working.

Commonly referred to as “drycoat” or non-sweaters, anhidrosis is a condition that possibly has more impact on the racing industry than previously thought.

Non-sweaters are commonly believed to be confined to the tropical climates of the Gulf Coast of the U.S. and of Hong Kong, Malaysia, and India. Horses shipping from a more temperate climate (i.e. New York or Great Britain) to a hot, humid environment often experience some form of anhidrosis.

“The first documented case of anhidrosis,” said Diane L. Kitchen, DVM, Ph.D., “was in the 1920s when the British took their Thoroughbreds to India to play polo.”

Kitchen, a practicing veterinarian in the Ocala, Florida area, has treated many anhidrotic horses both in Florida and during her residency at Texas A&M University.

“I wanted to do my doctorate on anhidrosis 15 years ago and couldn’t get the funding,” she said. “There’s limited research money to go around, and it goes to other diseases.”

Research dollars have historically been spent on “dramatic diseases” where the economic impact is obvious. Anhidrosis is not dramatic, according to Kitchen.

“It can be very subtle,” explained Kitchen. “Horses can go months — even years — with a decrease in the ability to sweat.”

It is the subtleties of partially anhidrotic animals that are causing the most damage according to Dr. Sandi Lieb, a nutritionist at the University of Florida’s Animal Sciences Department.

“Sure there are non-sweaters up North,” Lieb said. “They just aren’t challenged enough” to exhibit the clinical signs of anhidrosis. As a horse exercises, she explained, it will sweat, and the sweat will evaporate, thus cooling the body. If the animal’s temperature remains high, a signal will be sent to the legs to slow down.

“A horse stops running when the body temperature gets to a certain (high) point,” noted Lieb.

An animal that a trainer may feel is just a “poor performer” may, in fact, have a case of partial anhidrosis. Its body temperature is getting too high during performance, so the horse slows down.

“We use all sorts of different excuses,” Kitchen said. “The problem is the horse can’t cool himself.”

“A lot of horses have varying degrees of anhidrosis,” Kitchen continued. “Those that are partially anhidrotic take longer to start sweating and longer to cool down.” These animals’ systems have not totally shut down, but they are not sweating enough to cool them down.

“This makes it a very frustrating situation,” she said.

Signs that horses are having a problem cooling themselves down include exercise intolerance, panting, or even a clear nasal discharge.

“It will take an anhidrotic animal a long time to recover from exercise,” said Kitchen. “Their resting temperature will be higher than normal. You’ll also see an increased respiratory rate accompanied by nostril flaring.”

According to Kitchen, “The horse’s primary means of cooling is sweating.”

However, if the animal is not sweating enough to bring the body temperature down, the respiratory system will kick in.

“The body will begin pumping fluid into the lungs to get it to evaporate off the respiratory tract,” she said. “A clear nasal discharge will be secreted.”

Another symptom, dull hair coat, is seen in anhidrotic animals because the oils cannot get to the hair follicles.

“The glands that produce oil are next to the glands that produce sweat,” explained Kitchen. “The oils and proteins that distribute on the hairs are carried by the sweat. It’s a well designed system when it works because the oil (combined with the sweat) creates a better evaporative process” to dissipate the heat.

To help remedy the dry coat, Kitchen suggests replacing those body oils by topically applying a non-allergenic oil that does not clog the pores. A hair coat supplement will not help as the body is producing the oil – it just is not making it to the hair follicles.

Horses – especially those in race training – will begin to suffer weight loss because the body is working so hard at cooling. Loss of appetite is also evident when a high protein based feed is being fed.

“If you have to break down a large amount of protein, your body produces more heat,” Kitchen explained. “These horses will back off their feed.”

Management of these non-sweaters is possible if the conditioner is willing to go to the trouble.

Kitchen’s first choice would be to put the afflicted animal in an air-conditioned stall. This is how the problem is being dealt with in Hong Kong, where the heat and humidity can reach very high levels.

The scarcity of land available for housing racehorses in Hong Kong has led to the barns resembling condominiums. The animals ride from the ground to their stall via elevators. Since the entire building is enclosed, providing stalls with air conditioning is an easy task.

In the absence of air conditioning, Kitchen suggests using a fan that blows a water mist. “Water goes through the fan, creating a wind tunnel and shower at the same time.”

Kitchen believes that anhidrosis is not a curable disease but that it can be managed and that most horses born and raised in tropical environments such as Florida have the subtleties of anhidrosis.

“Sometimes moving that horse from here (Florida) to Georgia may start the sweating,” she said. “It doesn’t always take moving to New York to start them sweating.”

Both Kitchen and Lieb have seen anhidrotic animals begin to sweat once the hot Florida summer is over.

“It’s cyclical,” noted Lieb. “In July, the horses will go anhidrotic until about October or November, then they’ll begin to kick out of it.”

The cyclical nature of the disease, according to Lieb, lends credibility to the argument against year-round racing in the Southern states.

“I’m thoroughly convinced that Florida is not a place to keep horses in training during the summer months,” she said.

This past summer saw racing dates cancelled at Delaware Park, Prairie Meadows, and Monmouth Park because of the extreme heat experienced during July. Ironically, racing continued as normal in Florida during this time.

Another contributing factor being explored in ongoing studies at the University of Florida (UF) is a genetic predisposition for anhidrosis. During 2005, researchers at UF compiled the results of questionnaires completed by representatives of 500 farms that included information on 4,620 horses. The odds of anhidrosis were 6.87 times as high in horses with a family history of anhidrosis compared with the odds in horses without a history.

Lieb has always felt that there is a genetic predisposition with this condition. A broodmare she owns has become more severely anhidrotic with time. Lieb has documented foals from this mare exhibiting the same decrease in sweat pattern as that of their dam. Managing Anhidrosis

However, anhidrosis is not confined to the equine world.

During World War II roughly 30 percent of the U.S. military personnel experienced some form of anhidrosis. Research at the time yielded no cure except to remove the affected soldiers from the Pacific Theater to cooler, drier climates.

Removing an affected racehorse from the stable area of a southern track to one north of the Mason-Dixon Line continues to be the treatment of choice among trainers today.

“They (the horses) can be moved and become non-clinical,” said Kitchen.

However, “non-clinical” does not mean “non-anhidrotic.”

“Sending the animals north is not a cure,” explained Lieb. “You’re taking them to a place where they aren’t stressed as much” by the heat and humidity.

Many supplements and treatments have been tried on non-sweaters – everything from electrolytes to alcohol baths to a beer in the morning feed. Some of them work, but not in all cases. UF is currently studying the effect of acupuncture and the addition of certain Chinese herbs to the diet on the effects of anhidrosis, but the results of this research will not be available for some time.

Robert J. MacKay, BVSc, PhD, DAVCIM, Large Animal Sciences, University of Florida suggested the following when managing horses with anhidrosis: “Aim to keep cool and minimize stress. You want to reduce external and internal heat. To reduce external heating, keep horse in shade with a large box fan, preferably with an attached misting ring. Exercise only lightly and when the temperature is coolest, and then thoroughly cool out with hosing and evaporation. If a resting anhidrotic horse looks distressed or if its rectal temperature rises above 102 F, hose down the horse until temperature is about 100 F. If the horse’s haircoat is long, keep the horse clipped. To reduce internal sources of heat, eliminate all concentrate and feed grass hay only. If you must feed concentrate, try to substitute fat for carbs. Keep abundant cool fresh water available for drinking. It may be helpful to topdress hay or feed with one to three ounces of salt to encourage drinking. With weather like this, all horses should be managed as above - these conditions put all horses at risk to become anhidrotic.”

Hard to Diagnose

Kitchen feels that there are not more cases of non-sweaters, it is just that it is a condition that has become more recognized, at least in the tropical climates.

“There are a lot of horses with variable degrees of it that are never diagnosed,” asserted Kitchen. “No one knows what economic impact it has on the racing industry. The bottom line is we didn’t figure out that they don’t sweat enough.”

Symptoms of Anhidrosis

1. Exercise intolerance

2. Increased respiratory/flaring of nostrils

3. Resting body temperature higher than normal

4. Clear nasal discharge

5. Dull hair coat including thinning of hair on face, neck and chest

6. Weight loss

7. Loss of appetite

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