The danger of anhidrosis

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A horse dripping with sweat in the heat of the summer may be cause for concern, but it’s far more worrisome if he isn’t sweating at all.

Anhidrosis---the inability to sweat effectively or at all---is a poorly understood condition. The condition typically develops slowly, over the course of weeks, and is seen mostly in horses who live in hot, humid climates. And while it isn’t common—only an estimated 2 to 6 percent of horses develop it—the consequences can be significant and even dire.

Without adequate sweat to cool his body, and anhidrotic horse will quickly overheat, particularly if he is exercised in warm conditions. The horse may begin breathing very rapidly, even appearing to “pant” with an open mouth in an effort to dissipate body heat through the respiratory tract. Fatigue sets in quickly and the horse may even collapse with fatal heat stroke.

If you notice your horse is sweating less than you’d expect for the conditions, or even less than those horses around him, stop work and take immediate steps to cool him off by moving him to the shade and hosing or sponging him with cold water. (The risk of muscle cramping by putting cold water on a hot horse and a myth, so don’t worry about that.) Then call your veterinarian and mention your observation. There are tests that can be done to definitively diagnose anhidrosis.

Perhaps the best possible way to manage a horse with anhidrosis it to move him to a much cooler geographic location. Some horses even start sweating normally again when they are in a less stressful climate. But that’s not always possible. If you must keep an anhidrotic horse in a hot, humid area, there are steps you can take to keep him comfortable and safe:

• Keep him in a shaded, cool spot during the day. A stall or run-in shed with deep shade and very good ventilation may be sufficient, but fans may also be necessary to keep air moving. Some owners even arrange to keep anhidrotic horse into air-conditioned spaces, such as a garage, during the hottest times of day.

• Exercise the horse only in the coolest times of the day, such as the very early morning. You can also LIGHTLY dampen the horse’s coat before you begin work, allowing the water to serve the evaporative cooling function that sweat would have in a normal horse. Stop mid-ride to dampen the coat and continue riding. Be careful to avoid oversoaking your horse’s hair—a heavy layer of water will not cool as well as a light one.

• Experiment with supplements. There are number of different products reported by owners to have beneficial effects for anhidrotic horses. Many owners also swear Guinness stout beer helps keep anhidrotic horses regain some sweating ability.

• Keep close watch on your horse’s condition and check in with your veterinarian regularly. Research on this problem is ongoing and may yield better solutions.

This article first appeared in the August 2017 issue of EQUUS (Volume #379)