Anhidrosis, or nonsweating, is a poorly understood condition affecting thousands of horses worldwide. Horses are most commonly affected in areas with hot, humid climates, such as in the southeastern United States. Let’s look at the causes of and treatments for this condition.

What Causes Anhidrosis?

Veterinarians and researchers are still trying to deduce the exact cause of this condition. Originally, it was thought that nonsweating was due to problems with acclimatization to hot weather; however, a survey of horses in Florida found that more native horses were affected than imported animals.

In normal horses sweating is initiated by stimulation of sweat glands, which are activated by nerve signals (neurotransmitters) called catecholamines. Recent studies have shown anhidrotic horses have higher levels of catecholamines than normal horses. It is possible that overstimulation of receptors by high catecholamine levels leads to desensitization. In addition, microscopic examinations of sweat glands in anhidrotic horses show abnormal changes in their cellular structure. This research suggests the condition is more likely a problem with the sweat glands and their response to nervous signals, rather than a lack of nervous signal production. Alternatively, many veterinarians suspect alterations in endocrine (hormone) stimulation of sweat glands