Horses cool themselves by sweating and when they are unable to sweat, the condition is called anhidrosis. Onset of anhidrosis can occur suddenly after a horse has had a period of profuse sweating, or it can develop gradually over time. These horses can develop a complete or partial loss of sweating. In either case, these horses develop a high temperature and rapid breathing. Interestingly, the veterinarians at the University of Florida indicate many of the affected horses have loss of hair and a dull hair coat as well as depression, decreased appetite, and decreased water intake.
It is believed the condition develops due to overstimulation of the sweat glands that are stimulated by adrenalin in a hot and humid climate. The sweat glands are exposed to a high concentration of adrenalin and after a period of time become insensitive to it. Anhidrosis can usually be reversed by resting the horse in a cooler and less humid climate. Lots of horses with anhidrosis require medical treatment and certainly must be worked less because horses that do not sweat can become quite sick and can even die. A study has indicated that anhidrosis is most common in thoroughbreds and warmbloods and mostly occurred in horses in training. Also, it occurs more commonly in horses that are transported into hot and humid areas compared to horses native to these areas. High protein feeds, disease, and exercise tend to increase the chances of a horse becoming anhidrotic. So if your horse begins breathing hard even at rest and has a high temperature, infection is a possibility, but anhidrosis could be occurring.