Anhidrosis in Horses

Anhidrosis can be a debilitating condition, especially for performance horses. During hot weather or hard exercise, horses with anhidrosis do not sweat. Since sweating is essential for cooling muscles and internal organs, a dry horse will quickly overheat and be in danger of heatstroke. Any horse may be affected, but this condition is much more common in humid southern climates.

What Is Anhidrosis?

Anhidrosis, also known as dry coat syndrome or non-sweating disease, is the inability to perspire. It occurs most commonly in the southeastern U.S., but horses throughout the country can be affected during particularly hot summer weather.

Symptoms of Anhidrosis in Horses

Anhidrosis may appear suddenly or gradually, with the first signs being exercise intolerance and slow recovery, particularly in hot weather. Other symptoms become evident as the problem progresses.

Horses with anhidrosis will sweat very little—or not at all—when other horses are wet with perspiration. Even during work, affected animals will not perspire, causing them to overheat quickly and breathe heavily in an attempt to cool down.

Eventually, a horse's skin and coat will suffer the effects of the condition, becoming dry and flaky with patches of hair loss.

Causes of Anhidrosis

The physiological cause of anhidrosis is not known, but the onset can be startlingly sudden.

• This condition appears most frequently in places temperatures and humidity stay high for long periods of time.

Approximately two percent of horses in Florida have been reported to be anhidrotic.

Diagnosing Anhidrosis in Horses

Veterinarians in the southeastern U.S. are familiar with anhidrosis and will likely diagnose the condition based on the owner's description and a physical examination of the horse.

Specific testing can be performed to confirm anhidrosis, although it is rarely necessary. This involves injecting terbutaline, a bronchodilator, into the skin to cause sweating around the injection site. Absorbent pads collect the horse's sweat for 30 minutes, then the weight of the pads is compared with the weight of normal horses' pads to show the degree of difference in perspiration volume.

Treatment

The treatment of anhidrosis involves symptomatic relief. Keep horses as cool as possible during hot, humid weather. Employ cool mist, fans, shade, or stall rest to lower the ambient temperature and maximize the horse's comfort.

If you must work your horse, restrict activity to cool mornings or evenings. Schedule shows and events for the times of the year when the weather is less likely to be hot.

Electrolytes, acupuncture, experimental medications, and dietary supplements have been used to improve anhidrosis, but there is little scientific research proving the efficacy of these treatments.

Prognosis for Horses with Anhidrosis

As long as a horse with anhidrosis is kept calm and cool during the hottest times of the year, it can live fairly comfortably. Overwork or extreme stress and heat can be dangerous, though, causing a horse to collapse, convulse, and even die.

How to Prevent Anhidrosis

There is no known protection against developing anhidrosis; even horses that are born and raised in hot environments can develop the condition.

Horses that already have anhidrosis will be more comfortable if they are moved north where long bouts of hot, humid weather are less common.