Management of Horses with Anhidrosis

Management of Horses with Anhidrosis
5 July 2017 | Foran Equine


Anhidrosis is a serious condition of horses exercising in hot humid areas. In some horses the condition can be reversed, others require careful management of their condition to ensure continued athletic ability.

Anhidrosis, is a serious condition affecting horses, whereby, they cannot produce sweat. Horses with this condition are also known as “nonsweaters”, “dry coated” or “puffers”. “Shy sweaters” is another term for a similar condition, where the horses sweats lightly or in patches.

The first reports of anhidrosis were over 90 years ago, in horses transported from Australia to Malaysia. Nowadays, anhidrosis is typically seen in mature horses in hot, humid climate areas. It is particularly prevalent in the USA Gulf States, Malaysia, Singapore and Pakistan where, the incidence is up to 20% during the hottest times of year. The condition is often seen in heavily exercising thoroughbreds but, it can affect any breed of horse at any performance level. Historically, the condition was seen in horses transported from temperate to equatorial climate areas however, it can also be seen in horses native to hot, humid areas.

The diagnosis of anhidrosis is a relatively straightforward observation that the horse does not sweat after heavy exercise in a hot environment. The initial observation can be confirmed by injecting serial dilutions of adrenalin or clenbutarol into the skin under the crest of the neck. Both adrenalin and clenbutarol act directly on the sweat glands, stimulating sweating. In truly dry coated horses, these injections fail to stimulate sweating. In shy-sweaters, only high concentrations of either drug will stimulate sweating.

A horse’s principal means of cooling itself after exercise is via the evaporation of sweat. Approximately, 65% of body heat is dissipated in this way. The inability to sweat is a very serious condition, particularly in horses in heavy exercise or training. During exercise, the body temperature increases rapidly, at about 1oC per minute. Without sweating to reduce this, there can be a critical elevation in core body temperature. In extreme cases this can lead to seizures, collapse and death. Even in less extreme cases, horses affected with anhidrosis show signs of respiratory distress and prolonged heart rate and temperature elevation after exercise. These horses appear to pant after exercise, hence the alternative name for the condition of “puffers”. In conjunction they often exhibit, reduced exercise tolerance, poor performance, reduced appetite, dull coats and hair loss.

Anhidrosis seems to occur following continuous or prolonged stimulation of the sweat glands by adrenalin. This leads to desensitization to adrenalin or down regulation of adrenalin receptors, with the result that sweating is no longer stimulated by adrenalin release or injection. Affected horses have histological abnormalities of the sweat glands when skin samples are examined under a microscope.

While the condition and its risk factors are well recognised, advice on how to reverse the condition is varied and often based on local word of mouth. A summary of the main recommendations and the basis for implementing them in cases of anhidrosis follows below.

Interventions aimed at reversing anhidrosis:

    1. Remove the horse from hot, humid climate

Removing the horse from the hot, humid area is the only option known to completely reverse the condition. Re-acclimatisation takes some time, but when returned to a temperate climate, affected horses regain their ability to sweat.

    1. Electrolyte supplementation

A number of studies have shown that horses with dry coated condition, have reduced levels of electrolytes in their blood. As horses use and lose electrolytes in sweat, electrolyte supplementation in the diet is helpful in resolving the condition for some horses.

    1. Vitamin E supplementation

Vitamin E is an antioxidant vitamin and necessary for skin and overall health. Some studies have shown improvement in anhidrosis when horses are supplemented with Vitamin E or Vitamin E rich foods.

    1. Iodine supplementation

It has been suggested that anhidrosis is related to poor thyroid function. Although this link has not been proven, some success with iodine supplementation has been reported.

    1. Amino Acid supplementation

Supplementation with the specific amino acid, tyrosine has been reported to benefit some horses affected by anhidrosis.

Horses affected by anhidrosis that continue in exercise require supportive actions aimed at minimising temperature increases.

Interventions aimed to support anhidrosis horses:

    1. Reduce environmental temperature and humidity exposure

Where possible affected horses should be housed in cool, dry stables, with free access to cool water. Stable fans or air conditioning may benefit. Affected horses should only be exercised or turned out during the coolest times of the day. Pasture turn out for these horses should be shaded where possible. Changing to a high oil, low starch diet, as starches require metabolism by the body, which produces internal heat.

    1. Aid cooling after exercise

Cold hosing after exercise can help reduce body temperature quickly.

Anhidrosis is a serious condition of horses exercising in hot humid areas. In some horses the condition can be reversed, others require careful management of their condition to ensure continued athletic ability.