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  • Coastal Equine

Equine Anhidrosis

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Equine anhidrosis, also known as dry coat, is a disease in which a horse is unable to sweat in response to temperature extremes. The disease occurs in areas where hot and humid conditions predominate. In North America, the disease is most common in the Gulf Coast states. It has been estimated that 20 percent of horses in Miami, Florida are affected. Horses involved in training are more susceptible to the disease. There is no coat-color, age, gender, or breed predilection. The cause of anhidrosis is unknown. One theory suggests a malfunction in the horse’s sweat gland receptors. Low levels of chloride and other electrolytes may also play a role in anhidrosis. Anhidrosis has been associated with inefficient production of thyroid hormones (hypothyroidism). Abnormalities found in horses with anhidrosis include failure to sweat, increased respiratory rates at rest, exercise intolerance, elevated rectal temperature, and hair loss around the face, neck and shoulders. The skin may also be dry and flaky in these areas. Other signs may include lethargy, and decreased feed and water intake. Horses can suffer from different degrees of anhidrosis, ranging from partial sweating to complete absence of sweating. Some affected horses may continue to sweat under the mane, underneath the saddle, and on the abdomen. The diagnosis of anhidrosis is based primarily on recognition of the above abnormalities. Skin testing, using different concentrations of epinephrine injected directly into the skin (intradermal) can also be used. Normal horses will sweat at all epinephrine concentrations within 30 minutes of the injection. Horses with partial anhidrosis will sweat at only the highest epinephrine concentrations, while the completely anhidrotic horse will not sweat at any concentration. The most reliable treatment for horses with anhidrosis is environmental control. This may include providing a cooler environment for the horse or moving the horse to a cooler region of the country. Fans in the horse’s stall and misting the horse with water may aid in keeping the horse cool. Some suggest that adding electrolyte preparations containing sodium and potassium chloride to the water or feed may be beneficial in treating anhidrosis. Others suggest supplementation with vitamin E and selenium, iodinated casein, or thyroid hormone.

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