No Sweat When your horse is unable to sweat it can rapidly accumulate more heat than it can easily eliminate, resulting in high body temperatures that can lead to incoordination, unwillingness to continue exercise, collapse, convulsions, and even death. A horse that lacks the ability to produce sweat in normal quantities has a condition known as anhidrosis. Such an animal is sometimes called a nonsweater or a drycoated horse. Horses that sweat lightly or only in patches such as under the mane, in the saddle area, and on the chest are known as shy sweaters. The condition seems to show up most often in Thoroughbreds, but Quarter Horses and horses of other breeds may also be affected. A veterinarian can make a definite diagnosis by injecting epinephrine under the skin. In normal horses, the area around the injection site will rapidly produce sweat. Anhidrotic horses exhibit a slow, weak, or nonexistent sweating response. Some degree of anhidrosis may affect up to about 25% of horses in hot climates. Among mature horses, there seems to be no correlation with sex or coat color. Often the problem is not noticed until a horse that has been conditioned in a cool climate is moved to a region with hot, humid weather. However, anhidrosis can also develop suddenly in horses that have been trained and shown exclusively in warm climates.
Typically, a horse might perform on an extremely hot day where it sweats excessively. Several days later, its sweat production is greatly reduced or absent. This sign is followed by other characteristics of the syndrome: reduced appetite, sluggish performance, dull coat, and hair loss on the face and croup. Core temperature rises quickly with exercise, and pulse and respiration stay greatly elevated after work as the body attempts to lose heat from the lungs. Anhidrotic horses are October/November 2019 - Page 54
BY KENTUCKY EQUINE RESEARCH
sometimes referred to as puffers because of this prolonged period of rapid breathing after exercise.
SENSITIVE TO HEAT
An inactive horse in a cool climate might not be bothered by diminished sweating. A more serious situation is encountered when a nonsweating horse is asked to perform hard work in a hot, humid climate. The conversion of stored energy to fuel for exercising muscles is not an efficient process, with more than three-quarters of the energy being given off as heat. It has been shown, in a horse performing treadmill exercise under hot, humid conditions that a rise in body temperature as rapid as 0.2° C every 10 seconds can occur. It is estimated that a horse on the crosscountry phase of a three-day event can produce enough heat to raise its body temperature more than 15° C. In a normal horse, about 65% of body cooling comes from evaporation of sweat, with another 25% attributed to respiration. A horse that is unable to sweat can rapidly accumulate more heat than it can easily eliminate. The horse’s brain is very sensitive to heat stress, and high body temperature can lead to incoordination, unwillingness to continue exercise, collapse, convulsions, and death. Horses that survive may have permanent brain damage.
CAUSE
The cause of anhidrosis is not known. Electrolyte supplementation seems to trigger a return to normal sweat patterns in a number of cases, and nonsweaters often resume sweating when they are moved to a cooler climate or when temperatures moderate in the fall. Acupuncture has been effective for some horses. One study has found evidence that a hormonal or metabolic imbalance may cause the horse to produce high levels of epinephrine. It is