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
ANHIDROSIS OR PUFFER: the decreased ability to sweat in response to increased body temperature. thought that the sweat glands become habituated to the abnormal stimulus, stopping the standard sweat-producing response. Examination of the skin of some anhidrotic horses has found a high percentage of sweat glands that are abnormal, atrophied, or plugged. Some studies have tied anhidrosis to low thyroid function. Hypothyroid horses may resume sweating when they are treated for this condition, but indiscriminate thyroid supplementation to a horse with normal function can cause dangerous increases in heart and metabolic rates as well as weight loss and excitability. Thyroid supplementation should not be done without the guidance of a veterinarian.
Ideally, cool-region horses that will be asked to perform intense exercise in hot, humid conditions should be moved well in advance of the competition to allow them to adapt slowly to the climate. Up to three months of increasingly demanding exercise may be necessary before the horse gains maximum thermoregulation efficiency. Among the physiological changes are an expansion in plasma volume, increasingly stable cardiovascular function, and alterations in the sweating pattern. A horse that is asked for a high level of performance without a suitable conditioning period is at an increased risk for heat-related problems. Because fat metabolism releases less heat than starch metabolism, replacing part of the horse’s grain ration with a fat product may help anhidrotic horses stay more comfortable in hot weather. These animals should be given free access to fresh water, and electrolyte supplementation should be provided.
Management Strategies Additional management strategies, aside from moving the horse to a cooler climate, include:
Shade
• Provide access to a shady environment during the daylight hours, and use fans to keep air moving in stalls or run-in sheds. • Air-conditioned stalls are helpful for maintaining a cooler body temperature. • Water misters may also be used to keep horses cool in extreme heat. •Nighttime turnout is helpful because there is more air movement and temperatures can be cooler than in stalls. • Offer a source of cool, fresh water at all times.
Fan with misting nozzels on the Front
• Exercise horses when temperatures are lower, such as in the early morning or late evening. Dampen the coat with water before starting exercise. Allow for plenty of cooldown time after exercise and monitor respiration rate. Splashing water on the neck, legs, and body will help bring down the body temperature. Watch carefully for any sign of heat distress. • Aggressive, regular grooming stimulates blood flow to the skin. Keep the hair coat clipped regularly during the hot season.
Grooming
Some researchers believe supplementation with vitamin E might help anhidrotic horses. Natural-source vitamin E is superior to synthetic sources. Consult with a veterinarian to discuss an appropriate treatment plan. Different treatment options are available, many of which depend on severity. As of today there is no known cure for the disease, so all of the management, supplement, and medications recommended are for treating the symptoms and making the horse more comfortable. KENTUCKY EQUINE RESEARCH is an international equine nutrition, research and consultation company serving horse owners and the feed industry. The team at Kentucky Equine Research is there to help! If you have any queries about a suitable diet for your horse, or just want to check that they are getting everything they need, contact Kentucky Equine Research’s FREE Nutrition Consultation Service on 1800 772 198,
email advice@ker.com or visit www.ker.com October/November 2019 - Page 55
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