Anhidrosis (non-sweating) in horses – symptoms
Extremely hot temperatures aren’t fun for anyone that works outside. Unfortunately, horses don’t get to escape to air conditioning; they have to live in the heat and are asked to perform in it as well. This becomes absolute misery for horses that stop sweating. They, like people, need to sweat for thermoregulation.
The inability to properly sweat is known as anhidrosis. The exact cause is unknown. Western medicine believes that this disease is triggered by one of the following: nerves not stimulating the sweat glands properly, the glands not responding to nerve stimulation, or clogged sweat glands.
There does not appear to be a predisposition for non-sweating based on age, gender, breed or coat color. It occurs most frequently in hot, humid climates, like the southeastern United States. While many think anhidrosis only affects new arrivals, a survey in Florida found more native horses suffered from non-sweating than the ones that were imported. The additional humidity in those areas decreases the efficiency of sweat evaporation which intensifies the problem.
This can become very serious for performance horses that are expected to continue with training. It’s no picnic for pasture horses that typically are under the sun all day either. When a horse’s core temperature rises, and sweat is not able to be produced to provide cooling, it can become very dangerous. At least 65% of heat is lost through the evaporation of sweat, so it is very important to notice anhidrosis early.
The horse’s brain is very sensitive to heat stress, and high body temperature can lead to incoordination, unwillingness to continue exercise, collapse, convulsion and even death. Performance horses must be monitored carefully to prevent overheating.
The absence of sweating is usually what owners or riders observe first. The area under the saddle is not wet or after a more demanding ride the horse will have minimal or no sweat at all. In many cases, the horse will sweat profusely for a short period of time, followed by patchy sweating and then reach the final phase of very minimal to no sweating.
Non-sweaters will have elevated respiration and heart rates as the body tries to get rid of the heat through the lungs, like a dog would. This can occur after exercise or even while at rest. Also watch for exercise intolerance, lethargy and lack of interest in drinking. Chronic cases will develop dry skin, loss of hair creating a ‘patchy’ appearance, lack of appetite, reduced water consumption, and poor body condition.
If you suspect your horse has anhidrosis, contact your veterinarian. Diagnosis can be made presumptively through clinical signs or definitively with testing using intradermal injections of epinephrine or terbutaline (QITST).