Anhidrosis: Something to Sweat About!

It's hotter than noon on the fourth of July! If you live south of the Mason Dixon, you're horses are feeling that heat too. They battle not only the heat, but also the humidity. Unfortunately, not every horse wins that battle. Anhidrosis is a condition in which horses have a decreased or complete inability to sweat. This condition develops in horses exposed to extreme heat/humidity and/or intense daily exercise. Without the ability to regulate their body temperature, they quickly overheat with body temperatures often rising higher than 103 degrees. The most widely recognized symptom is an increased respiratory rate. Overheated horses often stand with flared nostrils and appear to be in respiratory distress. If there is a water trough in their pasture, they will often splash themselves or stand in the trough. Heat distressed horses may become recombant and are at risk of heat stroke.

The underlying cause of anhidrosis is unknown although researchers suspect that excessive sweating and electrolyte depletion/imbalance may be a contributing factor. Studies have shown that there is no breed, age, or sex predilection. Furthermore, it can affect horses born in the South as well as those that are imported here. Since we do not know the underlying cause of this condition, there is no treatment that works in 100% of horses. Products such as One AC, electrolytes powders, herbal supplements, and dark beer have worked in some cases but not all. Acupuncture has also been successful in some cases.

Ultimately, the first line of treatment is to provide a cooler environment for the horse. For most owners, relocating an affected horse to a cooler climate during the summer is not an option. Therefore, owners should provide these horses with adequate shade (a shade shelter or barn) with large fans and misters. Providing access to a body of water or a sprinkler during turn out can help provide the horse with a means of evaporative cooling. Often these horses will regain their ability to sweat in the winter but will relapse again the next summer. Be proactive about providing a cool environment as the summer months approach. Adding electrolytes to feed as a preventive measure can help insure that depletion does not occur.

The take home message is that anhidrosis should never be ignored. It can rapidly become a medical emergency. If you notice that your horse appears overheated, check a rectal temperature (normal is less than 101.5 F) and quickly evaluate if they are sweating. If either are abnormal, start by cooling your horse with a water hose for 15-20 min. Remember to always use a sweat scraper to remove excess water when you are finished. With high humidity, excesss water can act as insulation on a horse that is not sweating and contribute to overheating.