With the arrival of summer and its soaring temperatures, it's time to pay extra attention to our equine companions. A prevalent and often overlooked issue during these hot, humid months is a condition known as anhidrosis - a condition characterized by a decreased ability to sweat in response to increased body temperature. This can be a significant concern, especially for performance horses, as thermoregulation in horses is mainly accomplished by sweating. To put it in perspective, between 65-70% of a horse's body heat is lost via the evaporation of sweat, and a humid environment can further decrease the efficiency of this cooling process.
Sweat glands in horses are densely packed in their skin, primarily exiting to the skin surface at a hair follicle. The sweat produced by these glands comprises proteins, electrolytes, and significant amounts of water. Electrolytes found in the sweat include sodium, potassium, and chloride, with these being found at a higher concentration than in the horse's blood, particularly potassium.
Anhidrosis is not exclusive to any particular age, sex, or color of horse. Both locally-bred and imported horses may be affected. Epidemiological studies have suggested a prevalence of between 2-6% of horses, though this may vary depending on the severity of the climate and the quality of the studies conducted.
In chronic anhidrosis cases, sweat glands ultimately atrophy. However, in acutely affected horses, these abnormalities are not yet present, suggesting a role for long-term downregulation of beta2 adrenergic receptors on sweat glands1.
Despite extensive research, there is no proven therapy for anhidrosis except moving the horse to a cooler climate. This not only helps manage the high body temperatures but also prompts horses to start sweating once in a cooler environment. Therefore, it is essential that horses living in hot climates are carefully managed to prevent high body temperatures from occurring1.
Here are some tips to help your horse through the summer heat:
Ride Early or Late: Schedule your riding sessions early in the morning or late at night. Temperatures and the heat index start climbing and are highest between 11 am and 3 pm.
Consider Acupuncture: A recent study performed at the University of Florida found that acupuncture and herbal medication might improve sweating in recently anhidrotic horses. Although the effect lasted less than four weeks after discontinuing treatment, it's a potential avenue to explore.
Cool Off Your Horse: Cold hosing and scraping water off as you’re rinsing is the fastest way to cool off your horse.
Provide Electrolytes and Minerals: Provide electrolytes or a salt/mineral block to help replenish lost minerals. This will help maintain appropriate total body electrolyte concentrations.
Ensure Access to Water: Make sure your horse always has access to water! A horse may drink a gallon or two within 15-30 minutes after a hard workout.
As the study and understanding of equine anhidrosis continue to evolve, it is important to remain vigilant in the care of our horses. Anhidrosis is a very serious syndrome affecting a substantial number of horses, but with the right care and attention, we can help manage this condition and keep our equine companions comfortable during the hot summer months. Current studies are also investigating the sweat genes of the horse and their genetic association to anhidrosis.