Anhidrosis is a common problem in sport horses training and competing in hot humid conditions. Horses reduce their body temperature during exercise mostly by sweating. As sweat evaporates from the body surface, the body heat is reduced. They can also dissipate heat by respiration. Cool air enters the lungs and cools the blood flowing to the muscles and hot air is exhaled. During hot and humid conditions, the rate of evaporation of sweat is reduced and breathing in hot, humid air does little to cool the blood. The horse's coat is also a great insulator and can act like a wet suit keeping a layer of heat next to the skin if the sweat is slow to evaporate or is not scraped off.
Sometimes it is difficult to know if your horse is sweating enough. Some early signs may be reluctance to work, panting, sweating only under tack or a sticky dry coat. Some horses sweat more than normal in the months before they stop sweating. Horses with concurrent lung disease like heaves are at a greater risk of heat stroke because they have limited ability to cool themselves by respiration.
The sweat glands are highly innervated and are stimulated by the sympathetic nervous system (fight or flight response). The mechanism of anhidrosis in horses has not been determined but In chronic cases, the sweat glands are atrophied, suggesting multiple bouts of heat stroke may lead to more severe symptoms over time.
In people, some causes have included congenital, metabolic and autoimmune diseases, skin damage and drug induced causes.
In TCVM, the Heart controls the sweat glands and the Lung controls the exterior of the body and the Wei Qi (immune system). The balance between Yin and Yang control the body temperature. The Yin is like the air conditioner while the Yang is like the furnace. Summer Heat is one of the 6 pathogens in TCVM and can damage the Heart and Lung Yin so we view anhidrosis as a Heart and Lung Yin deficiency.
Treatment principles in TCVM include acupuncture, herbal and food therapy in addition to environmental modification like monitoring body temperature during exercise, working in cooler weather, taking frequent breaks in the shade, and cooling with water and scraping to help speed evaporation. During pasture and stall time, horses should always have access to shade, fans, salt, electrolytes and cool fresh water.
The NOAA heat index chart can help you determine when it is unsafe to work your horse if he is prone to anhidrosis. In south Florida, we are in the extreme caution zone for most of the summer. Due to our high humidity, even in the early morning or late evening. You may have to be vigilant about cooling before, during and after your horse's work out or you may choose to give them some time off during the summer.
Herbal therapy in combination with acupuncture has shown great promise in helping non-sweaters. Our recommendation is to start treatment in the late spring and continue through the summer until the heat index consistently falls below 90. This could include acupuncture once per month plus herbal and food therapy daily.
New Xiang Ru San is Dr. Xie's Herbal Formula made specifically for horses with anhidrosis. It contains a blend of Bian Dou (hyacinth bean), Xiang Ru (mosla), Hou Po (magnolia bark), Lian Qiao (forsythia) and Jin Yin Hua (honeysuckle flower).
Food therapy includes cooling foods to tonify the Heart Yin and pungent foods that tonify the Lung and increase sweating. A variety of foods from this list can be added to the horse's diet as treats or mixed into the feed. You can also check out our recipe for "green tea" ice pops on the feeding seasonally blog post.
Dark Malt based beer (Guiness)
Listen in to the new Driving Radio Show on Horses in the Morning for more TCVM info ! This month our Tremont training tip from Keady Cadwell is how to teach your horse to drive safely in a group, Katie Whaley recaps the Lexington Carriage Classic at the Kentucky Horse Park and Abbie Trexler has some great news about the new ADS vest rule. Plus in the TCVM update, Dr. Wendy talks about non-sweating and managing your horse through the summer heat.