Question: During one of my son’s riding lessons, the instructor pointed out that his pony was not sweating, despite the hot and humid weather. I had noticed on previous rides that he does a lot of “blowing” while being worked (like a dog panting except through his nostrils) but I had not noticed the non-sweating condition. Most of the other horses and ponies were wet with sweat, some even starting to foam. The instructor told him his pony had a disease … ? Any ideas as to what disease it may be? – Lynda

Response: The pony most likely has a case of anhidrosis, the inability to sweat to dissipate heat after exercise. This condition is often referred to as the “dry coat” or “non-sweating” disease. Horses that lose the ability to sweat efficiently are unable to maintain their body temperature within normal resting limits, so they pant to keep off heat – the “blowing” you spoke of. Anhidrosis is most common in the spring and summer, especially during unseasonable humidity when horses have less time to adapt to the changes.

While the exact cause of anhidrosis has yet to be determined, studies state that “anhidrosis syndrome is triggered in the hypothalamus gland by the stress of exercise and chronic dehydration under hot, humid conditions.” High humidity is the main trigger. Horses under hard training programs – particularly those on high grain diets, it seems – are more prone to developing the condition, although it has been known to affect all ages, breeds, and lifestyles.

The disease typically begins with extremely heavy sweating all over, followed by the development of patchy sweating under the mane and between the legs over a period of 1-3 months. As the ability to sweat is progressively lost, the horse will begin puffing and blowing forcibly after exercise in efforts to compensate heat loss. A dry coat, thinning hair on the head and upper neck, and poor stamina are also symptoms of the disease. In more severe cases, the horse may develop “heat overload” and collapse during strenuous exercise.

Since anhidrosis is nearly impossible to treat, especially if the horse must remain in a hot and humid climate, proper management of the disease is important.

1. Daily electrolyte supplements (like Humidix) were designed specifically for horses living in humid conditions. If the horse exhibits symptoms of anhidrosis during much of the summer but improves during the winter, it may be helpful to supplement feed with electrolytes before the start of summer. It is important to start the supplements just before the time when the horse normally develops the problem.

2. Many sources recommend supplementation with 1000 – 5000iu Vitamin E (like White E powder or liquid.)

3. A cool environment is essential. If the horse is stabled, air-conditioning or ceiling fans could be helpful. If the horse is kept at paddock, provide plenty of shade and water. Some anhidrotic horse owners find it works to keep the horse inside a cool stable during the day, then allow them to graze at night.

4. Avoid high protein diets in hot conditions. Oats can be replaced with lower heat-producing grains like rolled barley or corn. Half a liter of corn or 3/4 liter of rolled barley or 2/3 cup of vegetable oil will provide as much energy as 1 liter of oats.

5. Following exercise, hose off the horse with cool water (especially around the belly and flanks) and then immediately scrape him off. Repeat several times to reduce panting and blowing. Don’t allow the horse to drip dry; excess water in the coat retains heat and can interfere with body cooling.

— AE