It was another consecutive scorching July afternoon in North Texas when my trainer called after noticing my Thoroughbred gelding Memphis wasn’t sweating despite the intense heat. He was standing by himself under the shady umbrella of an oak tree, panting heavily. The other horses in his herd were streaked with sweat, but Memphis’ coat was bone dry. I rushed out to the barn after work, gave him a long, cool bath and let him dry under a fan until I could find longer-term solutions.
Salt. Electrolytes. Acupuncture. One AC. Beer. Cold baths. Fans. I tried everything and anything to help Memphis sweat during the brutally hot Texas summers after my vet suspected anhidrosis, and using a multi-pronged approach, I was able to successfully manage his condition for the next 17 years of his life.
It turns out that my concerns were well founded. To lower their core temperatures, horses shed 65 to 70 percent of their body heat through sweating. When a horse doesn’t sweat, it severely limits his ability to maintain a safe internal body temperature. This can be extremely dangerous and lead to heat stroke, heat exhaustion, and even death if the horse’s vital organs start to shut down.
The mechanism that triggers anhidrosis still isn’t well understood. “It’s thought that the response to the circulating ‘fight or flight’ hormone epinephrine is switched off in the sweat glands, although how that happens is a mystery,” explained Robert J. MacKay, BVSc, PhD, DACVIM, a professor at the University of Florida College of Veterinary Medicine.
While anecdotal evidence suggests that horses relocated from cooler, drier climates to hot, humid coastal areas tend to struggle more with anhidrosis, horses native to humid climates are also afflicted.
“A predisposed horse will rarely become anhidrotic in a temperate or cold climate. It takes exposure to heat and humidity for some period of time before the condition develops,” MacKay said. “The thought is that the sweat glands get overstimulated in those conditions and shut down after constant bombardment by epinephrine in the blood.”
The link to climate showed up clearly in a 2010 survey of 500 farms and nearly 5,000 horses in Florida, carried out by MacKay and his colleagues. Overall, more than 11 percent of the horses were anhidrotic, but farms in hotter southern Florida were five times more likely to have at least one anhidrotic horse than farms in the cooler north.
Some horses suffer acute but temporary anhidrosis that can be triggered by unusually hot and humid weather. Others have a chronic condition in which the sweat glands seem to be permanently affected. Horses with chronic anhidrosis tend to have trouble maintaining weight and often experience dry, flaky skin and hair loss. The good news, however, is that savvy managements strategies can help keep horses with any form of anhidrosis healthy, comfortable and performing their best.
Sweat: The Details
Sweating helps your horse regulate his body temperature, keeping it in a (resting) range of 98 to 101.5 F. He sweats to cool himself in hot weather, during exercise and in periods of stress such as a trailer ride. Here’s how the cooling system works:
- As the horse works, his muscles burn energy and generate heat. Circulating blood absorbs heat from the muscles and carries it to the lungs (where some dissipates when the horse exhales) and to the skin (where some radiates from the body).
- If the muscles generate more heat than the horse can unload through breathing and radiant cooling, the excess builds up. The horse’s core temperature begins to rise.
- The hypothalamus, a part of the brain that acts as the horse’s central thermostat, senses the increase and sends signals to the adrenal glands. The glands release the hormone epinephrine into the bloodstream, and it circulates to sweat glands located in the skin over most of the horse’s body.
- The sweat glands spring into action, pumping out sweat. It’s the evaporation of sweat from the skin, not the act of sweating, that cools the horse. The sweat carries heat from the skin surface as it evaporates into the air.
Spotting the Signs
Veterinarians can usually make a diagnosis based on a horse’s symptoms alone. The condition can also be confirmed through a specific test involving epinephrine injections to try and stimulate the sweat glands, MacKay said. But this is largely unnecessary because most horses present clear symptoms. Electrolyte analysis can also be helpful in management planning.
Initial symptoms of anhidrosis may include:
- Increased respiratory rate/panting (flaring of the nostrils)
- Decreased ability to cool down after exercise
- Little or no signs of sweating, when another horse would be drenched in sweat under the same conditions. (Some horses might not sweat at all; others might have minimal sweat under the saddle pad or bridle.)
- Lethargy
- High body temperature or fever
- Decreased water intake/dehydration
- Dull, lackluster coat
- Depressed appearance
- Poor performance
Recognizing What’s ‘Normal’
MacKay half-jokingly said that anhidrosis is easier to diagnose than to treat. While there is no one-size-fits-all treatment or cure for the condition, there are a number of remedies that can help manage it or reduce symptoms.
Top eventer and four-time Olympian Boyd Martin has owned several successful horses—including Remington XXV and Trading Aces (Oscar)—who developed the problem. When trying to interpret subtle signs of anhidrosis, Martin said it’s helpful to have a frame of reference for what’s normal and healthy—and what might be normal for your horse.
“Day to day, the horses with anhidrosis sweat less and pant more than others. It’s easy to make the comparison, because we have a lot of horses in training here,” he noted. “Oscar always sweated, but the other horses would be lathered in sweat, and he’d be only damp. He definitely wasn’t sweating enough for the amount of work he did.”
Martin credits daily beer, supplements and a new fitness program for helping get Oscar on track to win at the 2014 Red Hills International CIC*** and hit the optimum time at the Rolex Kentucky Three-Day Event the following spring.
Smart Management Strategies
Shady spaces: If your horse is turned out during the day, be sure he has access to plenty of shade. Whether there are enough trees in his pasture to provide cover or he has access to a run-in shed, shade is crucial to helping horses with anhidrosis stay cool.
Watering holes: Always provide access to clean, cool water to encourage your horse to drink as much as possible. Hydration is essential to prevent overheating. If feasible, provide access to a pond, additional water troughs, or even a children’s pool. Some horses will swim or splash themselves with water to stay cool. (Memphis was notorious for producing a mud pit in front of the water trough after using his muzzle to splash himself.)
Fans & misters: Keep the air moving as much as possible. When temps really soar and there is little to no access to breeze or shade outside, keep your horse stalled during the day with at least one fan for air circulation. Moving air carries heat away from your horse’s skin. If feasible, you might also consider installing misters or a misting fan for heat relief. Misters add water vapor to the air to lower its temperature.
Exercise wisely: Only work your horse during the coolest times of the day. Early mornings or evenings are usually best, but be cautious riding later in the day. (As hot as it was in my homebase of North Texas last summer, it often didn’t cool down enough to ride safely until well after dark—and sometimes not until after midnight.) If you typically ride outside in an area without shade, you might consider hauling to an indoor arena where the heat and humidity can often be better regulated.
You also will likely need to adjust your horse’s workload if he’s not sweating efficiently. Be sure to take plenty of walk breaks in between periods of harder work and offer him water regularly. Horses with anhidrosis also need considerably more time to cool off after exercise. I would typically walk Memphis out for about 20 minutes or until his breathing returned to normal.
When the heat was in full swing here, I took my jumping lessons and did more challenging rides early in the morning to ensure he was comfortable—and safe—while exercising. If I did ride in the evenings, we either did a light hack or wandered along the nearby shaded trails.
Cool baths: Whether exercised or not, horses with anhidrosis will always benefit from a cool bath. The water helps bring their core temperatures down to normal and provides overall relief from the heat. After bathing your horse, be sure to use a sweat scraper to thoroughly remove excess water and allow him to completely dry either under shade or in the barn with a fan before turning him back out in the sun. Otherwise, even a thin layer of water on his coat, especially in humid climates, can act as an insulator and trap body heat.
Watch his diet: “Although we don’t have proof, it’s widely held that high carbohydrate concentrates and hays are a risk factor, so grass hays and low carb/high fat concentrates are favored, especially as preventative,” MacKay said.
Know his normal vitals: Be aware of your horse’s normal vital signs and monitor them closely during his cool out. If his temperature, breathing and heart rates are falling and he’s alert and interested in grass and water, he’s recovering. If they’re still high half an hour after exercise or he seems dull or disoriented, he may be at risk for heat stroke. Call to your veterinarian right away to assess the situation.
Additional Support
While many popular remedies have been reported to help with the condition, MacKay said they’re scientifically hard to prove, especially since the cause of anhidrosis is still uncertain.
“Anhidrosis is a strange condition. It’s often as hard to understand why it disappears as it is to know why it develops. There is a tendency among affected horses for sudden spontaneous remissions, and therefore the remedies used during those remissions are usually touted as miracle cures. But the fact that those same cures don’t necessarily work on the next set of horses is often overlooked. As for beer? I generally recommend that people give the beer to me. It will work just as well,” MacKay laughed.
That being said, I’ve personally spoken with a lot anhidrosis horse owners over the course of my personal horse life and career in the industry—mostly just out of curiosity to see what worked for them—and many swear by different tactics. In addition to careful management, there are also supplements and other nutrition-based approaches, as well as alternative remedies, that can help control anhidrosis symptoms.
One AC: Formulated specifically for horses with anhidrosis and backed by testing at the University of Florida, One AC contains ascorbic acid, niacin and l-tyrosine. This combination of amino acids and antioxidants work together to help stimulate the sweat glands. I consistently found that One AC worked best by starting Memphis on it in the spring, well before the summer heat set in. Owners who live in stifling hot or humid climates year-round sometimes keep horses with anhidrosis on permanently it and simply lower the dosage in the cooler months.
Hygain Sweat-Up: This supplement contains electrolytes like chloride, sodium and phosphate to support normal cellular functioning in the sweat glands. It’s also formulated with zinc and vitamin D to aid in the proper absorption of vitamins and minerals, as well as omega-3 fatty acids that play a key role in helping to support a normal inflammatory response.
Life Data Sweat Formula: Containing a combination vitamins and minerals, this formula was designed to help support normal sweating and promote the growth of healthy skin cells, which can also ramp up sweat production.
Dark Beer: Stout beers like Guinness contain B vitamins including thiamin, riboflavin, niacin, pantothenic acid, biotin, folic acid, B6 and B12—all of which are crucial for proper functioning of metabolic pathways. Yeast and hops also found in dark beers can encourage sweating, as well as aid in a healthy hindgut bacterial environment. You can add beer to your horse’s grain or water. If you go with the water option, just be sure to also offer your horse fresh, plain water.
Memphis was not super keen on the taste of Guinness at first; he preferred his beer with grain, so I gradually introduced it until I could get him to down a pint. (And there’s no need to worry about your horse getting drunk or buzzed on a small amount of beer. With their enormous body size compared to ours, horses would have to consume a substantial amount of beer before any risk of intoxication.)
Electrolytes: Supplements such as Restore SR, SmartPak’s SmartLytes or Farnam’s Apple-a-Day can help replenish any vitamins or minerals lost through sweat, including sodium chloride, potassium, calcium and magnesium. Electrolyte supplementation can also encourage your horse to drink more water, which will help rebalance his fluids and ensure proper digestion.
Salt: Adult horses need at least one ounce of salt per day. Since hay, grass and grain provide very little salt, horses are often lacking in this key mineral. Salt is essential for healthy nerve and muscle function. It also helps keeps fluids balanced and encourages hydration, especially in hot climates. You can add table salt to your horse’s grain (although, some horses aren’t keen on the taste of plain salt) or at the very least provide a salt block. Most horses, however, do not get adequate amounts of salt from blocks or licks. If your horse isn’t keen on salt’s taste, SmartPak’s SmartSalt provides a palatable a salt source in an apple-banana flavored pellet that’s easy to add to your horse’s daily grain ration.
Acupuncture: This ancient Chinese remedy has been used to treat various medical conditions in both humans and animals for more than 3,000 years, and interestingly, horses were among the first animals to be treated with acupuncture due to their vital importance in farming and warfare. Today, equine acupuncture is used to ease many conditions, including anhidrosis, and works by stimulating the acupoints to release beta-endorphins, serotonin and other neurotransmitters for systemic effects.
Making It Work in a Hotter Climate
When Memphis was first diagnosed with anhidrosis at the age of 7, I’d barely owned him for a year. I was not only extremely worried about his health and wellbeing, but I was also disheartened because I assumed our riding career would be severely limited during the heat every summer.
Much to my surprise, by recognizing and diagnosing his condition early on and by implementing a comprehensive treatment plan, I was able to manage his anhidrosis and even show throughout the early parts of summer. After last and this summer’s record-breaking heat worldwide, I fear that significantly more horses will struggle with this condition as their systems try to adapt to warmer temperatures. Fortunately, we have the tools to get ahead of situation, as long as we always pay attention to what our equine partners are telling us!
