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Anhidrosis in Horses

Anhidrosis - a look into the causes and some ways to control anhidrosis, or non-sweating, in horses. Written by Jayne Pedigo for Equisearch.
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Anhidrosis can affect all different types of horses and can be a debilitating condition. Anhidrosis can be caused by stress and can come on suddenly or develop over a period of time.

The Shock of Realization
I first noticed that Annapolis was having a non-sweating problem during the first summer that I owned him. I have mentioned this episode during an earlier feature article, but will tell the story again now. I was out riding Annapolis on the trails one weekend in early summer.

?Practical Horseman. All Rights Reserved.

?Practical Horseman. All Rights Reserved.

The day was hot, but as we trotted down the trail, the breeze generated as we moved along kept me relatively comfortable. It was when I stopped at one point to decide which route to take that I realized Annapolis was panting, hard. Panting so hard, in fact, that I was rocked in the saddle. I also noticed that his coat was completely dry, even under the saddle area. This inability to sweat had left him with no way to regulate his body temperature and he was dangerously overheated. He was exhibiting the signs of anhidrosis, or non-sweating.

Needless to say, I was extremely alarmed. I was close to the furthest point on my route from the barn, well away from any houses or roads. The first thing that occurred to me was to take Annapolis down into the creek that we were riding alongside. At one point the creek widened into what we called "the lake", which had easy access and a nice sandy beach. Once on the beach I removed Annapolis' saddle, led him into the water and began splashing the water onto his belly and thighs.

Almost immediately, he began pawing at the water and I jumped back in fright as he went down and rolled in about a foot of water. Trying to keep hold of the reins, I got pulled in up to my ankles. Annapolis got up as quickly as he went down and shook himself. I began to scrape the water off him with my hands and then resumed splashing his belly and thighs, while keeping an eye on his breathing, which began to seem less labored.

After his roll I took Annapolis back up to the path and into a shaded area among the trees and watched as his breathing very slowly returned to an acceptable level. I put his saddle back on and led him most of the way back to the barn, keeping to the shade as much as possible and only re-mounting when I got back to the road to ride the last mile home.

What is Known About Anhidrosis
After that incident, I consulted many books and spoke with my veterinarian to arm myself with information about the condition. I discovered the following:

  • In our area of the Gulf Coast, Anhidrosis affects approximately one in five horses.
  • It can affect horses of all breeds and all ages.
  • It is thought to be triggered by stress - exercise, heat etc.
  • It can come on suddenly, or develop over a period of time.
  • It can vary in severity - from a horse which sweats a little, especially under the saddle and between the hind legs, to one whose coat remains completely dry.
  • The horse's normal body temperature is between 99.5 to 101 degrees Farenheit and can reach as high as 104 after a strenuous workout.
  • In a normal horse, the temparature and respiration return to near normal fairly quickly after exercise.
  • In a horse with anhidrosis, the horse's body temperature and respiration will stay dangerously high, risking heat stroke unless steps are taken to help him cool down.

Helping the Horse Through Summer
My vet laughed as he told me that the best way to help a horse get over anhidrosis was to move to a cooler climate! Since that was not an option, we discussed ways in which I could keep Annapolis comfortable during the summer.

  • In severe cases, it is best to keep the horse stabled in a well ventilated barn, preferably with a fan to circulate the air and help the horse's system regulate itself. Night turn out is a good option for these horses.
  • One strange thing I did notice was that when Annapolis spent a week at Texas A & M, in their air-conditioned stalls during his bout with Equine Protozoal Myleoencephalitis, he sweated normally for the rest of that summer!
  • Less severe cases can be turned out during the day, provided there is plenty of shade. A pond in the pasture is a plus. Annapolis spent a lot of time wallowing in the pond in his pasture until the new owners of the barn I kept him at fenced it in as part of a flood control scheme.
  • Electrolytes, while very helpful to horses who sweat normally, won't be of much use to a horse with anhidrosis. However, they have been known to encourage sweating if the anhidrosis is accompanied by a potassium deficiency. They won't hurt the horse anyway, and may even help, so if you want to, go ahead and use electrolytes. (I found that using electrolytes before Annapolis stopped sweating made the condition less severe.)
  • Restrict exercise to the cooler hours in the morning or evening. Allow the horse plenty of cool-down periods at walk and monitor his respiration recovery during these periods.
  • I no longer go to shows in the summer. I prefer to avoid the stress of warming up and competing in the midday heat, for Annapolis' sake.
  • Cooling the horse by splashing water over the body, neck and legs, such as I did, help the horse's system cool down. As the heat from the horse's body is transferred to the water, scraping it off and splashing with more water will speed the cooling process.

Consult Your Veterinarian!
As always, the notes I have made here are not meant to replace veterinary care. If you suspect that your horse suffers from anhidrosis, consult your veterinarian. He will be able to make an detailed assessment of the severity of the case and will advise you accordingly. This related page: "Symptoms Giving Warning of Heat Stress in Horses" is full of good advice from Donald Stotts.

Anhidrosis Update
Check out my follow-up article, which details my experimentation and success with a new equine nutritional supplement, One AC.