Anhydrosis is the condition you mention—the absence of the ability to sweat—and is a big problem in all disciplines. However, it is more prevalent with endurance-type horses. Supplementation with an electrolyte replacement after the horse has worked hard will help. If the horse is regularly in hard work, it would also be a good idea to include electrolyte supplements in the horse's daily ration. Unfortunately, not much is known about how to prevent the condition. There is only one other supplement that is proven to help decrease the severity and incidence of anhydrosis, and that is the One AC you mention. These horses can still be ridden; just be careful not to overdo it. If you are too hot and miserable to enjoy the ride, he will probably be as well. It is extremely critical that you take care in the cooling out process and monitor your horse’s vital signs. Lots of shade and ventilation are necessary when cooling anhydrotic horses out. Hosing under the belly, chest, and between the legs is also crucial. Sometimes this condition will get better, but it might never get back to normal. There is evidence that horses moved to a cooler, drier climate after becoming anhydrotic may regain the ability to sweat more than those that remain in the hotter environment. This is the common fix for race horses that develop anhydrosis.

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