Anhidrosis is a condition in which horses are unable to sweat properly. Horses that are unable to sweat will overheat much faster than a normal horse, due to the inability of the body to cool itself through sweating the heat produced during muscular activity. It can have a big impact on the horse's performance, as without the ability to regulate their body temperature during exercise, they are prone to overheating which limits their performance. In addition, it can put affected horses at increased risk of developing hyperthermia or heat stroke.
The disease usually happens in horses living in very hot, humid climates. It is usually easy to spot because affected horses will maintain a dry coat even after strenuous exercise in the heat. It is a problem for horses that are transported from Northern states to Southern states in the United States for a portion of the year. Some horses with equine pituitary pars intermedia dysfunction (PPID)
that are living in tropical climates develop anhidrosis and heat stress with secondary exercise intolerance. Once treated for PPID the condition will generally resolve. Onset of anhidrosis might be abrupt or gradual. Horses most frequently develop incomplete or partial anhidrosis, however chronic cases also occur. The more a horse is worked until they develop signs of heat stress, the more likely they will eventually develop anhidrosis.
Latest research studies conducted in Florida found that horses that come from sires and dams with a history of anhidrosis are more likely to develop anhidrosis. It has also been shown that the earlier anhidrotic horses can be treated, there is less chance of permanent structural damage to the sweat glands.