Anhidrosis

Up to 25% of horses in hot, humid environments lose their ability to sweat and subsequently suffer from hyperthermia as a result of impairment of heat loss.²⁴ In a more recent study that included more than 4500 horses from 500 Florida farms, the prevalence of anhidrosis was 11% at the farm level and 2% at the animal level.²⁵ Horses in training have been reported to have a higher frequency of anhidrosis, as are horses shipped to hot environments from more temperate regions; however, horses indigenous to hot, humid areas that perform less rigor­ously or not at all may also develop anhidrosis.^26-27 In addition to hyperthermia, clinical signs are poor performance, total or partial loss of ability to sweat, increased respiratory rates (three to five times normal), and dry, thin hair coats with areas of alopecia (see also Anhidrosis, Chapter 41).