Anhidrosis or "dry coat" is the decreased ability or complete loss of ability to sweat. Since horses are one of the species that rely on sweating to help keep their body cool, not being able to sweat can cause them to perform poorly or even collapse. Horses that live in hot, humid conditions no matter the age, gender and breed are most likely to gradually develop this condition.
The underlying cause of anhidrosis remains unclear. Experts believe either something is wrong on the stimulation end (such as with the neurotransmitter adrenaline) or something is wrong on the receptor end (such as decreased numbers of receptors or decreased sensitivity of these receptors). While no treatment exists, there are supplements that support healthy sweating by supplying electrolytes, neurotransmitter precursors and specific herbs.
Some horses with anhidrosis regain the ability to sweat when moved from the hot, humid climate to a cooler, drier one yet others don't. Additional tips to help keep horses cool include: