Glossary
Thermoregulation.
Direct answer
Thermoregulation is the control of body temperature through the balance between heat production and heat loss. Heat comes mainly from metabolism and working muscle; it leaves through the skin, expired air and the evaporation of sweat. Centres in the hypothalamus steer the whole process.
A common shortcut judges heat loss by air temperature alone. Humidity is decisive: evaporation is the main route, and sweat that does not evaporate does not cool. The ratio of body mass to surface area matters as well, since a large body generates a great deal of heat with relatively little surface to shed it.
Horses and humans share a marked capacity to sweat, which is unusual among mammals. Equine sweat, however, contains a surface active protein, latherin, that spreads fluid through a water repellent coat, and it carries more electrolytes than human sweat. With far greater body mass, heat loss becomes the limiting factor in the horse.
The evidence letter
Once a month: new syntheses, checked studies, and what has changed in the state of the evidence.