Beneath your helmet, your head feels hot and sweat drips off your face as you ride. Your horse’s neck is soaked, and your reins are slippery and lathered. The more you call for an effort from your horse, the more sluggish he seems. Despite moving across firm ground, it’s as if his legs suddenly are mired in deep footing, with the ground holding him down. Your horse has run out of steam–or more correctly speaking, his body is boiling over with too much heat. He has reached a dangerous state of exhaustion. You pull him up, yet his muscles remain quivering, he’s panting, and his nostrils are flared. Could you have foreseen this development? Could you have prevented your horse from pushing the red line into the danger zone? Let’s examine how heat stress develops, what signs you can monitor, and how you can prevent it.

The Buildup of Heat

A distinction can be made between heat stroke and heat stress. Heat stroke can occur over a relatively short period of time, as in the case of an unfit athlete worked strenuously in high ambient temperatures or horses confined in poorly ventilated, hot trailers. Heat stress, also known as heat exhaustion, usually results from protracted fluid and electrolyte loss during exhaustive exercise. The exercise might become exhaustive as a result of high ambient temperature, poor conditioning, lack of normal sweating, etc. A sunny day contributes to high ambient temperatures. Warm air temperature and high humidity prevent a horse from adequately dissipating internal heat from his body (i.e., the mechanisms of heat dissipation are overwhelmed and/or inadequate).

With each stride, the muscles of an ex