You could engage in the same amount of work more safely in the Fall or Winter, but put your mule at risk in the hot Summer months. The mule sweats more to dissipate the heat. The more he sweats, the more fluid he loses leading to dehydration. Long hair, blankets, coat sunburn and high humidity can impede sweat evaporation. If the heat cannot dissipate, the mule's temperature remains high.
Heat stroke occurs when the animal's body temperature remains high even after activity has ceased.
The mule's cooling mechanism has failed him. He is suffering heat stroke and this can be life threatening. F. However, as activity ceases the fit mule's temperature will rapidly return to normal as the mule cools down. If the mule is experiencing heat stroke, the temperature will remain elevated even after activity has ceased. Keep in mind, because of their higher tolerance, mules usually show clinical signs of pain and difficulty much later into the situation than horses would.