HEAT WAVES

Unlike dogs and most other animals, horses have sweat glands throughout their skin. Sweating creates “evaporative cooling”---as water changes from a liquid to a gas, it absorbs energy from its surroundings. In this case, that energy is in the form of heat from the skin and the air just above, leaving it cooler. But sweating is actually a horse’s secondary cooling mechanism. What is the first?

a. dilation of the capillaries in the skin b. heavy breathing c. flattening of the haircoat d. all of the above Answer: a. dilation of the capillaries in the skin. As blood flows through the body of a horse at rest, heat is absorbed from the muscles and organs. When the blood reaches vessels that lie just under the surface of the skin, the excess warmth dissipates into the cooler outside air. When a horse exercises, the amount of internal heat generated by his muscles increases. To maintain a constant internal body temperature, the excess heat must be dissipated faster. To accomplish that goal, the capillaries become dilated so more blood will be sent to the skin. If a horse continues working to the point that the capillaries cannot keep up with the heat he is generating, only then will he begin to sweat. Panting, like a dog, and flattening the hair to allow air to reach the skin more readily also have some cooling effect, but these are not the primary mechanisms horses rely on.