OH My how lucky are you, in the summer here it can get into the hundreds, I just turn on the barn fans, and they do just fine. The only time I had any problem was with a foal that was born when it was 105 and the heat index was also high, but his problems didn't last long. Horses have an inner cooling system as well, the blood vessels near the skin constrict, to help with cooling, they also dialate in the winter to help with heat. A really hot horse will show signs of respiratory distress, and be coated with sweat, then you hav e a problem. Otherwise, not to worry, horses are better able to handle the heat and cold then we are. It is usually only the new borns or the elderly that have any problems.