Horses are energy neutral, meaning they feel neither hot nor cold, when the ambient temperature is between 15 and 65 degrees Fahrenheit. Surprised? Summer heat can make horses far more uncomfortable than freezing winter temps. Fortunately, warm weather horsekeeping is pretty simple. Water, shade, air movement. Provide those three ingredients and most horses do just fine, especially if they have plenty of room to move around, a forage-based diet, and the company of other horses.
Some breeds are at a disadvantage in the heat, however. Our Icelandic mare, Fidla, can’t shed out her thick winter coat fast enough when Spring comes here in Phoenix, so Diana gives her a little help. This is a rare example of body clipping being in the horse’s best interest.
Traveling tip: To avoid dehydration of your finicky horse, start adding a little flavoring to the water at home. Add the same flavoring to the strange water and most likely your horse will drink it. Powdered lemonade, Jello, Kool Aid, even carbonated soft drinks are reported to work well for this.
Finally, here is a great article on how horses handle the cold.