When is it too hot to safely ride?

Knowing how your horse thermoregulates will help you better understand how to keep him cool. Horses’ bodies produce heat when they work. They have several mechanisms that get rid of this heat.

The most important mechanism is evaporation. Most heat is generated from a horse’s large muscle mass. The cardiovascular system (the heart and blood vessels) move the heat from the muscles and organs to the skin. As your horse works, he produces sweat in glands in his skin. This sweat is composed of water and electrolytes (sodium, chloride, potassium, and calcium). As the sweat evaporates, it dissipates large amounts of heat, thus cooling your horse. To give you an idea of how much a horse needs to sweat to keep cool, the amount of heat dissipated by one liter of sweat equals just one to two minutes of maximal exercise, or five to six minutes of sub maximal exercise!

Other mechanisms include breathing out some of the heat through respiration. As your horse exercises, his respiration increases, thus releasing heat. Additionally, some heat is lost through convection/radiation where heat is moved directly from the skin to the environment.

Keeping these mechanisms in mind, there are several things you can do to help your equine partner stay cool:

1. Provide plenty of clean water. Your horse needs to replace that sweat! Make sure the water is clean and not too warm. Some horses are particular about water temperature.
2. Get your horse fit. An overweight horse has a harder time moving the heat through all that fat.
3. Hose or sponge your horse with COLD water over the large vessels on the inside of the hind legs, belly, and neck. These vessels bring the heat to the surface, so you want to cool those areas. Be sure to scrape off the water as it will warm quickly. There are many Icing and Cooling products that can help.
4. Work in the morning or early evening when it is cooler
5. Provide shade. A run-in or trees are just fine!
6. Clip any horse with a heavy hair coat
7. Replace electrolytes lost in sweat. Summer Games Electrolytes, or Farnam Apple Dex, are good choices.
8. Keep your horse in a well ventilated stall with a fan. Remember that evaporative cooling? The fan will help! (Be sure cords are out of reach and plugged into a ground fault interrupter)
9. Put sunscreen or zinc oxide on any pink or white noses.
10. Provide a water misting system if possible (again … it helps with evaporative cooling!)

Sometimes we can’t avoid the heat. On those days, keep an eye on the Heat Stress Index. The Heat Stress Index is the sum of the temperature plus the humidity. For example: if the temperature is 80 degrees Fahrenheit and the humidity is 20%, then the Heat Stress Index is 100 (80+20=100). If the Heat Stress Index is less than 120, it is OK to ride. Start watching it if it rises above 120, at 150 your horse’s cooling system won’t work effectively. If it is greater than 180, your horse will be unable to thermoregulate.

Registered 2011 by Equestrian Collections
Author: Sallie S. Hyman, VMD, DACVIM, CVA

Information in this article is for educational purposes only and is not a substitute for evaluation by an equine professional. In particular, all horse owners should seek advice and treatment from a licensed veterinarian, such as TEVA, for their horses' medical care.

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