Kris Hiney, Oklahoma State University Cooperative Extension equine specialist, reminds equine owners that heat is produced as a normal by-product in the daily metabolic processes of horses.
“Heat production estimates can increase as much as 50 percent during periods of intense exercise as compared with heat production when the horse is at rest,” she said. “In response, a horse increases its sweating rate, moves more blood to the capillaries under the skin and increases its rate of breathing in an effort to release this build-up of heat. Heat stress from exercise can result when the environmental temperature is high.”
Commonly observed signs of heat stress are profuse sweating, rapid breathing rate and rapid heart rate.
Hiney said heat stroke can progress rapidly from heat stress if work intensity, environmental temperature or humidity overloads the horse’s ability to cool itself. Symptoms include skin that is dry and hot, pulse and respiratory rates much higher than normal at rest and following the cessation of exercise and unusually high rectal temperatures.
“Heat stroke is life threatening,” she said. “The owner should call an equine veterinarian immediately.”
The horse should be moved to a shady area with fans or wind to provide ventilation. Cool water should be sprayed on the animal’s body to help the evaporation process. If constant cool water cannot be applied, remove the excess water and spray again.
“Water that is not being evaporated traps heat, so it is important to monitor the situation closely,” Hiney said. “In critical situations, ice packs should be placed on legs and other areas that exhibit large veins surfaced on the horse.”
Veterinarians normally will give large amounts of fluid to the animal, and possibly give cold water enemas or drenches if the core temperature is extremely high.
The best recommendation is for equine owners to know how to identify heat stress in a horse before it progresses to heat stroke. Relieving the horse from exercise and cooling the animal’s body by fans and shade will help stop the onset of heat stroke.
“Normally, a horse’s rectal temperature is around 101 degrees Fahrenheit,” Hiney said. “The critical temperature, one that is characteristic of a life-threatening situation if maintained for any length of time, is 105 to 109 degrees Fahrenheit.”
Also, care must be taken that the horse doesn’t become dehydrated during long bouts of exercise. Large amounts of fluid can be lost through sweat. Be aware that the long-accepted practice of limiting drinking water to exercising horses has little scientific backing.
“Generally, horses should be allowed to drink as frequently as they desire, even during periods of exercise, unless they are showing definite signs of heat stress,” Hiney said. “Always have a source of clean, fresh water available, and make sure a horse has access to water after working or during prolonged bouts of exercise.”
A simple test that can be used to determine marginal water loss in a horse is the pinch test. When a section of skin on the neck or shoulder is pinched, the skin recoil will be immediate in normally hydrated horses. Dehydration will delay skin recoil.
Another practical test is the “effective temperature” test, used to help determine the environmental conditions most likely to result in heat-related illness in an exercising horse. This test combines ambient temperature with relative humidity.
“When the sum of the ambient temperature in degrees Fahrenheit and the relative humidity is around 150, the rider should use caution in exercising the horse so heat build-up doesn’t become critical,” Hiney said. “Most riding activities involving long or intense exercise should be postponed when figures approach 180.”
Finally, it is important not to overlook cool-down periods following exercise bouts, even when environmental temperatures are well within normal parameters.
“Large amounts of heat build up in a horse during work,” Hiney said. “This heat must be released from the horse’s body through respiration and sweat.”
Heat loss through sweat requires convection and evaporation. The commonly used practice of walking a hot horse guards against placing it in an area void of air flow. Some horse managers even use fans to promote adequate air flow.
“Air flow is vitally important for convection of heat off the horse’s body,” Hiney said. “The length of cool-down procedures will depend on the amount of work, the environmental conditions and the individual horse.”
Hiney added that horse owners who use these simple procedures and who know the signs of heat stress in horses can help prevent heat stroke in their animals.