The Norman Transcript

May 17, 2013

How to guard against heat stress in horses after weather shift

For The Transcript
The Norman Transcript

NORMAN — Oklahoma temperatures will be soaring upward soon, and that can be quite a shock for horses, especially given how Old Man Winter hung on until recent weeks.

“The sudden shift from cooler-than-normal temperatures to those associated with summer underscores the need for horse owners to monitor their animals closely,” said Heath Herje, ag educator for Oklahoma State University Extension in Norman.

During exercise, there is a significant increase in the amount of heat produced by working muscles. 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.

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 buildup of heat.

“Heat stress from exercise can result when the environmental temperature is high,” Herje said. “Commonly observed signs of heat stress are profuse sweating, rapid breathing rate and rapid heart rate.”

Some horses are anhidrotic, meaning they have little or no ability to produce sweat. Since heat loss is mainly dependent on convection (wind) and evaporation (sweating), anhidrotic horses are prime candidates for heat stress.

“Owners who suspect a horse to be anhidrotic should consult with their veterinarian, as diagnostic tests exist that can be conducted,” said Dave Freeman, Oklahoma State University Extension equine specialist.

Early stages of heat stress can advance into more critical symptoms associated with heat stroke. Symptoms include skin that is dry and hot, pulse and respiratory rates much higher than normal and unusually high rectal temperatures.

“Horses that exhibit these symptoms require immediate attention,” Freeman said.

Freeman advises that the horse be moved to a shady area with fans or wind to provide ventilation. Cool water should be sprayed on the horse’s body and legs to help the evaporation process.

“In critical situations, the attending veterinarian may advise that ice packs be placed on legs and other areas that exhibit large veins surfaced on the horse,” he said. “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.”

Normally, a horse’s temperature is around 101. The critical temperature is around 104.

Equine owners should know how to identify heat stress in a horse before it progresses. Relieving the horse from exercise and cooling the animal’s body by fans and shade will help lower the stress and aid in recovery.

“Also, care must be taken that the horse doesn’t become dehydrated during long bouts of exercise,” Freeman said. “Generally, horses should be allowed to drink as frequently as they desire, unless they are showing definite signs of heat stress.”

Some recommendations suggest limiting free access to water when horses are extremely hot because of the chance of digestive upset.

For these times, an attending veterinarian may recommend that riders offer small amounts of water to the horse in frequent intervals before, during and after exercise.

“Replacement of water loss is important, so monitoring the animal’s intake and level of dehydration is critical,” Freeman said.

One test that can 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. Finally, don’t 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,” Herje said. “This heat must be released from the horse’s body through respiration and sweat. The commonly used practice of walking a hot horse guards against placing it in an area void of air flow.”

The length of cool-down procedures will depend on the amount of work, the environmental conditions and the individual horse. Herje and Freeman said horse owners who use these procedures and who know the signs of heat stress in horses can help prevent heat stroke in their animals.