Did you know that in a 99 mile endurance race a horse may produce enough heat to boil about 53 gallons of water? So how do you know if your horse is suffering from heat stress? There are a few simple measures of heat stress, and some easy fixes that can become part of your summer equine care regime.

Extremes in temperature and humidity can dramatically affect a horse’s health and performance if not managed correctly. High temperature, high humidity, lack of air movement, poor ventilation, dehydration and exposure to direct sunlight all increase the danger of serious heat and sun related problems for humans and horses alike, especially when asked to perform at intense levels.

During exercise, there is a significant increase in the amount of heat produced by working muscles. Muscles cannot transform energy into movement with 100% efficiency. Horses transform energy to movement at approximately 25% efficiency. As a result, some of the energy is lost in the form of heat. The rate of heat production by working muscles is proportional to how hard the muscles work. Therefore the faster a horse goes the more heat it produces. The amount of heat a horse produces in a 99 mile endurance race would be enough to boil approximately 53 gallons of water. That’s approximately 2 gallons per mile. Fortunately for the horse, it is able to dissipate around 97% of the heat it produces during an endurance race in cool-warm conditions!! If not, its body temperature would increase by around 59°F/h. 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. 

Commonly observed signs of heat stress are:

  • Profuse sweating
  • No sweating
  • Rapid breathing rate – panting (>20 breaths / min)
  • Rapid heart rate (>50 beat/min)
  • Skin that is dry and hot
  • Unusually high rectal temperatures (>100°F)

The pinch test

A simple pinch test can basically determine whether a horse is dehydrated as a result of heat stress. When you pinch the horse’s skin on the neck, it should resume its original position immediately. If the skin takes a while to resume to its normal position it could be assumed that the horse is somewhat dehydrated.

Should I work My Horse Today?

A practical test to determine whether it is safe to work your horse 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”. Most riding activities involving long or intense exercise should be postponed when the ambient temperature in degrees Fahrenheit and the relative humidity approach 180.

How does a horse chill out?

The single most important means the horse has for getting rid of the enormous heat load generated during exercise is evaporation. This accounts for approximately 65% of the heat dissipation. Sweat is evaporated off of the skin surface and cools the horse. The lungs account for approximately another 25%. The capacity of the respiratory tract to dissipate heat from the body becomes very important under conditions of high humidity and high temperature when evaporative conditions are not favourable.

High humidity makes evaporative cooling less efficient. The combination of high temperature and high humidity combined can lead to serious trouble quickly. Direct sunshine on a clear day intensifies the problem.

What to do?

Hose horses with cold water. Hose the horse down then take it for a 1-minute walk, then repeat hosing. This will encourage the dilation of capillaries close to the skin, which will increase the evaporation of heat from the horse.

Encourage horses to drink cool water (small amounts frequently). If you are able to monitor the amount of water your horse drinks it will give you a good idea of how much water it is consuming. Horses working in hot/humid conditions should drink approximately 13-18 gallons of water per day.

In severe cases vets have been known to give cold-water enemas or drenches to cool the horses core body temperature down to approximately 100°C.

Supplement electrolytes daily. 2.1 oz of HYGAIN® REGAIN® and 2.1 oz of Salt.

It is important not to overlook cool-down periods following exercise bouts, even when environmental temperatures are well within normal parameters.

Ensure that the horse has plenty of ventilation and access to a cool breeze as convection helps cool horses quicker. If none is available fans/air conditioners can be used to produce an artificial breeze.