Heat stress in horses

When summer temperatures soar, caution and common sense must be used if or when exercising your horse to avoid heat stress.

It is well known that horses sweat to regulate body heat. Hot weather can limit a horse’s ability to dissipate heat from the body. In some cases, temperature with the combination of humidity can make the evaporative cooling effect of sweating less efficient. A horse may experience heat stress when internal heat continues to rise once the sweating mechanism can no longer keep up with getting rid of body heat.

General guidelines in determining the danger levels of heat stress in horses:

Table 1: Veterinary Manual for the Performance Horse (Loving, 1993.)

 Temperature plus Humidity


 < 120

Normal cooling mechanisms are sufficient if the horse is not obese or has a long hair coat.

 >   140

Horse relies mostly on sweating to dissipate body heat

 > 150

If  humidity contributes to more than half, sweating becomes compromised

 > 180

Heat stress may occur, no natural means for the body to rid heat and internal temperature may continue to rise

It is important to realize that cooling down an overheated horse too rapidly can shock the horses system.

Cooling method considerations:

  • Walking and natural cooling works best to dissipate heat from muscles
  • Cool water application – soaking the neck, chest and legs will create the same effect as sweating to dissipate internal body heat
  • Avoid applying water to large muscles in the back and hindquarters of an overheated horse to prevent the horse from tying-up.

Typically, heat stress in horses develops from overexertion leading to overheating. Hot weather is not the only reason a horse may be susceptible to heat stress. Riding a horse beyond its level of conditioning also produces excess body heat. Therefore, it becomes the responsibility of the horse’s caretaker to know how well conditioned the horse is and the caretaker’s proficiency at interpreting distress in the horse when managing horses during periods of hot weather and/or exercise.

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