Heat Stress in Horses

Jennifer Rice, DVM
Written by:
Published: March 28, 2022
Heat Stress in Horses

What Is Heat Stress in Horses?

Heat stress and heat stroke are equine emergencies that are most commonly observed in the summer months when the temperature and humidity outside are at their highest.

Horses naturally produce heat in two normal metabolic functions: digestion and exercise. Heat stress occurs when there is a breakdown in the way a horse normally cools down and sweat is not able to evaporate and allow for proper cooling. If left untreated, the process of heat stress can lead to heat stroke, which can be life-threatening.

Symptoms of Heat Stress

A horse who is experiencing heat stress may exhibit one or more of the following signs:

  • Profuse sweating or less sweating than expected

  • Hot skin to the touch

  • Rapid breathing

  • Rapid Heart rate or pulse that does not improve with rest from exercise

  • Increased body temperature of above 102 degrees Fahrenheit

  • Muscle weakness

  • Stumbling

  • Dehydration (signs may include tacky mucous membranes, sunken eyes, lack of skin elasticity or tent when you pull up from body, lack of urination)

Symptoms of Heat Stroke

Heat stress can quickly turn into heat stroke. Symptoms of heat stroke include:

  • Rapid respiratory rate continues

  • Increased body temperature of over 106 degrees Fahrenheit

  • Collapse

  • Convulsion

Causes of Heat Stress and Heat Stroke in Horses

There are several factors and conditions that can lead to heat stress in horses.

These conditions include:

  • High outside temperature

  • High environmental humidity

  • Poor barn ventilation

  • Prolonged exposure to sunlight

  • Excessive work

  • Transportation

  • Obesity

The most common scenario for a horse to become heat stressed is if they are exercised when the conditions outside are hot and humid. Under these conditions, evaporation from sweat is greatly reduced and heat stress leading to heat stroke are much more likely to occur.

What Temperature Is Too Hot to Ride a Horse?

Every horse tolerates heat differently, but there are some general guidelines. In the heat of summer, it is best to ride in the mornings and evenings instead of the heat of the day. It is also important to allow adequate time for a horse to acclimate to hotter weather if they are new to the environment. Below is a chart with guidelines on when it is too hot to ride based on the outside temperature and humidity.

Outside temperature (F) + Humidity (%)

Heat risk with exercise

Less than a 130

Minimal risk

130-150

Low risk, as long as horse replenishes fluid loss from sweating

Greater than 150

Moderate risk of heat stress

Greater than 180

Severe risk, DO NOT EXERCISE

Additional factors that can make a horse more prone to heat stress include:

  • Dehydration

  • Loss of electrolytes from sweat

  • Geriatric horses

  • Horses with anhidrosis (unable to sweat normally)

How Veterinarians Diagnose Heat Stroke in Horses

Your veterinarian will start with a history and physical exam in order to diagnose heat stress and heat stroke in your horse. During the exam, it will be important for the veterinarian to look at the horse's mucus membranes for color and moisture, check heart and respiratory rate, and check body temperature.

Treatment of Heat Stroke in Horses

Treatment of heat stress and stroke in horses will depend on the severity of your horse’s symptoms. If you suspect your horse is experiencing heat stress, it is critical to stop all exercise immediately and move your horse to a cooler setting, such as in the shade. Be sure to contact your veterinarian immediately.

While waiting for veterinary assistance, place a fan next to your horse and spray them with cool water. Allow your horse access to fresh water in small intervals until the veterinarian arrives. Your veterinarian will likely want to give your horse some intravenous fluids and electrolytes to help cool them off as well as replenish fluid and electrolyte losses.

Recovery and Management of Heat Stroke in Horses

Horses generally recover from heat stress with no lasting effects. Depending on the severity of the heat stress, your veterinarian will be able to advise you on how to safely return to your horse's normal lifestyle. Typically, allowing rest for a day or two and slowly easing your horse back to exercise is advised.

Prevention of Heat Stress in Horses

You can help prevent heat stress in your horse in a variety of ways:

  • Provide access to fresh water

  • Provide access to shade

  • Reduce ride time and intensity when it is hot and humid

  • Ride in the morning or evening when it is the coolest

  • Ask your veterinarian about providing electrolytes in times of strenuous work and increased sweating

  • Provide access to a fan if there is low to no air flow in your horse’s stall

  • Consider clipping horses with long hair

  • Transport horses during the cooler parts of the day

Heat Stress in Horses FAQs

How does a horse normally cool off?

Heat stress occurs when the body's normal mechanisms to cool off are not able to function sufficiently to disperse heat. Normally, a horse can get rid of extra heat through sweating and exhaling of warm air. By sweating, the horse becomes wet and allows for evaporation to take place, which cools down the horse.

How do you cool down a horse after exercise?

It is always important to take the time to cool out your horse at the end of every ride. This is crucial not only for the horse to appropriately cool down but also for the well-being of your horse's heart, lungs, and muscular system. Ten to fifteen minutes of walking at the end of every ride allows a chance for your horse to cool down slowly. After you have finished walking out and have unsaddled, always offer fresh water. Hose off your horse with cool water when sweaty and provide access to a fan after exercise.

Featured Image: iStock.com/kertu_ee


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