Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Summer Heat Could Hurt Your Horse


Pet Column for the week of June 25, 2001


Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Jennifer Stone
Information Specialist

Everyone finds the high temperatures of summer bothersome-even horses! Strenuous exercise in hot, humid weather can spell trouble for some horses, so owners should learn how to handle heat-related problems.

Dr. R. Dean Scoggins, equine Extension veterinarian at the University of Illinois College of Veterinary Medicine in Urbana, says, "The most serious heat-related problem seen in horses is anhidrosis, which is the inability to sweat." When horses work hard in hot, humid conditions, the sweat glands can become overtaxed and unable to excrete fluids. Sweating is the body's primary means of getting rid of extra body heat, and when an animal is unable to sweat its temperature can rise to dangerous levels. This problem is not often seen in draft horses, but is common in thoroughbreds, Arabian horses, quarter horses, race horses and trail horses.

The normal temperature for a horse is 100 degrees Fahrenheit. When its temperature reaches 104 or 105 degrees Fahrenheit, the horse is considered to have heat stroke, which is an accumulation of body heat due to a failure of the body's cooling mechanisms. When its temperature reaches 107 or 108 degrees Fahrenheit, neurological damage or death can occur.

Owners who work their horses hard in the summer should consider carrying a thermometer so they can take their horse's temperature if they suspect overheating. Horses that are overweight and are not in good shape are more prone to this problem because extra layers of fat tend to retain heat.

The first sign of heat stroke is that sweating stops. Under normal circumstances, the body of a horse that is working hard should be covered with sweat. When anhidrosis occurs, there may be some sweat on the sides of the neck and between the legs from friction, but the rest of the body will be dry. Horses who are suffering from this problem will breath more heavily than normal, and although their bodies are not designed to breath through their mouths, they may try to do so.

If you notice these signs, stop all activity and contact your veterinarian. Then try to get the horse's temperature back down to normal. To do this, you can get the horse to a fan and pour cool water over the body, especially around the head and neck and on the inside of the legs, where the large blood vessels are located. By cooling the blood flowing though these areas, you can bring down the overall body temperature.

Dr. Scoggins says, "Research done at the University of Illinois College of Veterinary Medicine found that even ice water could be used to cool the horse with no detrimental effects."

After heat stroke has occurred, it is necessary to allow the horse to rest for a couple of weeks before returning it to work. When work is resumed, its duration and intensity should be reintroduced gradually until the horse is back to its normal workload.

Foals, particularly those under 30 days of age, are very susceptible to overheating because their heat regulatory system has not fully developed. They may get overheated from too much physical activity in hot, humid weather. Dr. Scoggins advises, "If you put a mare and foal out to pasture, leave them for less than an hour and observe them. If the mare starts running along the fence with the foal in pursuit, catch her and put her back in her stall."

To prevent overheating, put horses out to pasture when it is cooler early in the morning and in the evening. If leaving the horse outside during the hottest part of the day is unavoidable, then shade is critical. Air movement is also very important. Shade from a shed wall is not as good as the shade of a tree or a roof on posts. Dr. Scoggins says, "Good air movement can reduce the temperature in the shade by as much as 10 to 15 degrees." A salt and mineral mix can help replace important electrolytes that are lost due to excessive sweating. Finally, make sure that fresh water is available at all times. If water smells sour, the horse will probably not drink it.

The best way to prevent heat related problems is to watch your horse for signs of overheating and anhidrosis. If you think that your horse may be suffering from a heat-related problem, contact your local equine veterinarian.