Bob Judd, DVM, DABVP (Equine Medicine), DABVP (Canine and Feline Practice)
A horse’s temperature usually ranges from 99.5 to 101.5 degrees Fahrenheit. However, each horse has a temperature that is normal for that horse, so it’s a good idea to routinely check your horse’s temperature with a human rectal thermometer to know the normal range.
If your horse’s temperature is always around 99.5 to 100, and you get a reading of 101.5, this is probably an increase. Dr. Joan Norton, VMD, Dipl. ACVIM indicates in the publication The Horse that it is important to check your horse’s temperature at least daily, especially if your horse travels to shows or is stabled at a barn with lots of different horses coming and going. First, you need to find out if the increase in temperature is a fever or caused by another issue.
Your horse’s temperature can increase by having a high body temperature or a true fever. The brain has a set point to control temperature and sensors in the body will determine an increase. This will trigger actions like sweating to preserve the set point. Otherwise, a horse’s temperature would remain extremely high due to environmental temperature or from exercise.
With hyperthermia, the body temperature rises but the set point does not so the horse is simply overheating. This can be due to exercise, a lack of sweating, or certain drugs or toxins. With high-intensity exercise, muscles produce more heat than the body can disperse, and your horse’s temperature rises. After exercise, the temperature should return to normal once your horse has cooled out. With a true fever, the set point increases, and this is due to infection or inflammation somewhere in the body. If your horse has a persistent fever, a call to your veterinarian is in order.