By Ben Espy, DVM, DACT
Question: What’s a normal temperature for a horse, and how do I take it?
A. For an adult horse, any body temperature at or below 101.5 F is considered normal. Just like humans, equines thermoregulate, which means their bodies maintain a constant internal temperature, regardless of the temperature of the surrounding environment. Individual horses’ normal temperatures may vary, but we only worry about them getting too low when horses are sick enough to be in circulatory or septic shock. In horses that appear healthy otherwise, there’s no such thing as a temperature that’s too low.
Readings above 101.5 degrees, on the other hand, are cause for concern. Strenuous exercise can raise your horse’s body temperature by a few degrees, but that should return to normal within 90 minutes of finishing the exercise. If it remains elevated for longer than that, he may be dealing with an underlying illness or he may suffer from anhidrosis, a condition in which horses lose the ability to cool themselves by sweating.
Temperature-taking is vital for good equine husbandry, so all horses should learn to stand quietly for the procedure from an early age. It is completely painless, and almost all horses tolerate it easily. However, it can be extremely dangerous for the human handler to attempt doing it with an uncooperative horse, such as a misbehaving yearling. When in doubt, ask one or more experienced horsepeople to help you get the job done.
To measure your horse’s temperature, use a plastic or digital “oral” or “rectal” thermometer. Oral and rectal thermometers are essentially the same thing. Digital thermometers are safer (harder to break and mercury-free) than glass ones, and so much faster that you don’t need to resort to the old, occasionally unreliable method of clipping the thermometer to the horse’s tail while you wait for the temperature to register. The least expensive models read in about 30 seconds, whereas slightly more expensive models read within 10 seconds.
Take a baseline reading at a time when your horse is relaxed, such as during a meal. If he is young, does not stand tied or you don’t know him well, ask a friend to hold him while you take his temperature. If you are on your own, tie him up. (Holding his lead rope while taking his temperature makes it too easy for him to spin in a circle to avoid you.)
Stand next to your horse’s hind leg, facing the direction of his tail, close enough for your shoulder or side to be in contact with him so you’ll sense any motion in his body if he begins to get antsy. If you are right-handed, stand on his left side, with the thermometer in your right hand; if you’re left-handed, stand on his right side, with the thermometer in your left hand. Throughout the procedure, be careful not to turn your body to face his leg, as this puts you in a very vulnerable position — your knees won’t be free to bend if he kicks or moves suddenly in your direction.
Next, place your arm closest to the horse across his croup and gently grasp the top of his tail in your hand. Raise it up high enough to give your other hand access to the anus. If your horse is young or you’re not sure how he reacts to thermometers, gently touch the skin around the outside of the anus with the thermometer before inserting it. This will help to accustom him to the feel of it. Then guide the end of the thermometer into the rectum, pressing it several inches inside, leaving the digital screen outside the body so you can see it while it registers the temperature.
Continue holding the tail and the end of the thermometer firmly until the final reading is clear (consult the manual that comes with the thermometer ahead of time to see exactly how your particular brand indicates this). Then gently remove the thermometer and double-check the reading.
Use this baseline temperature for comparison when your horse shows signs of stress or illness. If his temperature goes above normal, consult your veterinarian. In some cases, depending on the cause of the fever, your vet may be able to prescribe a fever-reducing medication, such as Banamine or phenylbutazone (bute), over the phone. However, because spiking a temperature of 105 degrees or higher, whether due to exercise or illness, can lead to serious secondary problems, such as laminitis or colitis, immediate veterinary care is recommended. (Note: Like human children, foals have slightly higher normal and febrile temperatures than adults. Their baseline temperatures can run up to about 102 degrees, and they can spike fevers as high as 106.)
Meanwhile, keep your horse up-to-date on his vaccinations for influenza (flu) and equine herpesvirus, also known as rhinopneumonitis or “rhino,” especially if you trailer him to lessons and competitions frequently. Flu/rhino viruses are the number-one cause of elevated temperatures in adult horses.
A specialist in equine reproduction and infertility, Dr. Benjamin Espy has practiced veterinary medicine in Texas and Kentucky. Board certified in equine reproduction and licensed to practice acupuncture, he is the chairman of the American Association of Equine Practitioners Owner Education Committee and serves on the AAEP Board of Directors and the Board of Directors for the American College of Theriogenology (www.theriogenology.org). Dr. Espy is also the liaison for the Texas Equine Veterinary Association and is a veterinarian for the Professional Rodeo Cowboys Association during the San Antonio Stock Show and Rodeo.
This article originally appeared in an issue of Practical Horseman magazine. Reprinted with permission.
Reviewed by original author in 2016.