Taking Your Horse’s Temperature

Written by Sue Stuska, Ed.D.

The first sign your horse is sick is probably that he’s not cleaned up his grain. Your decision to call the vet, and your vet’s response, will be determined in part by the horse’s temperature. Don’t wait for an emergency; prepare now. It’s helpful to know your horse’s baseline temperature at different times of the day and in both hot and cold weather.

Get a thermometer if you don’t already have a thermometer in your first-aid kit. Get one at your first opportunity. Your local farm supply store may carry them; you can order them from catalogs; or your vet may supply them. A traditional glass-and-mercury large animal thermometer with a plastic case should cost around seven to ten dollars. It is cheaper than the fancy battery-run digital readouts and there are no batteries to go dead just when you need them. Store it in a moderate temperature

Prepare the thermometer by tying a string to the eye. Make a hole (using a heated nail) in the end of the lower part of the case for the string to go through—this gives you an easier way to keep track of the lower end of the case and lets you use a more substantial string than would fit inside the case. Thread the string through the case. Tie a clothespin or clip to the other end of the string. This string and clip will save you countless hours of trauma spent looking for a lost thermometer, the danger of the thermometer getting broken or stepped on, and gives you an additional handhold when shaking down the mercury.
Prepare your horse by inserting a latex-gloved lubricated finger in his anus. Lubricate with KY jelly, Vaseline (it’s messier) or saliva (if you can spit accurately!). Be safe and stand beside his hip. He’s likely to clamp his tail as an initial reaction and you want to train through this rather than have him learn the first time that the end of the thermometer may poke him in the underside of the tail.

Shake down the thermometer to well below 100 degrees by grasping the thermometer by the eye end and snapping your wrist repeatedly. This technique may take some time to perfect; hold the string, too, so you won’t drop the thermometer, and persevere until the mercury moves down into the bowl.

Read the thermometer for temperature. The easiest way to find the mercury line is to rest the lower end of the thermometer on the first finger of your other hand (don’t hold the tip or you’ll influence the reading) and roll the thermometer slowly toward or away from you until you can see the silver mercury column.

Insert the lubricated thermometer at least a few inches, and as much as all the way, into the anus. It will slide in more easily if you point it in a slightly upwards direction. Clip the string to the tail hairs. With the string attached, you don’t have to worry about the thermometer going in too far to find. (It would come out in the next bowel movement—and you’d need to be there to find it before it got stepped on.) If the horse pushes it out, you’ll find it hanging from his tail.

Take the reading after at least three minutes. Since you have the string, you don’t have to hold or watch the thermometer; go about your routine. If the thermometer is dirty and a suitable wipe is not available, wrap the thermometer in some tail hairs and pull it through to remove any manure. After you read it, you can disinfect it with alcohol if you want. Normal is 100.5 plus or minus one degree (99.5 through 101.5). A temperature of 102 requires intervention, and 104 degrees or higher is serious. Check with your vet for instructions.

This article originally appeared in Eclectic Horseman Issue No.4