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Call the vet if your horse's temperature remains high. Call the vet if your horse has other symptoms. Call the vet if the thermometer slips internally.
If you have taken your horse's temperature a few times over the course of several hours or a few days, and it remains high, call the vet. Call your vet if the horse's temperature remains above 101.5 degrees Fahrenheit. If your horse's temperature is above the normal range, and he has other symptoms, contact your veterinarian. Observe your horse and keep track of the other symptoms, such as loss of appetite or lack of energy. It is possible that the thermometer may slip entirely into the horse's rectum. If this happens, call your veterinarian immediately. If the worst did happen and the thermometer slips internally, there is a chance it may be passed when the horse has a bowel movement. Call your veterinarian immediately, but monitor fecal output and check for the presence of the thermometer in the droppings. You can always cancel a vet visit if the thermometer comes out on its own.