A normal healthy dog has a body temperature of 101-102.5°F (or 38.3-39.2°C). If your dog’s temperature is higher than this range, they likely have a fever.
A fever (pyrexia) occurs as the body’s response to any number of disease processes; this includes infections, inflammation, and even some cancers.
Dogs with a true fever are usually feeling sick. The most common symptoms include lethargy and decreased appetite. Febrile dogs may tremble/shiver, and prefer to lie on cool tile or hardwood rather than carpets and bedding. Depending on the cause, vomiting and/or diarrhea may occur. There could also be coughing or nasal discharge.
A fever should never be diagnosed purely based on how a dog feels to the touch — a thermometer is the only way to accurately determine this.
A well lubricated rectal thermometer, inserted approximately 1 inch into the rectum will provide the most accurate temperature measurement. That being said, owners should be cautious doing this at home as most dogs are not a big fan of having this done. If your dog is feeling well, there’s no reason to check their temperature. If they’re feeling sick, they should get checked by they veterinarian anyway, so you can leave this fun job to them!
Note: a fever should not be confused with hyperthermia, which occurs when a dog becomes overheated due to external temperatures being too high, or due to overexertion.