Fever (an increase in core body temperature) in pets can be the body’s response to anxiety, heat stress, shock, infectious diseases, drugs, poisons, and serious underlying medical problems. Therefore, it is important to have your pet checked right away if you suspect he or she is running a fever. Normal body temperature for cats is 100.5-102.5℉ (38.1-39.2℃). Your pet’s body temperature is measured by taking a rectal temperature. A digital thermometer is easiest, but a glass one will work as well.