Hypothermia can be caused by prolonged exposure to cold temperatures, impaired ability to control body temperature (very young, aged or compromised dogs) or the presence of certain illnesses like hypothyroidism. Newborn pups are not able to properly control their body temperature and will become hypothermic without an external heat source. The normal temperature of an adult dog is 100.5-102.5 degrees F (38-39.5 degrees C). Signs of hypothermia include shivering, lethargy, weakness, depression, stiffness, low heart rate, difficulty breathing, and coma.