Early signs that a dog may be in heat are a red discharge from the vulva, licking that is excessive, changes in behavior or appetite and an increase in temperature. The beginning phase of a dog’s heat cycle is called proestrus.
Spotting or red discharge from the vulva is an early indication that the uterine lining is changing. One way to check for spotting is to wipe the vulva with a tissue. If it appears red, pink or yellow, it may indicate that the heat cycle is beginning. A dog in heat may lick the genital area excessively to rid itself of any discharge. Spotting on the floor may also indicate the heat cycle has begun.
Some dogs exhibit noticeable changes in behavior and have increased restlessness or become less active. Typically, a heat cycle will make a female dog attractive to males who are interested in mating. Females may display signs of aggression if they are unwilling to breed.
Most females will have an increased appetite during heat, because the heat cycle requires more energy. There may also be a rise in body temperature.
As the heat cycle progresses, a female dog usually becomes more receptive to mating. She may display anxious behavior such as barking, howling and sleep disorders.