How do male dogs know when a female is in heat?
A male dog is able to tell when a female dog is in heat because of the scent that a female gives off when she is in the heat cycle. When a female dog is ovulating, she will go through the four stages of her heat cycle. Female dogs normally have two heats per year, and are particularly fertile during these heats.
During the Proestrus Stage, which can last up to 20 days, female dog will have a swollen vulva, colored discharge and begin having a distinct smell that will attract male dogs. During the Estrus Stage, which lasts one to two weeks, the female dog will be fertile and eager to breed. The scent during this stage is also the highest, which attracts many more male dogs. A female dog will be willing and eager to mate with a male dog during the Estrus Stage.
During the Diestrus Stage and the Anestrus Stage, a female dog’s bleeding slows down and she returns back to her normal behavior. The scent will begin to wear off and male dogs will not be as attracted to the female dog.