When do dogs go into heat?

A dog that is not spayed first enters heat when she is between 6 months old and 24 months old. If she is spayed, she normally experiences heat twice a year. Smaller dog breeds typically experience heat earlier than larger breeds. Heat lasts about 18 days.

At the beginning of a heat cycle, a dog's vaginal discharge contains blood. Later in the cycle, when the dog is ready to breed, the discharge reduces and becomes more of a straw color. During heat, a dog may urinate more frequently than usual. A dog can be spayed when she is 2 months old, although it depends on the breed.