ASPCA Logo

How to Tell If Your Dog's In Heat

Estrus, or heat, is the stage in a female dog's reproductive cycle during which she becomes receptive to mating with males. At this time, estrogen levels first increase and then sharply decrease, and mature eggs are released from the ovaries. Ideally, your dog should be spayed before she enters her first heat cycle.

When Does A Dog Experience Her First Estrus?

First estrus generally occurs when an unspayed female dog is between six and 24 months old. It tends to occur earlier for small-breed dogs and later for large-breed dogs.

How Often Do Dogs Go Into Heat?

Although it varies with different breeds and individual dogs, an unspayed female usually goes into heat twice yearly, about every six months.

How Long Does a Dog Stay in Heat?

The time during which male dogs are attracted to a female dog is variable, approximately 18 days. However, females are receptive to males for only about half of this time.

How Can I Tell if My Dog Is In Heat?

During estrus, your female dog may appear nervous, easily distracted and more alert than usual. She may also urinate more often than she normally does. You'll most probably notice changes in her behavior; this is caused by a shift in her hormone balance. When a female dog is ready to be bred, she may initiate sexual interactions with other dogs, elevate her hind quarters toward males when they approach, deflect her tail to one side and tense her rear legs.

At first, vaginal discharge is blood-tinged and the vulva is swollen. When the female is receptive to males, vaginal discharge decreases in amount and is straw-colored.

How Can I Prevent My Dog From Going Into Heat?

It is highly recommended that you get your female dog spayed, not only to prevent estrus and accidental pregnancy, but to protect her against breast cancer and diseases of the reproductive system.