How To Tell If Your Dog Is Into Heat (Estrus)

When Do Dogs Become Pregnant?

A female dog is said to be "in heat" when she is ovulating, ready to breed and get pregnant. Dogs can go into heat as early as 6 to 8 months of age, so if they do and have sex with a male dog when they are in heat, they may become pregnant even though they are still growing.

Pet parents sometimes miss the first heat cycle, therefore many veterinarians recommend spaying the animal at 6 months of age to prevent unintended pregnancies. Depending on the dog's age, size, and breed, different heat cycles occur. Giant breeds may cycle every three to four months, medium and big breeds commonly every six months, and small dog types every three to four months. Older dog will cycle less often. 

What is Happening When a Dog is in Heat? There are 4 stages, or heat periods, in a dog’s heat cycle: proestrus, estrus, diestrus, and anestrus. Proestrus is the stage that many people recognize the signs of a dog in heat. Proestrus typically lasts around 7 days. During proestrus, male dogs are attracted to a female, but she is not receptive to them. In proestrus, there is swelling of the vulva and usually bloody vulvar discharge. Estrus is the next stage, and it is during this estrus phase that a female dog is fertile and accepts a male dog’s advances. Estrus typically lasts 9 days. The vulva is still swollen, though maybe less so, and there is less bloody discharge. Diestrus lasts around 8 weeks, and the female is no longer fertile or receptive to males. During this time, the vulva returns to normal size and discharge dries up. Anestrus defines the time period between diestrus and proestrus. Anestrus lasts around 3-5 months depending on the size and age of the dog. Your dog’s body is resting at this time and preparing for the next heat cycle. Signs of a Dog in Heat There are behavioral clues and physical symptoms of a dog in heat, which can include: swollen vulva and bloody vaginal discharge increased moodiness, growling at humans or picking fights with other dogs in the household, especially other unspayed female dogs decreased or increased interest in human interactions increased interest in roaming or getting out of the yard cutting a hole for her tail.