How Long Does a Dog's Heat Cycle Last?

Dog laying on carpet and holding stuffed dog toy
Les Hirondelles Photography / Getty Images

Although animals seem to still retain their instincts in regards to breeding, that is not always the case. Occasionally, they need help from their human caretakers if a problem arises, such as a uterine infection, difficult pregnancy, or problems giving birth. Be prepared for any issues by learning about the four stages of your dog’s heat cycle.

What Are the Four Stages of the Canine Heat Cycle?

During your dog’s complete heat cycle, she will experience four phases. A typical heat period lasts roughly two to four weeks, with a pregnancy or resting phase following the estrus period. Knowing what to expect will help prepare you and your dog for any abnormal behaviors or problems during her heat cycle. As your pooch progresses through her cycle, you will notice these four stages:

  1. Proestrus: Proestrus is the start of the heat period where your dog’s body is preparing to mate and averages about nine days, but can last from three to 17 days. Her vulva will swell and you may notice a blood-tinged discharge, but many dogs are fastidious about messes and will clean themselves before you notice. Your dog may also hold her tail close to her body and stick just as close to your side, displaying clingy behavior. At this stage of the heat cycle, your dog will attract males, but she will not be receptive to them and may become aggressive if they try to mount her.
  2. Estrus: The estrus phase is the mating phase and usually lasts around nine days, but can be as short as three or as long as 21 days. During this time, blood flow will lessen and then stop, but the discharge may change to a straw color. Female dogs will attract and accept males, with ovulation occurring two to three days after mating. You may notice your dog urinating more frequently and marking spots within and outside your home to spread pheromone messages indicating her readiness to breed. If an intact male is present, your female dog is likely to present herself to him, hindquarters first, and with her tail held to the side.
  3. Diestrus: This phase occurs directly after the “in heat” stage and lasts for about two months. Her body will proceed with the pregnancy or return to rest, as her vulva returns to normal size and the vaginal discharge disappears.
  4. Anestrus: Anestrus is the uterine repair phase, in which no sexual or hormonal behavior is present, and can last for anywhere from 90 to 150 days before the next proestrus stage begins.
Illustration of the heat cycle stages in dogs including proestrus, estrus, metestrus, and anestrus.
The Spruce / Melissa Ling

How to Prevent Your Dog From Going Into Heat

The only option to prevent your dog from going into heat is to have her spayed. Spaying is highly recommended for all female dogs unless you plan on strengthening the breed. Once your dog is spayed, she will have a reduced risk for mammary cancer and will be unable to contract uterine infections or go through a heat cycle.

You can have your dog spayed while she is going through her heat, but the surgery is more complex. Speak with your veterinarian about the best time to spay your pet.

General "Rules of Thumb" for Your Dog’s Heat Cycle

  • The age at which a dog experiences her first estrus varies greatly between breeds. Toy and small breeds mature much earlier than giant breeds and can come into heat as early as four months of age. Giant breeds may be two years old before they experience their first heat.
  • On average, a female dog will come into her first heat between six and 15 months of age.
  • Most dogs have two estrous cycles per year.
  • Male dogs will be attracted to a female dog entering her heat cycle before she is receptive. Watch for defensive aggression that warns males to back off.
  • Remember—just because your dog is no longer bleeding, does not mean she can no longer get pregnant. She’s much more likely to let a male mate immediately after the bloody discharge stops.
  • Dogs can get pregnant during their first heat cycle, but this is not advisable as a six-month-old dog is not yet fully grown/mature, and complications for the mother and the puppies are more likely.
  • Ideally, a female dog should have two normal heat cycles before being bred.
  • To prevent a possible pregnancy while your dog is in heat, keep her separated from male dogs for at least three to four weeks after the first sign of bleeding.
If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
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  1. Estrous Cycles In DogsVCA Animal Hospitals

  2. Canine Estrous CycleEast Central Veterinary Hospital, 2020

  3. Spaying And NeuteringAmerican Veterinary Medical Association