How Long Does a Dog's Heat Cycle Last?

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Non-spayed female dogs will normally go into "heat" or estrus twice a year. The age at which their cycles start and the duration of the cycle vary greatly between the breeds of dogs and individual dogs but in general, dogs come into heat about twice a year. If you are planning to breed your dog then you'll need to learn her estrus cycle in order to make the most efficient use of breeding time. If you do not intend to breed your dog, it's important to consider spaying her. This will ensure no unwanted puppies and will end the estrus cycle in your dog. If you do intend to breed your dog, here's what you need to know. 

The Four Stages of the Canine Estrus Cycle

Illustration of the heat cycle stages in dogs including proestrus, estrus, metestrus, and anestrus.
 Illustration: Melissa Ling. © The Spruce, 2019

Proestrus: vaginal discharge, males attracted to females, females unwilling to mate. Length: 4-20 days.
Estrus: swollen vulva, yellowish vaginal discharge, mating occurs during this phase. Length: 5-13 days.
Metestrus (or Diestrus): the period after estrus or mating. Length: 60-90 days. If pregnant, pregnancy lasts between 60-64 days in the dog.
Anestrus: the period of inactivity (sexual and hormonal) between estrus phases. Length: 2-3 months.

General "Rules of Thumb" for Canine Estrus

  • The first estrus cycle occurs at puberty, which usually occurs by age 6-12 months; for some small breeds, as early as 5 months, and for some large and giant breeds, the first cycle may not occur until 14 months of age or older.
  • On average, dogs have two cycles a year.
  • The estrus cycle lasts on average 12-21 days, but maybe be as short as a few days to four weeks. The estrus period length varies widely between breeds and individual dogs.
  • The length of a cycle varies widely, even for dogs of the same breed. If in doubt, assume the longer end of the range for the cycle length.
  • Bleeding occurs prior to a female being receptive to a male (allowing mounting by the male), but male dogs will be very attracted to the female in the proestrus stage.
  • Dogs can get pregnant during their first heat cycle, but this is not advisable as a 6-month old dog is not yet fully grown/mature, and complications for the mother and the puppies are more likely.

For dogs that are meant to be house pets, it has traditionally been recommended to spay them before the first heat, eliminating the risk of accidental pregnancy and reproductive diseases later on in life.

Recent studies indicate that early spaying and neutering (referred to simply as "neutering" for both genders) may have adverse health effects later on. Early neutering and effects on health is a complicated issue. Make sure to speak to your vet about any questions you may have regarding your pet's health. 

Dogs may be spayed while in heat (or pregnant), but there is an additional risk of bleeding due to the engorged vessels and tissue of the reproductive tract. The cost of surgery while in heat or pregnant is often higher as well because of this added risk.

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.