Basics of The Dog’s Heat Cycle

Basics of The Dog’s Heat Cycle

October 19, 2021

When you are familiar with your dog’s heat cycle, it is easier for you to prepare for her physical and behavioral changes and support successful mating – or prohibit unwanted ones from happening. In this article, we’ll walk you through the basics of the female dog’s reproductive cycle.

Essential numbers in a nutshell

  • The first heat happens on average between 6 and 15 months of age. Rule of thumb says that smaller breeds tend to have their first heat at an earlier age, larger breeds later, but this varies between individuals.
  • Heats appear every 6 months on average. Small breed females may have up to three seasons per year, while it is normal for giant breed females to have their heat only once in a year.
  • The heat cycle will last approximately 21 to 28 days.
  • Female allows mating: for 9 days on average (the estrus stage), but this might vary from 4 days to 24 days.
  • Dog’s pregnancy lasts on average 63 days from ovulation. Again, there are differences between breeds and individuals. Another reason for variation is that exact conception time is difficult to determine – even if we knew when the mating happened: sperm can live several days inside the female. Dog’s eggs might be fertile up to two days. The exact ovulation time can be determined with progesterone test. It helps to calculate the real pregnancy days. 
  • False pregnancy symptoms might appear 4 to 9 weeks after the season.

Dog Heat Cycle

The stages of the female dog's heat cycle. 

The four stages of the canine heat cycle

During the female dog’s heat cycle, you’ll notice four stages. The actual heat – or the season – includes the first two stages. After that, the fertile part of the cycle comes to an end, and the female will be no more receptive to mating.


 1. The Proestrus Stage — Preparing

The average length of the proestrus stage is 9 days but varies from 3 to 17 days.

During the proestrus stage, the female will usually not allow mating, but as an owner, you can see some changes in your dog. The main reason for these changes is the rising estrogen level in the dog’s body. In ovaries, the follicles – where the eggs are later released – are enlarging.

The signs of proestrus stage:

  • Swelling of the vulva – and you may notice some bloody discharge, too.
  • Personality changes: your dog might be more affectionate to you than usual, even clingy. Some dogs act slightly grumpy towards others.
  • Appetite changes.
  • Male dogs are attracted to your dog, but she’s usually not receptive to them.
  • Tail tucking: the dog might tuck her tail between her legs or sit down if another dog approaches.

2. The Estrus Stage — Time to breed

The average length of the estrus stage is 9 days but can range from 4 to 24 days.

Estrus is the stage when the female is receptive to the male – the “actual” heat. During the estrus stage, the fertile period occurs, and the dog can get pregnant. Estrogen levels in her body are dropping, and progesterone levels are increasing. 

The signs of estrus stage:

  • The vaginal discharge is lightening to pinkish or turning brownish – or it can become almost invisible.
  • The vulva is softening and swelling.
  • Personality changes: the dog might be willing to run away to find mating partners.
  • Male dogs are significantly attracted to her: you may have uninvited visitors in your yard.
  • Tail flagging: your dog might ‘flag’ her tail by moving it to the side, making herself available to males.

It’s a common misunderstanding that the dog is fertile only when she’s bleeding. That’s a myth: most female dogs have their most fertile days right after they stop bleeding.

3. The Diestrus Stage — Gestation

Length: 60 to 90 days

At the diestrus stage, your dog is not interested in mating anymore. The signs of heat will go away: there won’t be any discharge anymore, and the vulva shrinks back to its normal size.

Note: Right after the estrus stage, the risk of pyometra, an uterus infection, is at its peak. If you notice a pus-like discharge coming from the dog’s vulva, you should immediately take her to the veterinarian.

This stage is the one that you might start to see signs of pregnancy – or false pregnancy – in your dog. If there is a possibility of pregnancy, you might want to confirm it by testing the dog with the Bellylabs pregnancy test or take her to the vet to get checked.


4. The Anestrus Stage — Recovery

The anestrus stage is the final stage of your dog’s heat cycle, a hormonally initiative one. It is also called the resting stage. Usually, there’s no hormonal or increased sexual behavior present during this stage – until the next proestrus stage begins.

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