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How do I know when my dog is in heat

A female dog, (also known as a bitch) who is ‘on heat’ is a dog having a menstrual period. The time leading up to the ‘dog period’ is known as a dog heat cycle. Only un-spayed female dogs can come into heat, happening when they are getting ready to mate.

Most bitches will have a dog heat cycle every 6-8 months, although this can vary, depending on breed, size, and age. A ‘dog period’ lasts between 18-21 days. The dog heat cycle starts at different ages, depending on the size of your dog. Smaller toy breeds may start their dog period from four months, whereas larger breeds can be two years old before it begins.

So, what happens during the dog heat cycle? 

There are four stages in a dog heat cycle:


This is when your bitch begins to attract male dogs, even though she may not be ready to mate at this point. This stage will probably last about 9 days, and you may notice some bloody vaginal discharge and swelling in the vulva.


At this point, your bitch is happier to accept male advances and is ready to mate. The vulva is still larger than normal, but the discharge will become lighter in colour and volume. The estrus stage can last for a few days or up to 11 days.


This is the end of the cycle (around day 14), and your dog is no longer interested in mating. The swelling and discharge should now be finished.


The 6-8 months between each dog heat cycle is known as anestrus, and you won’t notice any hormonal changes. Your dog will not be interested in mating during this time and cannot get pregnant.

How can I tell if my dog is in heat?

As well as physical signs of your dog’s heat cycle beginning, there may be behavioural changes. Physical signs to look out for are:

  • Licking and cleaning of the genital area
  • Swelling of the vulva
  • Urinating more frequently than usual
  • A bloody or straw-coloured discharge
  • The tail being held low, close to their bodies

A female dog in heat behaviour will also change. You may notice they have an interest in male dogs, and they are more receptive to their advances. Your dog’s personality could be different, just like it can be in humans. They may become more aggressive, nervous, or anxious and clingy to their owners.

During your dog’s heat cycle, you will have to be very careful not to let her mate unless you are planning to have a litter of puppies. Male dogs can be quite persistent in getting to your dog as she will be emitting breeding pheromones. It is worth considering walking your dog in quiet areas away from others and keeping her on a lead during her cycle. 

It can be quite an unsettling experience for dogs and owners, so unless you plan on breeding from your bitch it is worth considering having them spayed. You can discuss this process with your vet. 

If you have an Agria Pet Insurance policy, you can access the Agria Vet Guide app for free advice at any time.


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