A female dog’s first heat is a big milestone in her life. It’s a part of puberty and a sign that she’s growing up and sexually mature.

If you are not desexing your dog before their first heat, it is a good idea to be prepared for the possibility that she may get pregnant, even if you don’t plan on breeding her and she’s not regularly exposed to other dogs.

The more you know about your dog’s first heat, the better you’ll be able to help her through it.

What is a heat cycle?

A dog’s heat cycle is similar to a human’s menstrual cycle in that it’s a hormonal cycle that prepares their body for pregnancy. But unlike in people, the visible signs of a heat cycle in dogs occur during their fertile period.

When does a female dog experience their first heat cycle?

Most female dogs experience their first heat cycle when they’re 6 to 24 months old, depending on their breed and size. Smaller breeds tend to have their first heat at earlier ages, while larger breeds start at later ages. Smaller breeds can also cycle up to three times per year, whereas larger dogs may only have one heat cycle in a year.

How long does a dog’s heat last and what does it look like?

Most female dogs are “in heat” for about three weeks, but there is a lot of individual variation. The heat cycle is divided into 4 stages.

Early signs of heat

The first, and most noticeable, stage is called proestrus and lasts on average for about 9 days but can last up to 3 weeks. During this stage, your dog may:

  • have a swollen vulva and bloody discharge
  • urinate or mark more than usual
  • attract male dogs
  • be nervous or restless
  • eat less

Most dogs are quite good at keeping themselves clean, but you can consider using dog diapers, pads, or covers to protect your home if your dog spends a lot of time inside.

You should also keep your dog away from entire (non-desexed) male dogs. Most females will be snappy and reject any attempts at mating, but some will allow mating at any time during their cycle. Sperm can survive in the reproductive tract for up to a week, so there is a chance she could get pregnant if mated during this stage.

The fertile window

The second stage of heat is called oestrus. It also lasts on average for about 9 days but can last up to 3 weeks. This is the fertile period when she can get pregnant.

During this stage, you may see these changes in your dog:

  • Less or clear vulval discharge
  • Smaller and softer vulva
  • More interest in male dogs
  • She may lift her tail to the side
  • She may stand still or move her legs when mounted by a male dog

These signs mean that your dog is ready to mate.

Breeding dogs is a big responsibility that needs a lot of planning, preparation, and care. If you don’t want puppies, be very careful and avoid contact with male dogs at all costs for the entire duration of your dog’s heat.

Keep your female dog indoors or in a secure area. Be aware that entire male dogs can smell a female dog in heat from kilometres away and will seek them out. They may jump very high fences, or even mate through the fence.

Some desexed male dogs will also try mounting a female dog in season, so it may be best to separate her from them as well. Female dogs may also mount other females during their heat cycle.

The high progesterone stage

The third stage of the dog heat cycle is called dioestrus, and their hormones (namely, progesterone) will remain high whether they were mated or not.

This is why there can be external signs of pregnancy, even if the dog is not pregnant. This is called a pseudopregnancy, and can include symptoms such as mammary enlargement, lactation, being off food, or nesting. The vulva and uterus will remain permanently larger than it was before the heat.

This stage of the heat cycle lasts for about 8 weeks.

What should you do once your dog is out of heat?

Between heat cycles, a female dog will have a resting period called anoestrus.  This resting phase can last for several months until the next heat cycle begins.

If your dog was bred during the oestrus stage, you should take her to the vet to confirm her pregnancy and monitor her health. Please call your local Greencross Vet to discuss timing of this visit.

If your dog was not bred during the oestrus stage, you should consider desexing her to prevent unwanted pregnancies and future heat cycles, which can increase your dog’s chances of developing health problems like uterine infection and mammary cancer. You should talk to your local Greencross Vets about the best time to desex your dog.