How Long Will Your Female Dog Be In Heat?

If you have a non-spayed female dog, the prospect of her going into season can be pretty daunting. We’ve all heard stories of accidental litters, stained carpets and plenty of conflicting advice on everything from how to exercise a dog in heat to when you should get your dog spayed. First things first though, how long is a dog’s season meant to last? To get to the bottom of everything, we spoke to Dr Aimee Warner, veterinary surgeon, for expert guidance on what exactly it means when your female dog is in season, the signs to look out for and how a dog’s reproductive cycle works. Here’s everything you need to know. 

Main takeaways

• The phrases ‘in season’ and ‘in heat’ tend to refer to the fertile stage of a female dog‘s reproductive cycle. This stage lasts between 2-4 weeks.

• Most dogs will come into season every 6-7 months. Smaller breeds will experience their first season at around six months. Larger breeds could take up to a year.

• The best way to prevent unwanted pregnancies, infection and other illnesses is to get your dog spayed.

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How long is a dog in season?

Lots of people use the terms ‘in heat’ and ‘in season’ interchangeably. Technically though, the term ‘in heat’ is the one that refers to a specific stage of a dog’s season called the oestrus cycle – the fertile part. When a female dog reaches sexual maturity she’ll begin to experience a cycle roughly twice a year. 

Dogs typically remain in heat for anywhere from two weeks to as long as four weeks.

As female dogs do not have a menstruation cycle like humans where we shed the lining of the uterus, they do not experience menopause. This means dogs will continue to have seasons throughout their life with reducing fertility (although complete halting of reproduction has been documented).

Theoretically, this means a female dog could have puppies later in life – something that should be avoided as there is risk of an unhealthy pregnancy at an older age. The main risk of repeated cycles for dogs however, is getting pyometra – an infected uterus – as each cycle opens the cervix, allowing bacteria to enter. Pyometritis is a life-threatening condition that may require expensive and invasive surgery. The best way to prevent it is to spay your dog while they are young and healthy.

When do dogs go into season?

When someone says a female dog is ‘in season’ or ‘in heat’ it means she’s fertile, or just about to be. “Most dogs will come into season every 6–7 months,” Dr Warner tells us, “but some, especially larger breeds, may have them less frequently.” It is typical for female dogs to experience roughly three seasons in two years.

Most UK pet parents choose to spay their female dogs – an operation called an ovariohysterectomy removes the ovaries and the uterus meaning their dog will no longer have seasons or be able to get pregnant. Some practices do now offer a new keyhole surgery called an ovariectomy just to remove the ovaries. For male dogs, this operation is called castration and involves removing the dog’s testicles so he can no longer produce sperm. Dogs who have been spayed do not experience a fertility cycle.

“Exactly when a bitch will come into season varies depending on breed and size,” explains Dr Warner. “Most smaller dogs will have their first season at around six months old, whilst larger breeds may not come into season until they are more than a year old.”

The first couple of seasons can be a little all over the place and sometimes the first season is split. This means the pup can appear to be in season for 5–7 days, then again a few weeks later for the expected amount of time.

Phases of a dog’s season cycle

As a whole, a dog’s fertility cycle is known as the oestrous cycle, and it’s made up of four stages:

• Proestrus

• Oestrus

• Dioestrus

• Anoestrus

Proestrus 

Lasting from 3–17 days, this stage is when your dog‘s body is preparing for the possibility of pregnancy. Her oestrogen levels will increase which causes an oedema (swelling) of the vulva (which can become much larger than normal) and the uterus as blood vessels dilate.

Some of this blood might seep through, which is the source of any blood spotting you may notice. This is very different to the lining of the uterus shedding during the human reproductive cycle (no pain or period cramps involved!). This is the stage where you’ll begin to notice increased attention from male dogs and some behavioural changes. Male dogs can often smell when a bitch is in the proestrus or oestrus stage from a surprising distance – especially if they haven’t been castrated. 

Oestrus

Confusingly similar in name to the cycle as a whole, the oestrus stage is 3–21 days long and it’s in this stage that your dog will ovulate. Multiple eggs are released – and your dog may be able to conceive multiple puppies. The discharge from her vulva will turn paler and more watery as her levels of the pregnancy-supporting hormone progesterone rise and her oestrogen falls. She’ll also be releasing the pheromones and hormones that signal her fertility to male dogs (she may be urinating more frequently in small bursts to help spread that message by marking). You’ll need to keep a close eye on her during walks to avoid unwanted attention and unplanned pregnancy. Mating can result in conception up to five days either side of ovulation as canine sperm is viable for approximately seven days.

Dioestrus

Lasting 2–3 months, this is the cooldown time after your dog’s fertile period (which lasts up to five days after ovulation during the oestrus stage). During dioestrus, her progesterone levels rise and peak before steadily falling until the next stage. You’ll notice her vulva return to its normal size, and she’ll no longer be interested in mating with male dogs. They should be less interested in her, too. However, it’s not always obvious when your dog has entered this stage of her cycle, so it’s best to continue to keep a close eye on her until four weeks have passed since her discharge began. 

Anoestrus

The dormant stage in a dog’s reproductive cycle, this lasts on average 4–5 months. Your dog’s hormones will have returned to normal levels during this time and she cannot get pregnant. Inside, your dog’s uterus is slowly preparing for her next heat cycle. This is the recommended time to get her spayed – ideally three months after her season. 

How can you tell your dog is in season?

It’s important to recognise the signs that your dog is entering her heat cycle and will be fertile soon. Caused by hormonal changes which prepare a dog’s body for mating and pregnancy, your dog may experience some discomfort, but she shouldn’t be in pain. The signs include:

Physical changes

• Swollen or enlarged vulva. This often happens a few days before bleeding starts.

• Vaginal discharge which is initially bloody then becomes watery. When less bloody it can be harder to notice. Discharge usually lasts 7–10 days in total.

• Cleaning and licking their vulva more often.

• More frequent urination. 

Behaviour changes

Your dog’s hormones can also have a powerful effect on how she acts (and whether she listens to you). “Their behaviour can also change before and throughout their season. For example, they may be less willing to listen to commands or seem distracted,” says Dr Warner. “Other signs can include a reduced appetite or territory marking.” They may seem agitated or start whining more for no apparent reason. This can cause pup parents some worry, but it is natural.

“They ovulate and are fertile usually after the bloody discharge stops, this is when they are receptive to male dogs,” says Dr Warner. “Typically, this will be around 10–14 days after the discharge started.” 

Testing

Unlike with humans, testing scientifically that your dog is in season isn’t as simple as peeing on a stick in your bathroom at home. If you really want to know if your dog is in heat, some vets offer a canine vaginal cytology test which involves testing cells from their vaginal wall or a blood test that will look at their levels of hormones.

What to do when your dog is in heat?

When she’s in season, there’s a lot going on inside your dog’s body. She may seem anxious, uncomfortable and even confused, so it’s important to show her extra TLC while she’s in season.

Keep a close eye on her during walks

On top of the risk of pregnancy from uncastrated male dogs, attention from other dogs can be stressful, so it’s a good idea to avoid busy parks while your dog is in season. Male dogs may be pushy about getting close to her, wanting to sniff her vulva or try to mount her if they get a chance. When mating, dogs get ‘locked’ together, tail to tail, facing away from each other. If your dog gets mounted by another dog this position can be a shock to humans as it is not widely recognised. Both dogs can also become quite stressed by it, so if it does happen, keep both dogs calm until they release each other naturally.

To avoid the likelihood of unwanted mating, opt for quieter routes or times of day, with her lead on so she can get some exercise without having to deal with potential suitors. If a male dog does appear to be making an advance, let the owner know that your dog is in season as soon as possible. Calmly separate them and lead your dog a safe distance. 

Play with her more at home

As she’ll need to be on her lead or walked at quieter times, as walkies are likely to be less stimulating during her season. Up the fun while you’re at home with games like tug and enrichment activities like a snuffle mat, which will keep your dog mentally stimulated.

Be mindful of mess

While your dog is in season, bloody discharge is normal for up to 10 days. How heavily a dog in heat bleeds varies, with larger dogs tending to bleed more heavily. Discharge from your dog’s vulva can stain carpets, furniture and fabrics so some pet parents limit access to sofas and carpeted rooms, lay down old towels or puppy pads in their dog’s favourite spots.

Specially designed nappies, washable pants and sanitary pads are available, though it can take some trial and error to find the right fit for both your dog’s comfort and your sofa cushions. If you’re concerned about the amount your dog is bleeding, if any clots are seen, or if the blood has a foul smell, consult your vet. 

Avoiding pregnancy

It is almost impossible to differentiate exactly between the different stages of a dog’s cycle. Even vets can only just about tell from vaginal swabs and cells looked at under a microscope, so it’s best to err on the side of safety. Keep her supervised while out and about and away from non-neutered male dogs for four weeks to be sure to avoid her getting pregnant.

Frequently asked questions

How will I know when my dog’s season has finished?

When your dog’s season ‘ends’ or enters the dioestrus stage you may notice a reduction in vulva size, an absence of discharge and a lessening of the restlessness or friendliness with other dogs that she may have been showing. 

However, it is almost impossible to differentiate exactly between the different stages of a dog’s cycle. Even vets can struggle with vaginal swabs and cells looked at under a microscope, so it’s best to err on the side of safety and continue the precautions you put into place when your dog is in heat.

How long is a dog bleeding in heat?

Dogs in heat will usually bleed for around 7–10 days, starting in the dioestrus stage. If your dog stops bleeding, this does not mean she is not fertile. In fact, it’s important to remember that when her discharge turns paler, more watery and becomes less noticeable, she is actually entering the oestrus stage where she ovulates and becomes fertile.

Some dogs can have a ‘silent heat’ where no signs show but they are still cycling and can become pregnant. Most owners will think they skipped a season.

What are the four stages of a dog’s season?

Your dog’s season is made up of four stages: ‘proestrus’, when your dog’s body is preparing for a possible pregnancy, ‘oestrus’, when your dog will ovulate, ‘dioestrus’ (the cooling down period) and the ‘anoestrus’ stage when your dog’s reproductive cycle is dormant.

References

“ Understanding Normal Canine Behaviours.” The Royal (Dick) School of Veterinary Sciences, The Jeanne Marchig International Centre for Animal Welfare, 2019, 

“ Dog and Puppy Neutering.” Royal Veterinary College, Accessed 18 Dec. 2024. 

Romagnoli, Stefano. “ Canine Breeding Management – Optimising Fertility.” Vet Times, 2014