Oestrus, or heat, is an integral part of a female dog's life. But what exactly does it mean for you and your pooch? How do you deal with it? And what do you do if you don't want your dog to reproduce?

What is a Dog "in Heat"?

The Reproductive Cycle of a Female Dog

Oestrus, or heat, is the stage in a female dog's reproductive cycle during which she becomes fertile and receptive to mating with males. This period normally lasts about three weeks.

The female dog's heat cycle has four distinct phases:

  • Proestrus: Proestrus is the start of a dog’s heat cycle where their body is preparing to mate. During this period, the ovarian follicles enlarge and secrete a hormone called oestradiol. This initiates the development of the uterus, as well as the dilation of the vulva and vagina. Proestrus lasts an average of 9 days but can last anywhere from 3 to 17 days.

  • Oestrus: Oestrus is the mating phase of the reproductive cycle and usually lasts around 10 days, but can be as short as 3 or as long as 21 days. During this time, ovulation occurs. Oestrogen levels drop, while progesterone levels soar. There is also an increase in luteinising hormone or LH.

  • Dioestrus: Dioestrus, also called metestrus, occurs directly after the “in heat” phase and lasts for about two months. It corresponds to the luteal phase. During these two months, the corpus luteum forms in the ovary and secretes progesterone. This phase ends in either pregnancy or luteolysis.

  • Anoestrus: Anoestrus is the uterine repair phase, during which no sexual or hormonal behaviour occurs due to very low levels of progesterone and oestradiol. This phase can last for four to five months before the next proestrus phase begins.

At What Age is a Dog's First Heat Cycle?

In general, a dog’s first heat cycle occurs around the age of ten months. This can be up to twelve months for some animals. For others, heat occurs quite early, around the age of five or six months. This is normally the case for smaller dog breeds. In very large breeds of dogs, heat may occur later around the age of two.

A dog's first heat cycle can sometimes go unnoticed. This condition is known as "silent heat", in which they do ovulate but the characteristic signs of a dog in heat—vulvar swelling and discharge—are not observed. Silent heat can also occur with age. Some bitches also experience false heat, where the dog’s heat cycle stops abruptly after the proestrus phase, without ovulation occurring. These false heats are often displayed in young bitches and do not present any danger.

How Long Does a Dog's Heat Cycle Last?

The average duration of a dog's heat cycle is three weeks. This is of course only an indication. Most female dogs are in heat twice per year, or about once every six months.

The period of "rest" between a dog’s heat cycles is called interoestrus. Certain factors can affect the length of this period, such as the breed of your dog, any medical treatment, the presence of other bitches in the environment, and even the climate or season. Bitches very often come into heat at the start of spring in countries with a moderate climate.

Finally, it's important to note that dogs do not experience menopause as humans do. As such, female dogs can get pregnant throughout their life, from the age of sexual maturity until their death.

➔ Pay attention to any change of pace. Be sure to consult your vet as soon as any change arises to be sure your dog isn't sick. Likewise, a dog’s heat cycle that lasts for a long time or is ongoing may be a sign of an ovarian cyst or hypoestrogenism (oestrogen deficiency). This problem is more common in older bitches.


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How Do I Know When My Dog is in Heat?

Some signs are easy indications of a dog in heat. First of all, your dog's vulva will swell. You may also notice a blood-tinged discharge. These symptoms correspond to the proestrus phase. Your female dog secretes sex pheromones to attract males, but she is not yet receptive to mating with them and may become aggressive if they try to mount her.

During the oestrus phase that follows, the vulva continues to swell, but blood flow will lessen and then stop. The discharge may continue in a lighter, clearer colour. During this period, female dogs in heat will attract and accept males. Please note: It is not possible to stop a dog’s heat cycle naturally.

You will also notice a behaviour change when your dog is in heat. These changes are quite variable: some dogs in heat are much more cuddly and clingy than usual, while others are more aggressive.

What Do I Do When My Dog is in Heat?

If you don't want your female dog to reproduce, then the first thing you need to do while your dog is in heat is to avoid all contact with non-castrated males. To do this, during your dog’s heat cycle, always walk her on a lead! Even if she's well trained to come back when you call, when your dog is in heat, she may well turn a deaf ear.

If you have a garden, make sure it's securely fenced! Not only to prevent your dog from scampering off but also to prevent any surrounding males from entering while your female dog is in heat. Be aware that you risk a fine of up to £1,000 if your dog is found straying in public. In addition to this, the risk of them breeding is high, and you could end up with an unwanted litter.

In a more practical sense, you can also buy dog nappies and pads to prevent blood loss or discharge from soiling your interior.

How Do I Stop My Bitch from Coming into Season (Heat)?

Spaying (Neutering)

Spaying is the safest and most effective way to keep your dog from coming into season. This method is permanent. It not only allows you to prevent your female dog from having her heat cycle, but it also protects her from certain diseases, such as tumours forming in the teats, ovaries, and uterus. Spaying is perfectly safe for your bitch, except for the potential risks of anaesthesia, which are the same for all surgical operations. Spaying also helps prevent phantom pregnancies.

If you are not planning on breeding, have your dog spayed before her first heat cycle. Contrary to popular belief, female dogs do not need to have at least one litter in their life to be healthy. However, spaying also has some drawbacks that it's good to be aware of. A neutered bitch can gain weight more easily. It's also possible, but rare, that she will become incontinent. Fortunately, it's possible to correct this problem later on.

Hormone Injections

You can also prevent a bitch from coming into heat with the use of hormones, in the form of injections. This solution is only temporary and generally aims to prepare for mating with a breeding male. It is not recommended to repeat the injections too often.

There are also pills which can stop a dog’s heat cycle, but they have dangerous side effects. Be careful when using such products. If you're sure that you don't want your dog to have pups, then have her permanently neutered. This will save you a lot of hassle.


By the Hector Kitchen medical and scientific team


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