Knowing whether your female dog is coming into heat (“in season”) is usually fairly obvious. A number of symptoms are associated with this specific reproductive phase, some, if not all, of which, should be visible.

Such indicators would usually include excessive licking of the genital area and a bloody discharge from her vulva. The vulva will also have become much more swollen than usual. Her tail may be held low and tucked between her hindlimbs, particularly when approached by another dog. She may also show altered or unusual behaviour such as aggression, nervousness or agitation. Entire (un-neutered) male dogs will start to show an increased interest in her, as those pheromones (doggy chemicals) start to flow! Her appetite may also be altered.

When will it occur?

The timing of a female dog’s first season is variable and will be largely dependent on her breed and thus size and bodyweight. Genetics and environmental factors (such as good quality nutrition versus malnutrition), may also influence the exact onset of events. Most dogs will start their seasons somewhere between 6-15 months of age. As a broad rule of thumb, the larger the breed of dog, the later the season will commence, and some large and giant breed dogs may be even older than the 15 month mark when they first come into heat. A season is the only time during her sexual cycle that your dog is able to become pregnant.

So, what exactly happens?

The season itself will usually last somewhere between 2 and 3 weeks. During this time both the nature of her vaginal discharge and her receptiveness to male dogs will change. 


The initial bloody discharge may last somewhere between 7-10 days: this is the “pro-oestrus” phase of her cycle. At this time, she is neither responsive or receptive to the advances of any male dog and may show aggression towards any any that approach her. She may also become clingier to you, her owner.

In heat

In the following 7-10 days however, the bloody discharge lessens and is replaced with more of a clear or straw-coloured fluid. The bitch may increase her frequency of urination as a means of scent marking. This signals her readiness to breed with a male dog. She is now in full “oestrus” and is receptive to mating. Professional breeders would typically allow mating to occur on days 11 and 13 of the female dog’s cycle, as this is thought to correspond with peak fertility. They may also use hormonal blood tests or combine this with vaginal cytology (looking at cells down a microscope), to best determine the optimal time of mating. 

During the height of her season, the sensible advice is to keep your dog on the lead when out exercising. Pay close attention to and observe her at all times to ensure that an accidental mating does not occur. In the house, many owners use commercially available doggy pants or nappies to absorb the discharges and keep everything clean.

And after that?

“Dioestrus” then follows and lasts anywhere between 60-90days. This correlates with a return back to normal or, alternatively, pregnancy. This phase is also where many reproductive health problems may occur, such as a false pregnancy (pseudopregnancy) or uterine infection (pyometra).

“Anoestrus” is the sexually inactive time of the bitch’s cycle and corresponds to both normal hormonal and normal sexual behaviour. It forms the majority of time between consecutive seasons. Many dogs will cycle twice a year at 6 month intervals. However, just like humans, certain individuals may have seasons with lesser / greater intervals apart than this. Furthermore, a small breed dog may cycle every 4 months and a giant breed dog perhaps only once every 12 months.

My dog is one year old and I’ve not seen a season yet…

Occasionally, her first season is very subtle and small, with no distinctive outward or visible signs. If your dog is particularly clean, she may spend quite some time licking and it may therefore be hard to appreciate any vaginal discharge. She may also be experiencing a “silent oestrus” and just will not show any obvious overt symptoms. In such cases, it would then follow that her first apparent season is seen once she has reached one year of age.

Other possible abnormalities with a season

Occasionally a prolonged heat may be seen, which lasts longer than the average 21 days. Caused by persistently elevated oestrogen hormone levels, in a young dog, this may be because of an active ovarian cyst. One occurred; this specific problem is likely to also manifest with subsequent heats.

A split heat is another abnormal pattern to the season in which the completion of normal heat is delayed. The dog will start the season as expected yet emerge out of it without ever having shown the receptiveness to male dogs. The second half of the heat then occurs weeks to months later.

An absent heat is also another abnormality, albeit these are generally very rare.

So, if I wish to do so, when is the best time to spay (neuter) my female dog?

The answer to this question will vary enormously! There are many factors to take into consideration and the breed and thus ultimate bodyweight of your pet probably has the largest influence. Pro’s and con’s of neutering at any specific time exist. It is best to get personal and tailored advice from your Veterinary Surgeon as to what is considered optimal for your specific pet.