Female dogs (bitches) naturally reach puberty age any time between around 5-12 months of age, depending on size and breed (smaller dogs tend to come into season earlier and bigger breeds later). Physically, smaller breeds will mature earlier than large breeds too (who may take up to 24 months until they are physically mature).
Puberty is a stage that happens within the period of adolescence and is associated with a lot of brain changes. When a bitch reaches puberty, they will have their first season. It is only while a bitch is ‘in-season’ that they can get pregnant.
The first stage of a bitches season is called ‘pro-oestrus’. This is when their vulva becomes swollen and they bleed for around 9 days (although it can last for anything between 3-21 days!) and then bleeding reduces and they become fertile for around 5 days (discharge often changes to straw coloured).
It is commonly thought that a bitch is fertile during the bleeding stage, but it is important to note that the days following the bleeding are actually when the bitch is ovulating.
Whilst they are in-season, particularly during the fertile stage, they will be very attractive to male dogs who will scent her from many miles away, and the urge to find a bitch ‘in-heat’ can cause male dogs to break out of gardens, roam and travel long distances following the scent.
Equally, bitches will be motivated to find a mate, and this can cause them to also roam and be more inclined to meet other dogs.
They will also urinate more as they leave pheromone messages for other dogs to pick up that she is in heat.
If an unneutered male finds a bitch in-oestrus, they will ‘tie’ which means that you would be unable to split them up once the dog mounts the bitch, in fact, it can be dangerous to try to split them.
You will need to wait and then take the bitch to the vets to have an injection that terminates the potential pregnancy.
Sometimes, first seasons can be quite subtle, or particularly long, or sometimes even split a few weeks apart. You may notice some spots of blood on the floor or your bitch licking herself a lot keeping herself clean.
She may seem more lethargic and if she lives with other dogs (or other dogs come near her on walks) you may notice her appear to behave a bit flirty.
When she is fertile, she will ‘stand and present’ and hold her tail to one side towards them. It is advisable to keep your bitch at home whilst she is in season. Or at least keep her on a lead, walk her in areas away from other dogs and at less sociable hours whilst she is bleeding.
Then keep her at home for several days once the bleeding stops until her vulva returns to normal size and all other signs of her oestrus cycle stops.
You will need to substitute physical exercise with additional mental stimulation for these 3-4 weeks.
If you have an unneutered male at home, it is vital that you keep them completely separated although this will still be very stressful for your male dog. It may be advisable to ask friends or family to look after him or put him into kennels until your bitch’s season is fully complete.
The stage after a bitch’s season is called ‘metoestrus’ which lasts between 45-90 days. If a bitch is spayed during this period, there is potential for lifelong complications. Hormones during this stage are telling the dog that she is pregnant and caring for puppies, whether or not she is actually pregnant.
This can lead to some physical or behavioural signs such as enlarged mammary glands, production of milk, nesting and mothering items, for example.
When signs are apparent, this is known as a Phantom Pregnancy – if there are physical signs or more severe behavioural signs such as aggression it is important that you speak to your vet as your bitch will need medical treatment.
Even if there are no symptoms, it is sensible to wait until 19 weeks after the first signs of bleeding before spaying to ensure that hormonal levels are as low as possible to prevent a bitch from getting stuck in the phase which is telling her body she has puppies!
A bitch will normally have repeat seasons every 6-12 months unless they are spayed. There is a higher risk of mammary tumours the more seasons a bitch has, and a risk of ‘pyometra’ (womb infections – which is a medical emergency) in unspayed bitches.
However, it is also important for brain development for bitches to be allowed to mature physically, sexually and socially prior to neutering.
As with most things, the decision about when to spay in terms of number of seasons is very individual as it will depend on breed, size and personal circumstances and should be discussed with your vet.
However, if you do not plan to breed from your bitch (which involves a huge amount of research and time to do so responsibly), it's always recommended to spay.