Helpful Guidance for Supporting Dogs in Season

What is a season?

‘Season’ is a term used to describe the time when a female dog is receptive to males and fertile if mated. People also use the terms ‘in-heat’ or ‘on-heat’. Technically the ‘season’ only refers to oestrus, when a female dog allows mating and is fertile, however most people use the term to cover pro-oestrus as well from when she starts to show external changes.

The hormonal cycle of female dogs

Most female dogs have a hormonal cycle lasting around 7 months, though it can be as short as 4 months, or over a year. When a female dog reaches puberty she will have her first season. The hormonal cycle has four stages.

• Pro-oestrus: Oestrogen and progesterone levels rise, the vulva swells, and there is a blood tinge discharge from the vulva. Males may be attracted to the female during this stage, but she usually won’t allow mating. This stage is usually 7-10 days long.

• Oestrus: Oestrogen falls, and progesterone continues to rise, the vulva becomes less swollen, and the discharge becomes less blood-tinged. Oestrus starts several days before ovulation and eggs must mature before they are fertile. Most matings during this period, which lasts around 7 days, will potentially produce puppies.

• Metoestrus/Dioestrus: The ovary continues to produce progesterone for around 55 days in both pregnant and non-pregnant female dogs. In non-pregnant dogs, birth follows the sharp drop in progesterone and a rise in prolactin. Prolactin causes mammary development and milk production as well as maternal behaviour. Non-pregnant females can suffer physical and behavioural signs known as false or phantom pregnancy due to these hormonal changes.

• Anoestrus: This is the period after the season which lasts for around 4 months in most female dogs. Oestrogen and progesterone are at very low levels and the mammary tissue and vulva reduce in size. At the end of anoestrus follicle stimulating hormone and luteinising hormone rise and start the next cycle.

When will my dog have her first season?

Female dogs can have their first season from around 6 months to 18 months of age. Smaller breeds tend to reach puberty faster than large breeds. The first seasons can be short, split, or happen with mild external signs.

How will I know when my dog is in season?

You may notice some behavioural changes in your female dog before her season. She may start to urine mark on walks, become more or less friendly with other dogs, and her attitude to training may change. Before the first season, the vulva and nipples will start to enlarge.

At the start of pro-oestrus, she will pass small amounts of blood-tinged discharge from her vulva. This can be tricky to spot, and breeders may put a white sheet in their dog’s bed or test the vulva with white tissue paper. Some girls are very clean so increased licking may be the first thing you notice. After the discharge starts the vulva swells to a very large size. Male dogs will be interested in your dog and her urine. Female dogs may engage in humping together.

How long will my dog be in season?

The length of pro-oestrus and oestrus is variable, but most female dogs show external signs and are attractive to males for 3-4 weeks. After about 10 days bloody discharge reduces and the vulva starts to decrease in size. This does not mark the end of the season but the start of the fertile period! The season ends 5 days after ovulation when the eggs are no longer fertile, but there are no external signs other than refusal to accept a male to indicate this has occurred.

How often will my dog have a season?

The average time between seasons is 7 months but it can be as short as 5 months or over a year. Very short cycles can be linked to hormone and fertility problems. The Basenji breed only has one season a year.

Female dogs do not go through menopause and can continue to cycle and be fertile into old age. The Kennel Club will not register puppies from mothers who are 8 years old or older when they give birth. Most breeders would prefer a mum to be between 2 and 5 years old for her first litter, but this can vary with breed.

How do I look after my dog during her season?

Once you notice your dog is in season you may need to adjust her lifestyle to keep her safe, as well as to be fair to other dog owners. Think carefully about where you will exercise your dog. Avoid places where male dogs may be off lead as they may harass or try to mount your dog.

Check whether any training classes or dog events you were planning to attend allow in-season dogs to participate. Some female dogs appear to have cramping in pro-oestrus and may be less willing to engage in training or walks, and others may be more anxious than usual. Every dog is different so try to observe your dog and understand what she needs.

When is my dog most fertile during her season?

Ovulation occurs 12 days after the start of pro-oestrus on average, but it can happen as early as day 5 or as late as day 25. Eggs are not fertile until 2 days after ovulation and remain fertile for 2 more days. Most females allow mating just before ovulation and sperm can be viable for as long as a week which means there is a window of about 9 days in which a mating can result in puppies.

If you want your dog to have puppies it is important to know when she ovulates to maximise the chance of a successful mating and to predict when puppies are due. This can be done through testing her blood progesterone levels. Other methods such as vaginal cytology, ferning, ovulation pads, and behaviour are less accurate.

If you do not want your dog to have puppies she must be kept away from male dogs for the whole of her season. If she is accidentally mated your vet can advise on injections which will prevent pregnancy. If your dog is accidentally mated never try to separate the pair as this can result in injury to both dogs.

How can I prevent my dog from having puppies?

There are two main options for preventing unwanted litters: keeping your dog away from males during her season and neutering her. Neutering (often called spaying) involves the surgical removal of the ovaries with or without the uterus. Neutering has many health benefits for dogs not required for breeding but also has some negative effects.

Neutering should be discussed with your vet who can give the best advice for your dog and situation. Neutering should be carried out 3-4 months after a season and when false pregnancy symptoms have subsided. Neutering can be carried out at 4-6 months, before puberty, but this approach is not common in the UK and may be linked to health and behaviour problems, especially in larger breeds.

Less common ways of preventing pregnancy include removing the uterus but leaving the ovaries, tying the oviduct, or using a hormone implant.

Health problems for female dogs after a season

Dogs are unusual in that their hormone levels are similar post season in pregnancy and non-pregnancy. This means there is no early pregnancy test for dogs, with available tests only working halfway through gestation. This also means most dogs will show some degree of false or phantom pregnancy.

False or phantom pregnancy is caused by the drop in progesterone about 8 weeks after ovulation in the non-pregnant dog (a little earlier than in pregnant dogs). This causes a rise in prolactin which leads to mammary development and maternal behaviour. Most cases are mild and will resolve with decreased food and increased exercise. If your dog has a large amount of milk, abdominal pain, or severe behavioural signs consult your vet for medication to relieve her symptoms.

Pyometra is a life-threatening womb infection that is most commonly seen in older female dogs. Up to 24% of entire female dogs over 10 years old may get pyometra. Symptoms include lethargy, vomiting, drinking and urinating more, and in some cases a foul-smelling vaginal discharge.

Pyometra is treated by surgical removal of the pus-filled uterus, but the operation is riskier than a standard spay as the infection can affect the heart and kidneys. Complications can include uterine rupture, bleeding, death during surgery, and kidney failure. In very sick dogs medication can be used to make the uterus expel the pus allowing surgery once the dog is fitter and stronger, but the medications are not licenced for this purpose.

Key facts on seasons in dogs:

• The first season can happen from 6 months old.

• Seasons happen every 7 months on average.

• Seasons last for about a month and the dog is fertile for around 9 days when discharge and swelling reduce.

• Neutering 3-4 months after a season prevents pregnancy but has a mix of health benefits and risks which you should discuss with your vet.

Do you need further advice?

If you need any further advice, please contact the OSCAR Helpline Team on our freephone number 0800 195 8000 or email helpline@oscars.co.uk.