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The bitch's cycle

A bitch will have her first season anywhere between the ages of 6 months and 18 months old. It very rarely appears earlier than this but can sometimes come later, all bitches are different. In my own experience with the bitches I have bred and owned, the first season usually arrives between 9 to 12 months, sometimes slightly later, and then will come regularly every 7-10 months.


Bitches have two ovaries and two uterine horns that extend down each side of their body, towards the kidneys.


A bitch’s cycle is broken down into 4 parts:


Pro-oestrus is when bleeding starts and vulvar swelling occurs – we call this Day 1 of the bitch’s season. The bleeding occurs due to heightened blood supply to the area and isn’t due to sloughing of the uterine lining as in humans. A male will be interested in a bitch at this stage, but she will not allow him to mate her. This lasts on average 9 days with bleeding often starting to become lighter in colour and opacity as it gets closer to the next phase, Oestrus. The vulva can swell to an unrecognisable size and appear floppy. She will be cleaning herself in this area constantly and this may well be the first sign that you notice.


Oestrus is the period in which a bitch will allow mating. It occurs roughly 9 days after the bleeding and swelling starts but can vary, some bitches will enter Oestrus and allow mating from as early as 1-2 days after Proestrus (bleeding) begins. Oestrus lasts on average 9 days also but again, can vary. During this time, the bitch will ‘stand’ to receive a male and any male that is near her will be wild with constant excitement. Both will flirt and play with each other, in a manner that you have never witnessed before, and the bitch will ‘flag’ her tail to the side to allow him to mount her.


It is only during Oestrus that the bitch will ovulate and can get pregnant. All the eggs that she is going to ovulate are done so at the same time and not over a period of days as once thought. Once released from the ovary, the eggs take three days to ripen and become penetrable. Once ripe, the eggs are then viable (penetrable by sperm) for 24/48 hours before dying off, this is the only time she can conceive. However, sperm can live in the bitch’s reproductive system for up to 7 days, so any mating that has occurred prior to, during or after ovulation can fertilise the eggs as the sperm will be waiting in the uterus. After her eggs have died, the bitch will, over the next few days, fall into the next stage of her cycle.


Dioestrus is the two month stage after Oestrus where the reproductive cycle is under the influence of progesterone. This is the period of pregnancy in a bitch who has successfully conceived, however, even if not pregnant or unmated, each bitch will go through Dioestrus and will have some level of pseudo (phantom) pregnancy during this time, whether detectable by you or not.


In human pregnant woman, a hormone called HCG is produced and can be detected in blood or urine which makes her hormone levels very different to that of a woman who isn’t pregnant. In bitches, hormone levels are identical, whether pregnant or not, and therefore the body behaves in the same way.


During Dioestrus you may notice that your bitch’s nipples start to enlarge, become pink and mammary development occurs, this is completely normal and, as long as you know that no male has mated her, it is purely a sign that ovulation has occurred. You may notice that her vulva still appears larger than it did pre-season but not as big as it was during. She may be more affectionate than she was previously. As the weeks pass, when her body would be pregnant if she had been mated, you may notice a change in her energy level, her mood, her appetite and her weight, this is all perfectly normal and no veterinary attention is needed. Try and increase exercise to keep her moving and cut back slightly on food to avoid maternal weight increase. She may be slightly more vocal, not as playful and behave quite differently. Don’t worry, it will all go back to normal after Dioestrus is over.


Around 10 weeks after Proestrus (bleeding) is when she would be giving birth. You may notice her mammary glands become rather large, sometimes hanging low, and she could potentially be producing milk if you were to check by squeezing a nipple. This will dry up if not stimulated. Unless a mammary gland appears red, sore to touch and hard, no veterinary care is required.


Try not to allow her to ‘nest’ with toys as she will believe they are her babies, and this will keep her milk supply longer. She can be in this state for a number of weeks, roughly the length of time she would be feeding her young, but gradually her mammary glands will decrease in size and any milk will dry up. Some bitches are left with a slight sag in their skin underneath, but for most it retracts fully over time.


These are all symptoms of pseudo (phantom) pregnancy. Whilst they can be bothersome, it isn’t a medical condition, it is a very natural response that shouldn’t cause concern. In the wild, a pseudo pregnancy served a purpose; should a bitch die during or after giving birth, the other bitch(es) in a state of pseudo pregnancy within the pack could nurse the young, and as bitches who live together often cycle simultaneously, this would not be unusual. Even though only small amounts of milk are produced in pseudo pregnancy, lactation is a ‘positive feedback mechanism’ and the more the pups nurse, the more milk would be produced, and a full milk supply could be stimulated.


Some bitches have ‘stronger’ symptoms than others in Dioestrus, but there is no way to know this prior to it occurring. There is also no way to differentiate between each stage except from Proestrus and the first sign of blood. A vet will not spay a bitch whilst she is in Pro-oestrus, Oestrus or Dioestrus, due to the heightened blood supply to her reproductive system and the possible complications this could cause during an operation. Spaying can only take place around 3 months after the bitch has come into Pro-oestrus.


Anoestrus is the longest stage of the bitch’s cycle and is a period of rest after Dioestrus, when reproductive organs are inactive. Anoestrus lasts, on average, 5.5 months. During this time there will be no sexual interest between dog and bitch. 


It is worth noting that even neutered dogs will be interested in a bitch during her season and are still able to mate her during Oestrus, even though they cannot fertilise the eggs. This is particularly important to be aware of if you own a dog and a bitch. When canines mate, a coital lock takes place and, if not supervised, can cause damage to either dog’s sexual organs, so it is best to avoid a mating at all costs. A male and female that have previously slept together overnight will need to be kept apart during this time.





This term refers to pus in the uterus and Pyometra is a serious, potentially fatal uterine disease which can occur during Dioestrus and is important for every bitch owner to be aware of. It begins due to hyperplasia (extensive swelling) in the uterine lining, from an exaggerated response to progesterone, but the reasons for this occurring are unknown. Together with the presence of bacteria, the uterus becomes severely diseased, distended and filled with pus. There are two types of Pyometra, ‘Open’ and ‘Closed’. In an ‘Open Pyometra’, the cervix is open, allowing copious amounts of strong-smelling pus to escape. In a ‘Closed Pyometra’, the cervix remains shut and all the pus is retained, making it very difficult for the owner to notice an issue initially. However, the bitch will become very poorly, very quickly, and if left untreated, the condition it is fatal. Signs include lethargy, refusal to eat, vomiting, distended abdomen, diarrhoea, enlarged or flaccid vulva, excessive drinking of water accompanied by large volumes of urine, often overnight as well as during the day. The bitch can quickly become toxic and all body systems will be involved if not dealt with quickly.


Pyometra usually occurs in bitches over 6 years old, however, it has been known to happen following a first season. It is always seen in Dioestrus, roughly mid-way through. There is no connection with pseudo pregnancy, irregular seasons or the fact the bitch hasn’t had a pregnancy. The usual treatment is to spay the bitch immediately.


Once a bitch is spayed, the risk of Pyometra has gone. (See also this blog post on Phantom Pregnancy)

Written by Di Reid

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