Dogs and cats are placental mammals that carry their foetuses in the uterus to full term, giving birth to a litter of live offspring that are almost fully developed. Offspring are initially fed on milk secreted by the bitch or queen’s mammary glands, with puppies and kittens suckling on the five or four pairs of teats, respectively.
The reproduction process requires a number of different organs, hormones and events that all work together in a system, to produce puppies and kittens. In this article, we’ll explore the components and functions of the female reproductive system, the disorders that can affect reproduction, and what to look out for when problems affect the reproductive organs.
Components of the female reproductive system
The canine and feline female reproductive system consists of many different parts that each play an important role in the process of reproduction. The main female reproductive tract of both dogs and cats is located in the abdomen, starting below the kidneys and extending into the pelvis. Both dogs’ and cats’ reproductive tracts are similar in shape, but there are size variances between species as well as between different sized dog breeds.
Their reproductive system is defined as multiparous, meaning it can carry many foetuses in the course of one pregnancy. This is due to the uterus being bicornuate – its Y-shape consisting of two long uterine horns along which the multiple fertilised eggs are deposited.
The components of the reproductive tract include:
Ovaries
Like human ovaries, there are two canine and feline ovaries on either side of the abdomen, held in place by the ovarian ligament. The ovaries produce ova (or eggs) as well as the reproductive hormones: oestrogen and progesterone. The ova are ‘caught’ by the infundibulum – a funnel-like structure that combs over the ovary during ovulation, and moves the ova into the uterine tubes.
Uterine tubes (oviducts)
The ova travel down the uterine tubes or oviducts (equivalent to the fallopian tubes in humans) towards the uterine horns. When dogs mate, the male’s sperm travel up the uterine horns, all the way into the uterine tubes, since it is here that the ova are fertilised. Fertilised eggs are then moved into the uterine horns to be deposited at equal intervals where the foetuses will begin to grow and develop.
Uterus
The Y-shaped structure of the canine and feline uterus consists of the uterine horns and a relatively small uterine body where they are joined. When the fertilised ova are implanted in the horns, the uterine wall’s endometrial layer expands to receive the eggs and to start developing the placentae. The myometrium comprises smooth muscle, which is responsible for the contractions during birth that are necessary to push the foetuses out. The mesometrium is the outer layer of the uterus and forms part of ligaments that hold internal organs in place – the visceral peritoneum.
Cervix
The body of the uterus ends at the cervix, which is a firm sphincter-like organ – the function of which changes depending on the dog or cat’s reproductive state. Normally there is a narrow cervical canal that runs through the cervix, which is closed to protect the uterus from infection. During mating, the cervix relaxes and allows the male’s sperm to pass through into the uterus. When the bitch or queen is pregnant, the cervix is closed off with a mucoid plug to protect the gestating foetuses. When she is ready to give birth, the cervix dilates, which will allow the puppies or kittens to be expelled. The cervix connects the uterus to the vagina.
Vagina
In both dogs and cats, the vagina is a long, flexible tube that runs from the cervix to the urethral orifice (from which the bitch or queen urinates). The vagina has a large capacity to extend and dilate, thanks to the folds in the vaginal mucosa, making it easier for puppies and kittens to pass through during birth.
Vulva
The vulva is the external female sex organ, which is visible under the dog or cat’s tail, below the anus. In dogs, the vulva enlarges during oestrus, signalling – along with pheromones – to males that she is receptive to mating. In cats, there is almost no visible change in the vulva when they are ready to mate.
Mammary glands
While not part of the reproductive tract, the mammary glands do form part of the reproductive system in that their function – lactation – is influenced by the hormones that govern the reproduction processes.
- progesterone is produced in the ovaries and enlarges the mammary glands during oestrus and pregnancy, preparing for lactation
- prolactin is produced in the pituitary gland and signals to the mammary glands to start the process of lactation during the last stages of gestation
- oxytocin is secreted during birth and when the puppies/kittens start to suckle. Not only does oxytocin influence the letdown (release) of milk, but it activates the attachment between mother and neonate, regulating maternal care to ensure the offspring’s survival
The functions of the female reproductive system
The female canine and feline reproductive system has a number of functions all related to the different stages of reproduction:
- the release of ova from the ovaries in order to be fertilised
- the production of female hormones
- the receiving of male spermatozoa and providing a site for fertilisation
- the implantation of fertilised eggs and the growth of viable foetuses
- the provision of a safe passage for foetuses during the birthing process
- the production of milk for offspring during nursing
How does the female reproductive system work?
The reproductive system is governed by hormones, which work together to create the reproductive cycle in bitches and queens, and activate the different organs and functions of the reproductive system. The dog’s reproductive cycle makes her available for breeding (‘on heat’) once or twice a year, so dogs are considered to be monoestrous, while cats are polyoestrous, meaning they are on heat multiple times per season (typically every two or three weeks) unless they become pregnant or are spayed.
Dogs typically reach sexual maturity when they are between eight and 18 months old (depending on the breed and size; larger dogs reach puberty later). Cats become sexually mature earlier than dogs do – they can start breeding at as early as four months old (which is why they typically need to be spayed earlier than dogs if you don’t want your cat to get pregnant).
In cats and dogs, sexual maturity means the start of the oestrus cycle, which has four phases:
- proestrus – The ovaries produce oestrogen and release ova, which are in the early stages of being ready for fertilisation. Female dogs and cats’ behaviour may be more affectionate and playful, there may be a bloody discharge from the vagina, and the dog’s vulva may become noticeably swollen. They may exhibit restlessness and frequent urination. Despite these changes in behaviour, the females are not yet ready to mate.
In dogs, proestrus lasts between five and 20 days. In cats, proestrus can be one to four days long.
- oestrus – There is a reduction in oestrogen, but an increase in progesterone and the female is now ready to mate. Her behaviour will change: both dogs and cats will display patterns of marking behaviour, which releases pheromones to tell males in the area that they are available for mating. Cats may cry loudly and try to escape the house. If there are intact tom cats in the area, they will try to enter the house to mate. Cats are known as ‘induced ovulators’ – they will only release eggs in response to a mating. On average, they need around four matings for successful ovulation.
In dogs, oestrus can last from four to 24 days (with an average of nine days). In cats, oestrus can last from 10 to 14 days (with variation between queens).
- dioestrus – Progesterone reaches its peak while oestrogen levels have dropped significantly. If the dog or cat has mated successfully, the first signs of pregnancy will start to show: swelling mammary glands, lethargy, loss of appetite, weight gain, but also being more affectionate.
Some bitches and queens experience a false pregnancy (pseudopregnancy) during dioestrus – showing all the signs of pregnancy, but not being pregnant. This can be very distressing to your female pet, as biologically, she believes she is pregnant. If you are concerned about your unspayed female dog or cat being pregnant, take her to the vet to make 100% sure. If you don’t want her to get pregnant, it is much healthier for her in the long run to be spayed as soon as possible after five months for cats, and six months for medium-sized dogs.
In dogs, dioestrus can last up to two months if the dog is pregnant, and up to 100 days if she is not pregnant. In cats, dioestrus can last around 42 days if she has a pseudopregnancy (not pregnant), and up to just over two months if she is pregnant.
- anoestrus – Both oestrogen and progesterone are low and female cats and dogs are not interested in mating or breeding. Anoestrus occurs after a heat cycle or after the bitch or queen has delivered her litter.
In dogs, this stage lasts for the remainder of the season (approximately five months). In cats, anoestrus lasts around 10 days before her next proestrus cycle begins. She will be in heat every two to three weeks, which is not healthy for her in the long term and can cause ovarian cysts and cancers. It is healthier for cats and dogs’ lifelong health and wellbeing to be spayed.
Problems in the canine and feline female reproductive system
As with any complex biological system, the reproductive system is subject to disorders, disease and other problems. The following are brief descriptions of the most common issues the vet may encounter with female pets’ reproductive systems.
Pyometra
When unspayed dogs (and less commonly, cats) continue to have heat cycles without getting pregnant, hormonal changes can cause the thickened uterus lining to develop cysts. These cysts along with other retained fluids in the uterus create the ideal conditions for bacterial overgrowth and infection. The symptoms of pyometra include loss of appetite, vomiting, lethargy and more frequent urination. There may be a discharge of blood and pus, however, if the cervix is closed, the pus and blood in the uterus accumulates, causing the abdomen to swell. This can very quickly cause the animal to go into shock and die.
The quickest way to treat pyometra is a radical hysterectomy – removing the ovaries and uterus – or spaying. Pyometra can be entirely prevented by spaying your female dog or cat before their first heat.
Metritis
Metritis is the inflammation of the uterus, which occurs after the cat or dog gives birth. It’s caused by a bacterial infection. If the animal has had a long and difficult birth and has not expelled all the foetuses and/or placentae, it can cause the infection and resulting inflammation. Aside from a pus-like vaginal discharge, the bitch or queen may be feverish, generally unwell, may lose her appetite and be depressed, which can cause them to not tend to their litter. The puppies and kittens will be vocal and restless, which will warrant your attention and it’s recommended to take your dog or cat to the vet.
After performing diagnostics, the vet can administer treatment to help the bitch or queen expel any placentae or foetuses, and then discuss the right time to have her spayed after recovery.
Mastitis
Inflammation of the mammary glands in dogs usually occurs after giving birth and is caused by a bacterial or fungal infection. It is rare in cats. Sometimes there is no infectious cause and it can be triggered by a build-up of milk and/or the post-partum death of a puppy/puppies. The bacteria can enter the mammary tissue because of trauma to the teat, combined with unsanitary nursing conditions, or the mother trying to ween her puppies too early. Mastitis can affect the quality of the milk, so it must be treated at the vet as soon as possible.
There are various types and degrees of mastitis, so treatment will depend on the type and how sick the mother is. It can range from hospitalisation and surgery, to antibiotics, hand-milking, warm compresses, cold laser therapy and even cabbage compresses to reduce inflammation.
Follicular cysts
These are also called ovarian cysts – little sac-like cysts that develop on the ovary and disrupt the natural hormone cycling of the dog or cat. It can cause the animal to be on heat continuously and it can also lead to the development of pyometra. Follicular cysts usually develop in older dogs and cats (aged five years and older) and are diagnosed with an ultrasound and blood tests. The condition can be treated by spaying the bitch or queen, but if not, they will need close monitoring to prevent other diseases and disorders of the ovaries and uterus.
Dystocia
Dystocia is the cover-all for a diagnosis of difficult or abnormal birthing. It can be caused by:
- uterine inertia – the uterine muscle is unable to contract strongly enough to expel the foetuses during birth
- obstruction in the birthing canal – a common feature of narrow-hipped dog breeds birthing large-headed babies (as seen in boxers, Boston terriers, Scottish terriers, English and French bulldogs) or those who have fractured their pelvis
- foetal anatomical changes – oversized foetuses, dead foetuses, two foetuses presenting simultaneously (causing obstruction), hydrocephalus (enlarged head), or conjoined foetuses can all cause dystocia
There are a few signs of dystocia – from birthing that doesn’t happen within 24 hours of a drop in rectal temperature, to straining for one to two hours without producing a foetus, a longer than usual resting period between foetuses (< 6 hours), abnormal vaginal discharge, and signs of pain or illness in the bitch or queen. Dystocia can cause a medical emergency, so it is critical that veterinary treatment be sought before the condition puts the mother and foetuses at risk. Often the treatment of dystocia is caesarean section to help deliver the puppies or kittens.
Vaginitis
Inflammation of the vagina can affect puppies as well as mature dogs. Vaginitis is caused by a viral or bacterial infection, cancer or a foreign body stuck in the vagina (e.g. grass seeds or other environmental objects). Persistent licking of the vagina as well as unusual discharge may indicate the presence of vaginitis. The vet will perform a physical examination, ultrasound or endoscopy and other tests, and prescribe antibiotics to treat the infection. If there is a foreign body causing the vaginitis, it may need surgery to be removed.
Mammary tumour
A mammary tumour is the ‘breast cancer’ of dogs and cats, and is one of the most common types of tumours in dogs. It is more common in unspayed animals and is more frequently malignant than benign. Spaying the dog or cat before their second heat can prevent mammary tumours.
Mammary hypertrophy
Different to a mammary tumour, mammary hypertrophy is the overgrowth of mammary (breast) tissue in cats, which is benign. It is fairly common in young, oestrus-cycling queens, pregnant queens and non-neutered older cats. Mammary hypertrophy can also occur in non-neutered male cats that have been exposed to progesterone treatment. The vet will recommend spaying as the quickest treatment for the condition.
Vaginal prolapse or hyperplasia
The heat cycle in dogs – specifically during the peak of oestrogen secretion – can cause their vaginal tissue to swell. Sometimes this causes the internal vaginal tissue to prolapse outwards through the vulva, where it is vulnerable to injury and infection. It requires persistent cleaning and antibacterial treatment, and it’s advised that the dog wear an Elizabethan collar to prevent her from injuring herself. When oestrogen production decreases, it can resolve the hyperplasia and the dog’s vagina returns to normal. However, the condition will recur with each heat cycle. If it’s troublesome, the cure for vaginal hyperplasia is spaying.
Diagnosing and treating problems in the female reproductive system
If your dog or cat presents with problems with her reproductive system, consult with the vet immediately, as some of these diseases could be life-threatening. If your dog or cat has symptoms such as fever, vomiting, lethargy and lack of appetite, this could mean different things at different stages in your pet’s oestrus cycle. It is critically important to report any and all symptoms and especially when they started.
The vet will use diagnostic testing, urinalysis, X-rays and ultrasonography, and even surgical scoping to determine the cause of your pet’s illness. Vaginal and lactation cytology (smear) is necessary to determine the oestrus timeline as well as to identify infections. Fine needle aspiration and/or tumour biopsy can inform cancer diagnoses. The treatment will be determined by the severity of the disease and your pet’s health and physical condition.
Very often, treating reproductive issues can be most efficiently and effectively done by spaying the animal; eliminating recurrences and future problems by removing the organs that cause them. Unless you are a registered breeder of working or conformation animals, please do not breed your pets. It is a misconception – a total myth – that dogs and cats are better off, friendlier or calmer after they’ve had their first litter. There is no reason to casually breed your pets, especially in the wake of the pet overpopulation problem in South Africa and the subsequent unnecessary euthanasia of around a million dogs and cats due to a shortage of viable homes for them.
How to support your pet’s healthy female reproductive system
The best way to support your dog or cat’s healthy reproductive system is by having her spayed. Cats should be spayed by five months old, while small to medium dogs should be spayed by six months old. Large and giant breed dogs are slower to mature and may need more time to develop before being spayed – confirm the best time for your large or giant puppy’s spaying and ensure it is done before her first heat cycle.
Spaying your pets prevents:
- mammary and cervical cancer in dogs and cats
- uterine and ovarian cancers
- pyometra in dogs
- feline AIDS and feline leukaemia in cats, since she will not be in oestrus and will not attract unvaccinated strays
- cat fights (and the resulting trauma, injury and infection)
If your pet accidentally gets pregnant, or if you are fostering a pregnant female, protect her reproduction system with the appropriate nutrition and supplements to support her and her foetuses’ health. Notify the vet and ensure you have all of the available emergency phone numbers, especially when preparing for the birth of the litter.
Make sure you take your dog or cat for an annual health check-up with the veterinarian. If you have any concerns about your female pet’s reproduction system, be sure to raise these with the vet so they can check them out before any conditions arise. If you are reluctant to spay your pets, please discuss these concerns with the vet.
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