Pyometra is a bacterial infection that fills the uterus with pus, and it affects unspayed females, usually in the weeks after a heat cycle. Drinking and urinating more, vomiting, lethargy, a swollen belly or any vaginal discharge in an unspayed female is an emergency. It does not resolve on its own and it worsens quickly.
Why this one catches families off guard
Pyometra rarely announces itself the way an injury does. There is no wound, no limp and no obvious moment when something went wrong. What owners usually describe is a dog who has been a bit quiet for a couple of days, is drinking more than usual, and has gone off her breakfast.
Those signs are easy to attribute to warm weather or a mild upset stomach. Meanwhile the uterus is filling, and the infection is releasing toxins into the bloodstream. By the time a dog looks genuinely unwell, this has often been developing for several days.
The other reason it surprises people is timing. It typically appears two to eight weeks after a season, when the heat itself is over and forgotten and nobody is thinking about the reproductive system any more.
What is actually happening
After a heat cycle, hormonal changes thicken the lining of the uterus and the cervix stays open for a period. That combination gives bacteria an opportunity to enter and establish themselves in an environment that suits them.
The uterus fills with infected material. Because the wall of the uterus is stretched and inflamed, and because the infection is producing toxins that the body absorbs, this is a whole-body illness rather than a local problem. It affects the kidneys, the circulation and the ability to regulate fluid, which is why affected dogs become so thirsty.
The risk rises with each season, so an older unspayed female who has had many cycles is at higher risk than a young one. It is common enough that any unspayed female with vague illness should be considered for it rather than treated for a stomach upset.
Open and closed: the distinction that matters most
In an open pyometra the cervix remains open, so infected material drains out. Owners notice a discharge from the vulva, often thick and unpleasant smelling, sometimes blood-tinged or creamy, and frequently spotted on bedding or the floor rather than on the dog. Dogs with an open pyometra often lick more than usual, which can hide the discharge entirely.
In a closed pyometra the cervix is shut and nothing escapes. That sounds tidier and is in fact considerably more dangerous. The uterus continues to fill with nowhere to drain, the abdomen may swell, the dog becomes ill faster, and there is a risk of the uterus rupturing and spilling infected material into the abdomen.
The practical consequence is important: the absence of discharge is not reassuring. The sicker dog is often the one with nothing to see.
The signs to act on
- Drinking noticeably more, and urinating more or having accidents indoors
- Lethargy, or a dog who is simply not herself
- Reduced appetite or refusing food entirely
- Vomiting or diarrhoea
- Any discharge from the vulva, particularly if thick, discoloured or foul smelling
- A swollen, tense or painful abdomen
- Excessive licking of the back end
- Panting, restlessness, or a reluctance to lie down comfortably
- Pale gums, weakness or collapse in advanced cases
Increased thirst in an unspayed female who has had a season in the past two months deserves a phone call on its own, even with nothing else wrong. It is one of the earliest and most reliable signals, and it is the one owners most often notice first and dismiss.
Cats too, though less often
Unspayed queens develop pyometra as well. It is less common than in dogs, partly because of how feline ovulation works, and cats are considerably better at hiding it. A cat is more likely to present simply as quiet, off her food and dehydrated, with no discharge and no obvious abdominal swelling. Any unspayed female cat who becomes unwell without explanation should have this on the list.
What happens at the clinic
Assessment usually starts with a physical examination and bloodwork looking at white cell counts, kidney values and hydration, alongside imaging to look at the uterus. Ultrasound and radiographs both have a role, and imaging is what confirms a fluid-filled uterus rather than another cause of a swollen abdomen. That work runs through our diagnostic services.
The standard treatment is surgical removal of the infected uterus and ovaries, together with intravenous fluids, pain relief and antibiotics. This is not the same procedure as a routine spay, despite involving the same organs. The patient is unwell, the tissue is fragile and distended, and the surgery carries the risks that come with operating on a sick animal rather than a healthy one. It is handled by our surgical services team with support from urgent care.
Medical management without surgery exists in a narrow set of circumstances, generally involving a valuable breeding female with an open pyometra who is not yet seriously ill. It carries a real risk of recurrence at the next cycle and is not appropriate for most patients. Your veterinarian will explain whether it is even an option in your dog’s case.
Delay is the factor that changes outcomes most. A dog treated early is in a very different position from one who has been unwell for a week, which is the entire argument for calling on the first day of increased thirst rather than the fourth.
Prevention is straightforward
Spaying removes the uterus and ovaries and therefore removes the possibility of pyometra. That is the whole prevention story, and it is why the procedure is discussed as a health decision rather than only a population one. Our post on spay and neuter services covers what the routine procedure involves.
Timing is an individual conversation. Breed, size, age and lifestyle all feed into when spaying is appropriate for a particular dog, and there are genuine considerations on both sides for some breeds. That discussion belongs in a medical consultation rather than in a blanket rule.
If you have chosen to keep a female entire, whether for breeding or for another reason, the practical step is to keep a record of her seasons and to treat the eight weeks afterward as a period of raised awareness. Note the date each heat starts. Being able to tell a veterinary team “she finished her season five weeks ago” changes how quickly the right question gets asked.
Older unspayed females benefit from regular monitoring generally, which is covered in our guide to wellness for senior dogs and cats in Kitsilano and supported through our wellness program. When you cannot judge how urgent a situation is, our guide to urgent pet care sets out the thresholds.
Frequently asked questions
How quickly does pyometra become dangerous?
It can progress from vague signs to a critical illness within a few days, and a closed pyometra moves faster than an open one. Because the infection releases toxins that affect the kidneys and circulation, a dog can look mildly unwell in the morning and be seriously ill by the following day. Treat increased thirst after a recent season as a same-day concern.
Can pyometra be treated without surgery?
Only in a narrow set of cases, generally an open pyometra in a breeding female who is not yet seriously ill. It carries a significant risk of the infection returning at the next cycle and is not suitable for most patients. Surgical removal of the uterus and ovaries is the standard treatment and it also prevents recurrence.
My dog has no discharge, so is she in the clear?
No, and this is the most dangerous misunderstanding about this condition. In a closed pyometra the cervix is shut, so nothing drains out at all. Those dogs typically become ill faster and carry the added risk of the uterus rupturing. Absence of discharge should never be taken as reassurance in an unwell unspayed female.
When after a heat cycle does pyometra usually appear?
Most commonly between two and eight weeks after a season ends, which is exactly when owners have stopped thinking about it. Keep a note of when each heat begins, and treat the two months afterward as the window in which increased thirst, reduced appetite or lethargy warrants a call rather than a wait.
Does spaying completely prevent it?
A full spay removes the uterus and ovaries and therefore removes the risk. Very rarely, a small remnant of uterine tissue left behind at surgery can become infected, which is called a stump pyometra, but this is uncommon. For practical purposes, spaying is the prevention.
Can cats get pyometra?
Yes, though less frequently than dogs. Cats also hide it better, so an affected queen may show nothing more specific than lethargy, poor appetite and dehydration, often with no discharge and no obvious swelling. Any unspayed female cat who becomes unwell without a clear explanation should be assessed with this possibility in mind.