Pyometra is relatively uncommon in cats compared to dogs. About 2.2% of intact female cats develop pyometra by age 13, while roughly 20% of intact female dogs develop it by age 10. The difference comes down to how cats reproduce: they only ovulate when they mate, which means their uteruses spend far less time exposed to the hormone that sets the stage for infection.
How the Numbers Compare to Dogs
A large Swedish insurance database study found a mean incidence of about 17 cases per 10,000 cat-years at risk. That’s a useful way of expressing risk over time, but the simpler figure is more intuitive: over a full lifespan, roughly 1 in 45 intact female cats will develop the condition. In dogs, the lifetime risk is nearly ten times higher.
The reason for this gap is biological. Cats are induced ovulators, meaning they typically release eggs only after mating. Without ovulation, their bodies don’t produce sustained high levels of progesterone, the hormone that makes the uterus vulnerable to infection. Dogs, by contrast, go through a progesterone-heavy phase after every heat cycle whether they mate or not. Cats also have a shorter non-pregnant hormonal phase (about 40 days), which further limits their exposure window.
Age and When Risk Climbs
Pyometra can technically strike at any age. Cases have been documented in cats as young as 10 months. But risk rises steadily with age, and the sharpest increase happens after age 7. The average age at diagnosis is around 4 years, reflecting a wide spread that skews older.
In one clinical study of 52 confirmed cases, about 27% of affected cats were younger than 1.5 years and 40% were older. The remaining cases fell into an unclassified middle range. The takeaway: younger cats aren’t immune, but the longer an intact female goes through repeated heat cycles, the more cumulative hormonal exposure her uterus accumulates, and the higher her risk becomes.
Breeds With Higher Risk
Not all cats face equal odds. The Swedish study found a dramatic breed effect. Sphynx cats had the highest incidence by a wide margin, at 433 cases per 10,000 cat-years at risk, roughly 25 times the overall average. Several other breeds also showed elevated rates (above 60 per 10,000 cat-years): Siberian, Ocicat, Korat, Siamese, Ragdoll, Maine Coon, and Bengal. If you have an intact female of one of these breeds, pyometra is a more realistic concern than the 2.2% lifetime average suggests.
What Happens Inside the Uterus
Pyometra develops when hormonal changes create conditions that favor bacterial growth inside the uterus. During a heat cycle, estrogen causes the cervix to open and the uterine lining to thicken. After heat ends, progesterone takes over. It closes the cervix, reduces the uterus’s ability to contract and clear bacteria, suppresses the local immune response, and increases glandular secretions inside the uterine lining. The result is a warm, sealed, nutrient-rich environment with weakened defenses.
The bacterium most commonly responsible is a specific strain of E. coli that also causes urinary tract infections. It migrates from the lower reproductive or urinary tract into the uterus and multiplies rapidly in the progesterone-altered environment. The uterus fills with pus, sometimes dramatically. Cats with pyometra often show lethargy, loss of appetite, vomiting, a swollen abdomen, and sometimes a foul-smelling vaginal discharge (though in “closed” pyometra, where the cervix stays sealed, there may be no visible discharge at all, making it harder to detect).
Hormonal Medications Raise the Risk
Synthetic progesterone-like drugs, sometimes used to suppress heat cycles in breeding cats, significantly increase pyometra risk. In one long-term study tracking queens given a specific progestin weekly over several years, 11% developed vaginal discharge or pyometra after 6 years of treatment, and 38% did after 8 years. These drugs mimic exactly the hormonal conditions that make the uterus vulnerable, and prolonged use compounds the effect. Inappropriate or unsupervised use of hormonal medications is a well-documented trigger for pyometra in younger cats who would otherwise be at low risk.
Treatment and Survival Rates
The standard treatment is surgical removal of the uterus and ovaries, and the outcomes are excellent. In one study of 126 cats treated surgically, the survival-to-discharge rate was 100%. About a third of those cats needed two or more nights of hospitalization, and 4% had uterine rupture, a serious complication that required emergency care but was still survivable in that group.
The overall mortality rate across all cats diagnosed with pyometra, including those who were too sick for surgery or were euthanized, is around 6%. That’s slightly higher than the 4% mortality reported in dogs with pyometra, likely because cats are better at hiding illness and may not be brought in until the infection is advanced. Medical (non-surgical) treatment exists but is rarely used in cats. In the same study, only 2 out of 134 cats received medical management, while 6 were euthanized without treatment.
Can Spayed Cats Get Pyometra?
It’s rare, but yes. A condition called stump pyometra can develop if a small piece of uterine tissue is left behind during spay surgery, particularly if ovarian tissue also remains. The leftover ovarian cells continue producing hormones, and the uterine stump can become infected through the same mechanism as standard pyometra. Stump pyometra can also be triggered by external progesterone-type medications given to a spayed cat. It’s uncommon enough to appear mainly as individual case reports rather than large studies, but it’s worth knowing about if a spayed cat develops signs like vaginal discharge, lethargy, or unexplained fever.