Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066





The word “pyometra” is derived from Latin “pyo” meaning pus and “metra” meaning uterus. The pyometra is an abscessed, pus-filled infected uterus. Toxins and bacteria leak across the uterine walls and into the bloodstream causing life-threatening toxic effects. The uterus itself dies releasing large amounts of pus and dead tissue into the abdomen. Without treatment, death is inevitable. Prevention of this disease is one of the main reasons for routinely spaying female dogs.


(original graphic by

Pus-filled uterus after removal from a small dog
Pus-filled uterus after removal from a small dog.
(original graphic by




Classically, the patient is an older female dog. Usually, she has finished a heat cycle in the previous 1-2 months. She has a poor appetite and may be vomiting or drinking an excessive amount of water. There are two forms of pyometra: "open" and "closed, with open being the most common. With an open pyometra, the cervix is open allowing for pus to drain outside the body. Because the pus is can drain, the patient is usually not as sick plus with the noticeable smelly vaginal discharge, the patient will likely be seen by the vet sooner. With a closed pyometra, the cervix is closed and the toxic pus is held within the body. Diagnosis is trickier without the obvious discharge and the patient will be sicker from the toxins.



Closed Pyometra

A radiograph showing a closed pyometra. The large outlined structure is the pus-filled uterus.
A normal uterus is too small to be seen on a radiograph.

(Radiograph thanks to Alta Mesa Animal Hospital)

Fever, appetite loss, and vaginal discharge in an unspayed older female dog makes pyometra a likely diagnosis. Lab work shows a pattern typical of widespread infection which is often helpful in narrowing down the diagnosis. Radiographs may show a gigantic distended uterus though sometimes this is not obvious and ultrasound is needed to confirm the diagnosis.



With each heat cycle, the uterine lining engorges in preparation for pregnancy. Eventually, some tissue engorgement becomes excessive or persistent (a condition called “cystic endometrial hyperplasia”). This lush glandular tissue is ripe for infection (recall that while the inside of the uterus is sterile, the vagina below is loaded with bacteria). Normally, between the closed cervix and the immune system, the bacteria of the vagina are held at bay but during this particular phase of the heat cycle, the bacteria may be able to ascend and cause the pyometra infection. Hormonal effects on the uterine tissue accumulate with each heat cycle which means pyometra is much more common in older females as they have experienced many hormonal cycles.



The usual treatment for pyometra is surgical removal of the uterus and ovaries. It is crucial that the infected uterine contents do not spill and that no excess hemorrhage occurs. The surgery is challenging especially if the patient is toxic. Antibiotics are given at the time of surgery and may or may not be continued after the uterus is removed. Pain relievers are often needed post-operatively. A few days of hospitalization are typically needed after the surgery is performed.

It is especially important that the ovaries be removed to prevent future hormonal influence on any small stumps of uterus that might be left behind. If any portion of ovary is left, the patient will continue to experience heat cycles and be vulnerable to recurrence.

While the end result of pyometra surgery is a spayed dog, there is nothing routine about a pyometra spay. As noted, the surgery is challenging and the patient is in a life-threatening situation. Intravenous fluid support during and after surgery are generally needed plus the patient is toxic and requires extra support. The uterus is very large and the associated blood vessels are engorged making the surgery time longer. Recovery from surgery takes longer compared to the spay of the healthy female dog. For these reasons, the pyometra spay typically costs five to ten times as much as a routine spay.



  • The infected uterus is resolved rapidly (in an hour or two of surgery).
  • Extremely limited possibility of disease recurrence.



  • Surgery must be performed on a patient that could be unstable.



In the late 1980’s another treatment protocol became available that might be able to spare a valuable animal’s reproductive capacity. Here, special hormones called “prostaglandins” are given as injections to cause the uterus to contract and expel its pus. A week or so of hospitalization is necessary and some cramping discomfort is often experienced. This form of treatment is not an option in the event of a “closed” pyometra (because the closed cervix prevents drainage of the infected material even in the face of prostaglandin contractions). Further, the dog must be bred on the next heat cycle. If she is not bred or does not conceive puppies on the next heat cycle, the recurrence rate of pyometra may be as high as 77%. After recovery from pyometra, the uterus is damaged and may not carry a litter normally (pregnancy rates are only 50-65%). Unless the dog has great value to a breeding program, it may not be worth it to attempt prostaglandin treatment.



  • There is a possibility of future pregnancy for the patient (though it is possible that there will be too much uterine scarring).
  • Surgery can be avoided in a patient with concurrent problems that pose extra anesthetic risk.



  • Pyometra can recur.
  • The disease is resolved more slowly (over a week or so).
  • There is a possibility of uterine rupture with the contractions. This would cause peritonitis and escalates the life-threatening nature of the disease.
  • Breeding should occur on the very next heat cycle.



Spaying represents complete prevention for this condition. The importance of spaying cannot be over-emphasized. Often an owner plans to breed their pet or is undecided, time passes, and then they fear she is too old to be spayed. The female dog or cat can benefit from spaying at any age. The best approach is to figure that pyometra is highly likely to occur if the female pet is left unspayed; any perceived risks of surgery are very much out-weighed by the risk of pyometra.


Female cats may also fall victim to pyometra. In the cat, the disease is just as serious and the treatment options are the same. There is an important difference for cats with pyometra, however: female cats rarely appear sick until very late stages of the disease. The classic creamy vaginal discharge is present and often the belly appears distended because of the size of the pus-filled uterus but the cat herself is generally eating and grooming as if nothing is much is going on. If the female cat is fastidious and cleans away the discharge, the pet owner may wrongly conclude that she is simply pregnant. Unfortunately, this lack of apparent illness leads to a delay in diagnosis and this delay can be lethal.

As with dogs, diagnosis is usually by radiography though ultrasound can be used particularly if radiography is ambiguous. Treatment for cats is similar to treatment for dogs: surgery is traditional but prostaglandins may be used if it is important to preserve the cat's ability to breed.

black and white cat mf



After a pet is spayed, there is frequently a small stump of uterine tissue inside the abdomen where the tract has been tied off. As long as there are no female hormones in play, this small stump will be inactive and cannot develop a pyometra. If, on the other hand, there are hormones in circulation, a pyometra can develop in the stump. Symptoms are similar to those for a uterine pyometra, (vaginal discharge, fever etc.) except that the patient has been spayed sometimes years prior.

Treatment is surgical removal of the infected stump but the real problem is the source of estrogen or progesterone that was necessary to create the condition in the first place. This source of hormone must be identified. Sometimes a small portion of ovary is left behind or even re-grows spontaneously after spaying creating what is called ovarian remnant syndrome. Alternatively, there are many estrogen-containing topical products for human use to which a pet can become exposed through licking or cuddling. Occasionally, progestins are used in cats to control skin disease though these have generally been supplanted by newer medications.

Stump pyometra is suspected when a mass is seen on radiographs or ultrasound in the area of the uterine stump and there are accompanying clinical signs of pyometra. If surgery ensues to remove the stump and there is no obvious exposure to a hormone-containing product, the area of the ovaries is explored for evidence of ovarian remnant. If no remnant is visible, sometimes biopsies are taken to rule out microscopic remnants. Once the hormone source is gone, there should be no further pyometra risk.

Page last updated: 2/26/2024