Pyometra occurs in unspayed female cats and dogs when hormones cause the uterine lining to thicken and form cysts, creating an ideal breeding ground for bacteria that ascend from the vagina, and resulting in a potentially life-threatening infection. Symptoms include general malaise and, in some cases, a foul vaginal discharge. Emergency surgical removal of the uterus and ovaries is typically considered the best treatment.


Pyometra is a severe bacterial infection of the uterus that can be potentially life threatening.

When a pet is in heat, the dominant hormone affecting the uterus is estrogen. At the end of the heat cycle, estrogen levels drop and progesterone (another hormone) levels rise. Over the course of several heat cycles, progesterone can cause changes in the uterine lining, such as thickened tissue and cysts. This creates the ideal environment for bacteria to flourish.

Pyometra occurs when bacteria ascend from the vagina into the uterus and multiply. The body attempts to fight off the infection by sending white blood cells to the uterus, which creates the fluid buildup.

Pyometra is described as being “open” or “closed.” With “open” pyometra, the cervix (the portion of the uterus that connects with the vagina) is open. The fluid that forms in the uterus as a result of the infection can drain through the vagina out of the body.

When the cervix is closed, as in “closed” pyometra, the fluid in the uterus cannot drain through the vagina, so it builds up, stretching the uterine walls and potentially rupturing the organ. If this occurs, the infection spreads to the abdomen (peritonitis) and possibly into the bloodstream (septicemia), leading to shock and, often, death.

The condition is most common in older, unspayed female dogs that have never had a litter, but it can occur in any female dog or cat that has not been spayed. In dogs, pyometra is most likely to happen in the first few weeks to months after a heat cycle.

Treatment with estrogen for other conditions (such as ending an unwanted pregnancy) can also predispose a pet to pyometra. Because of this potential side effect, this practice has fallen out of favor in the past few years.

Affected Breeds

There is no known breed predisposition for pyometra.

Symptoms and Identification

Pets that have open pyometra may have a foul-smelling white, yellow, or blood-tinged discharge from the vagina. Otherwise, the signs can be somewhat vague, such as:

  • Lethargy (tiredness)
  • Loss of appetite
  • Vomiting
  • Increased drinking and urinating
  • Abdominal distention (swelling)
  • Fever is not always present, as it is with most bacterial infections
Your veterinarian will most likely recommend bloodwork and abdominal radiographs (X-rays) to visualize the uterus. Occasionally, an abdominal ultrasound may be needed to get a better view of the uterus. If your pet has a vaginal discharge, your veterinarian may examine the discharge under a microscope for signs of infection.


Surgical removal of the uterus and ovaries is the best treatment for pyometra. In most cases, this is an emergency surgery that must be performed before the uterus ruptures or the infection spreads to other parts of the body. Because it is a more complicated surgery than a typical spay in a healthy animal, it will most likely be more expensive. The pet may also need intravenous fluids and antibiotics.

If the pet is a valuable breeding animal, and she has open pyometra, it may be possible to administer special hormones to shrink the uterus back to size and avoid surgery. However, these medications can have serious side effects, and the risk of pyometra recurring is high.


Early spaying of female pets prevents pyometra.

This article has been reviewed by a Veterinarian.