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Cornell Richard P. Riney Canine Health Center

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Pyometra is a serious and potentially life-threatening infection of the uterus that causes it to fill with bacteria and pus. Many dogs with a pyometra have vaginal discharge and may feel very sick with a poor appetite, lethargy, vomiting and sometimes increased thirst or urination. The most effective treatment for pyometra is surgery to remove the uterus and ovaries, also known as a spay or ovariohysterectomy. Any female dog that has not been spayed can develop a pyometra, but they are more common in middle-aged to older female dogs who have been through multiple heat cycles. Most dogs have a good prognosis if diagnosed and treated promptly, but it can be deadly if left untreated. Pyometra can be easily prevented by spaying at a young and healthy age.


Pyometra is caused by hormonal changes and, most commonly, the bacteria E. coli that can ascend from the vagina into the uterus. This typically occurs during a dog’s estrus (heat cycle) when the cervix is more relaxed. Often, a dog will develop a pyometra one to two months after their previous heat cycle. Dogs enter the diestrus stage after a heat cycle, which causes the hormone progesterone to increase. Progesterone causes the uterus lining to thicken. After numerous heat cycles in a dog’s life, the lining can develop cysts called cystic endometrial hyperplasia (CEH), which leads to fluid secretions, making it easier for bacteria to grow. As the uterus fills with bacteria and pus, the toxins formed by the bacteria can leak from the uterus and enter the bloodstream, leading to life-threatening effects.

Less commonly, if a dog was spayed but not all the ovarian tissue was removed, a dog could develop a condition called stump pyometra, where the residual uterine tissue develops an infection. All ovarian tissue must be removed to prevent heat cycles and eliminate the risk of any form of pyometra.

Clinical Signs

The severity of signs of a pyometra will depend on whether the cervix (entrance into the uterus) is open or closed. More severe signs of illness will occur when the cervix is closed. Vaginal discharge that is cream-colored or bloody is the primary sign when the cervix is open, but they may still show signs of systemic illness.

  • Vaginal discharge
  • Lethargy
  • Poor appetite
  • Increase thirst and urination
  • Distended or painful belly
  • Vomiting
  • Fever
  • Pale gums
  • Weakness or collapse


Your veterinarian will diagnose a pyometra based on physical exam findings, such as vaginal discharge and a history of a recent heat cycle. Your veterinarian may also use any of the following tests to confirm a diagnosis:

  • Ultrasound or X-rays to identify an enlarged, fluid-filled uterus
  • Blood work
  • Urine sample
  • Vaginal cytology


A pyometra is a medical emergency that requires prompt treatment. The mainstay of treatment includes:

  • IV fluids
  • Antibiotics
  • Ovariohysterectomy

Pyometra is best treated with surgery to remove the ovaries and uterus (spay). The surgery for a pyometra is often more complicated than a spay for a normal, healthy dog. Some dogs may require more intensive care and monitoring for signs of sepsis, dehydration, shock, anemia and more.

Medical management involves injections of the hormone prostaglandin, fluids and antibiotics. However, it is rarely considered and generally discouraged except for specific cases, such as a young, valuable breeding dog. It is not a viable option for a critically ill dog or one with a closed pyometra. Medical management takes several days before showing improvement, and some may not improve at all and may ultimately require surgery. Additionally, medical management has many side effects, including panting, drooling, diarrhea, vomiting and even the potential rupture of the uterus, which could be life-threatening.


Untreated pyometra can be deadly from overwhelming infection and sepsis. However, most patients have a good prognosis when diagnosed and treated with surgery early. Dogs that develop sepsis or have a ruptured uterus often have a worse prognosis. Dogs that are treated medically often experience a recurrence of infection.


Pyometra is entirely preventable if a dog is spayed before the development of infection in the uterus. A spay to remove the ovaries and uterus is recommended to prevent pyometra. If a dog is intended for breeding, they should be bred at the appropriate age to minimize their risk of developing a pyometra. Having your dog spayed while young and healthy is safer and less costly than waiting for an emergency pyometra spay.