Pyometra is a condition that occurs in female, unspayed dogs, where their uterus becomes infected, leading to life-threatening illness. Middle-aged and older female dogs who have not been spayed are at risk for pyometra.

What causes it?

When a female dog is ready for pregnancy, her body will prevent immune system cells (i.e., white blood cells) from entering the uterus, because they would interfere with fertilization.

In addition, the lining of the female dog’s uterus will thicken for several weeks so her body is prepared to carry a litter. If pregnancy doesn’t occur, the lining of the uterus will get thicker and thicker during each of her fertile cycles (known as “heat”). Eventually, the lining will be so thick that cysts will form.

Also during this time, the muscles of the uterus and cervix (i.e., the entrance to the uterus) are weakened. A relaxed cervix is necessary for fertilization, but it also means that bacteria can enter more easily. Weakened muscles of the uterine wall means that bacteria can’t be expelled–normally, the uterus would be able to contract itself to expel infected fluid.

The combination of an absence of white blood cells, a lining covered in cysts, and weakened muscles creates the perfect environment for a severe bacterial infection—known as pyometra.

What are the signs?

If the dog’s cervix is still relaxed, there will be pus and abnormal discharge draining out. This is known as open pyometra.

If the cervix is closed, which is the more dangerous situation, the pus will accumulate and cause the dog’s abdomen to swell. This is called closed pyometra. This will cause severe symptoms very quickly, including weakness, vomiting, and diarrhea.

An increase in water consumption and urination is a symptom is both open and closed pyometra, because the body is trying to flush the toxins released by the bacterial infection.

How is the diagnosis made?

If there is discharge from the cervix or a bloated abdomen in an older female dog that has not been spayed, these are indicators that diagnostic tests should be done to confirm whether a dog has pyometra.

Diagnostics would include a blood test to look at the white blood cell count and level of globulins in the blood. A urine test would also be conducted, because normally the concentration of urine is low due to the dog drinking an abnormally large amount of water.

As for looking for structural abnormalities, an x-ray or ultrasound of the abdomen could be done to see if the uterus is enlarged. An ultrasound can also identify thickened uterine walls and the presence of fluid in the uterus.

What is the treatment?

If pyometra is not treated, and quickly, the bacteria in the uterus will produce toxins that will most likely be fatal to the dog. Additionally, in closed pyometra, the uterus may rupture and leak into the body, also causing death. It’s very important to immediately seek treatment for this condition if you suspect your dog may have it, especially because treatments are more effective the earlier the condition is diagnosed.

There are two treatments for pyometra: surgical and medical. In the surgical treatment, the uterus and ovaries are removed (also known as “spaying”). This procedure is more complex than spaying a dog who is in good health, because in most cases, infection has already weakened the dog significantly. Antibiotics and IV fluids are also administered to the dog when using this method.

The other approach for treating pyometra is the medical treatment. Usually, owners who are using the dog for breeding may opt for this method, because it doesn’t involve spaying the dog. In this treatment, the dog is given hormones, called prostaglandins, that relax the cervix and cause the uterine muscles to squeeze out infected pus.

The medical treatment for pyometra comes with numerous risks and it’s efficacy is not guaranteed. For open pyometra, it has a success rate of 75-90%, but for closed pyometra, the success rate is between 25-40%. Also, there is a high chance of reoccurrence for pyometra using this treatment—about 50-75%. Moreover, the chance of successfully breeding the dog after it recovers is reduced to 50-75%.