Pyometra is defined as an infection of the uterus, and it is considered a serious, life-threatening condition, which is why it must be treated quickly and aggressively.

Pyometra is a secondary infection that occurs as a result of hormonal changes in the female dog’s reproductive tract. During the “heat“ cycle, the white blood cells, which normally protect against infection, are prevented from entering the uterus. That allows sperm to freely enter the female’s reproductive tract, without being damaged or destroyed by these immune system cells.

After the heat cycle, progesterone levels remain elevated for up to two months, causing the thickening of the uterus lining to prepare it for pregnancy and fetal development. If pregnancy doesn’t occur after several heat cycles, the thickening of the uterus lining continues until cysts form within the tissue.

These thickened cysts secrete fluids that create an ideal environment for bacterial growth. Apart from that, the high progesterone levels prevent the muscles of the uterus lining from expelling accumulated fluids or bacteria. The combination of these factors usually leads to an infection.

Bacteria enter the uterus if the cervix is open and relaxed. A thickened or cystic uterine wall is the perfect condition for bacterial growth, which is why the muscles of the uterus cannot contract properly due to the thickening of the uterine wall or hormones such as progesterone. This means that the bacteria cannot be expelled.

Pyometra can occur in any dog that has had several heat cycles, but has remained sexually intact, but it’s most commonly found in older female dogs. It usually occurs 2-8 weeks after the last heat cycle.

The clinical signs depend on whether the cervix is open or not. If it’s open, there will be pus coming out of the uterus through the vagina to the outside. A large amount of pus can be observed on the skin and hair under the tail, or at the place in the house where the dog’s spent the most time. Fever, lethargy, anorexia and depression may sometimes occur.

If, however, the cervix is closed, the pus will not come outside, but it will build up inside the uterus, causing the dog’s stomach to look bloated. The bacteria will then release toxins into the bloodstream, and dogs with closed pyometra will fall ill very quickly. They will become depressed, and other symptoms can appear, too, such as diarrhoea or vomiting.

The toxins released by the bacteria affect the ability of the kidneys to retain fluids, which is why increased urine production may occur. Many dogs then drink a lot of fluids to make up for it.

If your dog happens to have pyometra, the best treatment would be to surgically remove the infected uterus and ovaries, meaning, to spay the dog. All dogs with pyometra in the early stage are excellent surgical candidates, whereas those with the disease in the latter phase require longer vet care. If pyometra isn’t treated, the consequences can, unfortunately, be fatal.

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