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Uterine infection in dogs

Written by Mara | January 15, 2026

A uterine infection in dogs (pyometra) is a serious and potentially life-threatening condition that mainly occurs in unspayed female dogs. It often develops a few weeks after a season and requires quick recognition and treatment. In this blog, you’ll read how a uterine infection develops, which signs you may notice, how the diagnosis is made, and how you can help prevent it.

What is a uterine infection?

With a uterine infection, the uterus fills with pus as a result of a bacterial infection. Due to hormonal influences during the cycle, the uterine wall becomes thicker and resistance decreases, allowing bacteria to multiply more easily.

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The dog’s cycle and the risk of a uterine infection

The cycle of a female dog plays an important role in the development of a uterine infection. During and after a season, the hormone balance changes considerably. After a season, the hormone progesterone predominates, which ensures that:

the uterine wall thickens
the cervix stays closed
the natural defences in the uterus decrease

These conditions make the uterus extra susceptible to infections. About 2 months after a season is the period with the highest risk of developing a uterine infection.

You can read more about seasons in our blog What do you need to know about heat in dogs.

What signs can you see with a uterine infection?

The symptoms can vary and may be vague at first. Common signs include:

tiredness and lethargy
reduced appetite
drinking and urinating more
fever
vomiting or diarrhoea
abdominal pain or a swollen abdomen

With an open uterine infection, a pus-like or bloody discharge from the vulva may be visible.

With a closed uterine infection, this discharge is absent, so the condition is often recognised later. This makes this form especially dangerous. The pus cannot drain away, which puts the uterus under pressure and it can rupture. There is also a greater chance that bacteria enter the bloodstream through the uterine wall and cause sepsis and other problems.

How is the diagnosis made?

The vet makes the diagnosis based on:

history (has the dog recently been in season?)
physical examination
blood tests (inflammation markers, kidney function)
an abdominal ultrasound to visualise the enlarged, pus-filled uterus

Acting quickly is crucial to prevent complications.

Treatment of a uterine infection in dogs

A uterine infection in a dog is an emergency!

The treatment of choice is almost always surgery, where the uterus and ovaries are removed (spaying). This is often an emergency procedure. A dog is frequently supported at the same time with intravenous fluids to help remove waste products. This route also allows anti-inflammatory medication and antibiotics to be administered effectively.

In some exceptional cases, for example in breeding bitches with an open uterine infection, medical treatment may be considered. However, this carries risks and requires intensive supervision by the vet.

Uterine infection after pregnancy

A uterine infection can also develop after pregnancy. After giving birth, the uterus is vulnerable and retained tissue or reduced contraction can lead to infection. Signs can be similar to those of a regular uterine infection and often occur in the weeks after whelping.

You can read more about pregnancy in dogs in our blog Dog pregnancy.

Spaying as prevention

Spaying is the most effective way to prevent a uterine infection. By removing at least the ovaries:

the influence of hormones disappears
the risk of other conditions, such as mammary tumours, is also reduced

It is not even necessary to remove the uterus as well. In an older dog, or if the uterus does not look healthy, it may be decided to remove the uterus too.

In most cases, it is advised to spay about 3 months after the first season, once the reproductive organs have settled again.

More information can be found in our blog: Having your dog neutered or spayed.

A uterine infection in dogs is a serious condition. Because symptoms can sometimes be vague, it is important to take changes in behaviour or health in your female dog seriously, especially in the weeks after a season or after pregnancy. If in doubt, always contact your vet.

Read our other blogs too

What do you need to know about heat in dogs?

You brought your new puppy and it is a female. But what about when she is in heat? And how do I recognize it? How long does it take? What should I do during the heat? Can I prevent it? And what should I do if she accidentally mates? These are all questions that may come to mind when it comes to heat in a dog. We will answer your questions, so read on!

Having Your Dog Neutered or Spayed?

Neutering and spaying are terms often used interchangeably when it comes to rendering your dog infertile. But what’s the actual difference? And what are the pros and cons of these procedures? You’ll read all about it in this blog article!

Dog pregnancy

A female dog will come into heat an average of twice per year. On average, your dog will be in heat for about 3 weeks. This will be marked by vaginal discharge and swelling of the vulva. Generally speaking, a female dog will be fertile around the 10th day of being in heat. However, the duration of the heat and the point of fertility can vary greatly for every dog.

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About the author

Mara van Brussel-Broere, Veterinarian at Vetsend

Graduated as a companion animal veterinarian from Utrecht University, she uses her practical experience to advise customers and share knowledge at Vetsend. She finds it important to provide pet owners with clear information about health and wellbeing.