Pyometra is a potentially life-threatening infection of the uterus that mainly affects unspayed female dogs and cats. The condition can initially cause subtle changes, such as drinking more, eating less or becoming quieter than usual. Without prompt veterinary treatment, pyometra can progress to sepsis, organ dysfunction, shock and death.
Understanding the warning signs can help owners seek veterinary care before the infection becomes severe.
Veterinary review: Dr. Stylianos
Last reviewed: September 2026
What Is Pyometra?
Pyometra is a bacterial infection of the uterus. During the infection, inflammatory fluid and pus accumulate inside the uterus.
The name comes from the Greek words pyo, meaning pus, and metra, meaning uterus.
Both dogs and cats can develop pyometra. It mainly affects females that have not been spayed and still have functioning ovarian tissue.
Pyometra is more than a local uterine infection. Severe cases can cause systemic inflammation, sepsis, organ dysfunction and shock.
Without appropriate treatment, pyometra can be fatal.
Why Does Pyometra Happen?
Pyometra develops through an interaction between hormonal changes and bacterial infection.
The reproductive cycle is slightly different in dogs and cats, but hormones play an important role in making the uterus more susceptible to infection.
Pyometra in Dogs
After a female dog goes through heat, she enters a stage called diestrus. During this period, progesterone remains elevated whether or not pregnancy has occurred.
Progesterone causes several changes in the reproductive tract.
The glands in the uterine lining become more active and produce additional secretions. At the same time, the muscles of the uterus become less active, the cervix closes and local immune defences change.
These changes help prepare the uterus for pregnancy. However, they can also create favourable conditions for bacterial growth.
Bacteria can enter through the vagina and move upwards into the uterus. When bacteria are present during a progesterone-dominated phase, infection can develop.
Repeated reproductive cycles can also cause changes to the uterine lining.
One such change is called cystic endometrial hyperplasia (CEH). The uterine lining becomes thicker, while the glands within it can become enlarged and cystic.
CEH does not automatically cause pyometra. However, these changes can make the uterus more susceptible to infection.
Pyometra in Cats
Cats can also develop pyometra because hormonal changes can create conditions that allow bacteria to infect the uterus.
The feline reproductive cycle differs from the canine cycle. Female cats are induced ovulators, meaning ovulation is usually triggered by mating or hormonal stimulation rather than occurring automatically after every heat cycle.
When ovulation occurs, progesterone rises. This hormonal environment can contribute to changes within the uterus that make infection more likely.
Cats that receive certain hormonal medications may also have an increased risk of reproductive tract problems.
Although pyometra is less commonly diagnosed in cats than in dogs, it can still become a serious and potentially life-threatening disease.
An unspayed female cat should not be considered safe from pyometra simply because the condition is less common in cats.
Can a Young Dog or Cat Get Pyometra?
Yes.
Pyometra is more commonly associated with adult and older intact females, but young animals can also develop the disease.
Dogs
Older intact female dogs have a greater risk because their uterus has experienced repeated reproductive cycles over many years.
However, veterinarians can occasionally diagnose pyometra in relatively young dogs. Very unusual cases can even occur after only a small number of heat cycles.
Age should therefore never be used to completely rule out pyometra.
Dogs also do not experience menopause in the same way humans do. An older intact female can continue to experience reproductive cycles and remain at risk.
Cats
Young cats can also develop pyometra, although the disease is more often recognised in mature intact females.
Previous reproductive history does not provide complete protection. A cat does not need to have had kittens before she can develop pyometra.
For both species, being young does not completely eliminate the risk.
Open vs. Closed Pyometra
Veterinarians make an important distinction between open and closed pyometra.
The difference is whether the cervix remains open.
Open Pyometra in Dogs and Cats
With open pyometra, the cervix remains open. Infected material can therefore drain from the uterus through the vagina.
Owners may notice:
- Creamy discharge
- Yellow discharge
- Brown discharge
- Blood-tinged discharge
- Thick or pus-like discharge
- Increased licking around the vulva
Vaginal discharge can be one of the first visible signs.
However, discharge is not always present or easy for an owner to notice.
Cats in particular are often fastidious groomers. A cat may clean away vaginal discharge before an owner ever sees it.
Closed Pyometra in Dogs and Cats
Closed pyometra occurs when the cervix remains closed.
Infected material cannot drain normally, so it accumulates inside the uterus.
The uterus may become greatly enlarged and contain a significant amount of infected material.
This can make closed pyometra particularly dangerous.
Some dogs and cats with closed pyometra have no visible vaginal discharge at all.
No discharge does not rule out pyometra.
Closed pyometra can progress rapidly. Severe complications can include uterine rupture, abdominal contamination, sepsis and shock.
What Are the Symptoms of Pyometra?
Dogs and cats can develop many of the same symptoms, but there are important differences in how easily owners notice them.
Common signs include:
- Lethargy or depression
- Reduced appetite
- Refusing food
- Increased thirst
- Increased urination
- Vomiting
- Diarrhoea
- Abdominal enlargement
- Abdominal discomfort
- Fever
- Vaginal discharge
- Weakness
Symptoms of Pyometra in Dogs
Dogs may initially show relatively subtle changes.
An owner might notice that a previously healthy dog:
- Drinks more water
- Urinates more frequently
- Eats less
- Sleeps more
- Seems quieter
- Has vaginal discharge
As the infection becomes more severe, a dog may develop vomiting, diarrhoea, abdominal pain, dehydration, weakness or collapse.
Symptoms of Pyometra in Cats
Cats can be particularly difficult to assess because they often hide signs of illness.
A cat with pyometra may:
- Become unusually quiet
- Hide more than usual
- Stop eating
- Drink more water
- Urinate more frequently
- Vomit
- Develop diarrhoea
- Have vaginal discharge
- Have a swollen or painful abdomen
- Become weak or dehydrated
Because cats are often discreet when they feel unwell, owners may not realise how sick they are until the disease has progressed.
A sudden change in a cat’s behaviour or appetite should therefore be taken seriously, especially if she is unspayed.
Why Do Dogs and Cats With Pyometra Drink More?
Infection and the body’s inflammatory response can affect kidney function.
These changes may interfere with the kidneys’ ability to concentrate urine. As a result, the animal may produce more urine and become much thirstier.
In dogs, increased thirst and urination can be an important warning sign.
The same changes can occur in cats, although they may be harder to notice.
Owners sometimes assume that increased drinking is caused by hot weather, exercise or diet. A sudden change in thirst should not be ignored, particularly in an intact female.
When Does Pyometra Occur?
Pyometra is associated with hormonal changes during the reproductive cycle.
In Dogs
Pyometra commonly develops during the weeks following heat, when progesterone remains elevated.
The exact timing varies between individuals.
If an intact female dog becomes unwell several weeks after a heat cycle, pyometra should be considered.
Remembering the date of the last heat can provide useful information for your veterinarian.
In Cats
The timing in cats is more closely related to ovulation and the resulting hormonal changes.
Because cats are induced ovulators, the reproductive history can be particularly useful when a veterinarian is investigating suspected pyometra.
A cat that has recently been in heat or has had mating or hormonal stimulation may have reproductive changes that are relevant to the diagnosis.
Can a Dog or Cat With Pyometra Still Seem Normal?
Yes.
This is one of the reasons pyometra can be difficult to recognise early.
Some animals initially show only mild changes.
A dog may simply drink more, eat slightly less or sleep more than usual.
A cat may hide more, become quieter or stop interacting with the family.
Other animals become severely ill within a short period.
The outward appearance of a dog or cat does not always reflect the severity of the infection.
For that reason, owners should not wait until their pet looks critically ill before seeking veterinary advice.
How Is Pyometra Diagnosed?
Veterinarians usually combine the animal’s history, physical examination, blood tests and diagnostic imaging.
1. Medical History
Your veterinarian may ask:
- Is the female spayed?
- When was her last heat?
- Has she had puppies or kittens?
- Has she mated?
- Has she received hormonal medication?
- When did the symptoms begin?
- Has her drinking changed?
- Has her urination changed?
- Has her appetite changed?
The answers can provide important clues.
2. Physical Examination
The veterinarian will assess the animal’s overall condition.
They may look for:
- Dehydration
- Abdominal pain
- Abdominal enlargement
- Weakness
- Fever
- Vaginal discharge
- Signs of systemic illness
Cats may require particularly careful examination because they can hide signs of illness.
3. Blood Tests
Bloodwork can provide information about inflammation, infection, hydration and organ function.
Some animals develop significant changes in their white blood cell count.
Severe disease can also affect kidney function, electrolytes and other organ systems.
Blood results can vary, however. A less dramatic result does not necessarily exclude pyometra.
Blood tests are also important for assessing the patient’s condition before anaesthesia and surgery.
4. Ultrasound
Abdominal ultrasound is one of the most useful diagnostic tools for suspected pyometra.
It can show an enlarged uterus containing fluid and can provide information about the uterine wall and its contents.
Importantly, ultrasound can help identify pyometra when there is no visible vaginal discharge.
5. X-Rays
Abdominal radiographs can also help identify an enlarged uterus.
Ultrasound usually provides more information about the uterine contents, so your veterinarian may recommend one imaging method or both depending on the individual patient.
Is Pyometra an Emergency?
Yes. Pyometra should be treated as a veterinary emergency in both dogs and cats.
The disease can progress from relatively mild symptoms to severe systemic illness.
Potential complications include:
- Severe dehydration
- Sepsis
- Endotoxaemia
- Kidney dysfunction
- Organ dysfunction
- Low blood pressure
- Shock
- Uterine rupture
- Peritonitis
Closed pyometra can be especially concerning because infected material cannot drain through the cervix.
If an intact female dog or cat develops symptoms that could indicate pyometra, contact a veterinarian promptly.
Do not wait several days to see whether the symptoms disappear.
How Is Pyometra Treated?
For most dogs and cats, surgery is the treatment of choice.
The usual procedure is an ovariohysterectomy. During surgery, the veterinarian removes the infected uterus and ovaries.
However, pyometra surgery is not the same as a routine elective spay.
A sick patient may already be dehydrated or affected by sepsis, low blood pressure, kidney dysfunction or other complications.
Stabilisation Before Surgery
Depending on the patient’s condition, treatment may include:
- Intravenous fluids
- Appropriate antimicrobial therapy
- Pain relief
- Electrolyte correction
- Cardiovascular support
- Treatment for shock
- Monitoring of kidney function
- Other supportive care
The veterinary team will stabilise the patient as much as reasonably possible before anaesthesia.
Once the animal is ready for surgery, removing the infected uterus eliminates the primary source of infection.
The exact treatment plan depends on the patient’s condition and severity of disease.
What Happens During Pyometra Surgery?
During surgery, the veterinarian removes the infected reproductive tract.
The procedure can be more challenging than a routine spay because the uterus may be enlarged, fragile and filled with infected material.
Careful handling is therefore essential.
The surgical team also takes precautions to reduce the risk of infected material leaking into the abdominal cavity.
The patient’s condition before surgery plays an important role in the overall risk.
A dog or cat diagnosed early may be relatively stable. Another patient may already have severe sepsis, shock or organ dysfunction.
Early diagnosis can therefore make a significant difference.
Can Pyometra Be Treated Without Surgery?
Sometimes, but medical treatment is only appropriate for carefully selected patients.
Veterinarians may consider medical treatment in certain breeding animals when preserving fertility is particularly important.
Treatment can involve medications that counteract progesterone and encourage the uterus to open and empty. Antimicrobial and supportive treatment may also be required.
This approach is not suitable for every patient.
A severely ill animal is generally a poor candidate for medical management. Closed pyometra also presents particular concerns because infected material cannot drain normally.
Another important consideration is recurrence.
Even after successful medical treatment, pyometra can return during a future reproductive cycle.
For most pet dogs and cats that are not intended for breeding, surgery remains the preferred and most definitive treatment.
Can Pyometra Be Prevented?
Yes.
The most reliable way to prevent conventional pyometra is to remove the source of the hormonal reproductive cycle.
This can be achieved through procedures such as:
- Ovariectomy
- Ovariohysterectomy
The ideal timing and surgical approach should be discussed with your veterinarian.
Factors such as species, breed, size, age, health and future breeding plans may influence the decision.
For a female dog or cat that is not intended for breeding, discussing sterilisation with your veterinarian is one of the most effective ways to prevent pyometra.
Can a Spayed Dog or Cat Get Pyometra?
A correctly performed ovariohysterectomy removes both the ovaries and uterus. Conventional pyometra cannot develop when there is no uterus remaining.
An ovariectomy removes the ovaries while leaving the uterus in place. Removing all functional ovarian tissue eliminates the hormonal cycling associated with conventional pyometra.
What Is Stump Pyometra?
Stump pyometra can occur when uterine tissue remains and functional ovarian tissue is also present.
An ovarian remnant is one possible cause.
Remaining uterine tissue can respond to ovarian hormones. Under these circumstances, infection can develop.
A previously spayed dog or cat that develops signs suggestive of pyometra should therefore still be examined by a veterinarian.
Can Hormonal Medications Increase the Risk?
Some hormonal medications can affect the reproductive tract and may increase the risk of uterine disease.
Owners should therefore never use hormonal medication to control heat cycles without veterinary guidance.
Tell your veterinarian about any hormonal medication your pet has received.
This information can be important when assessing reproductive problems.
Pyometra in Dogs vs. Cats: What Is Different?
Dogs and cats can both develop pyometra, and many clinical signs are similar.
However, there are several important differences.
| Feature | Dogs | Cats |
|---|---|---|
| Pyometra risk | Relatively common in intact females | Less common, but potentially serious |
| Reproductive cycle | Ovulation occurs as part of the cycle | Ovulation is usually triggered by mating or hormonal stimulation |
| Typical warning signs | Increased thirst, urination, lethargy, reduced appetite and discharge | Reduced appetite, hiding, lethargy, increased thirst and sometimes discharge |
| Visible discharge | More easily noticed in open pyometra | May be missed because cats often groom themselves |
| Closed pyometra | Can occur | Can occur |
| No discharge | Does not rule out disease | Does not rule out disease |
| Diagnosis | History, examination, bloodwork and imaging | History, examination, bloodwork and imaging |
| Treatment | Surgery is generally definitive | Surgery is generally definitive |
| Prevention | Spaying prevents conventional pyometra | Spaying prevents conventional pyometra |
One of the most important differences for owners is how illness may appear at home.
Dogs may show obvious changes in thirst and urination, while cats may simply hide, stop eating or become unusually quiet.
Neither species should be considered safe simply because the symptoms initially appear mild.
7 Things Every Owner of an Unspayed Female Dog or Cat Should Know
1. Pyometra can occur at a relatively young age
Older animals have a higher risk, but young dogs and cats can also develop the disease.
2. Your pet does not need to have had babies
Having puppies or kittens does not protect a female from pyometra.
3. Vaginal discharge may be absent
Open pyometra may produce discharge, but closed pyometra may produce none.
Cats may also groom away visible discharge.
4. Increased thirst can be an important warning sign
A sudden increase in drinking or urination deserves attention.
5. Your pet may initially look relatively well
Some animals show only subtle changes before becoming seriously ill.
6. Pyometra can become life-threatening
Sepsis, organ dysfunction, shock and uterine rupture are possible complications.
7. Early veterinary care matters
Prompt diagnosis allows the veterinary team to begin stabilisation and treatment before severe complications develop.
Frequently Asked Questions About Pyometra
Is pyometra contagious?
No. Pyometra is not considered a contagious disease that spreads between dogs or cats.
The condition develops within an individual animal’s reproductive tract.
Can a dog get pyometra after one heat cycle?
Yes. The risk generally increases with age and repeated reproductive cycles, but pyometra can develop after relatively few cycles.
Can a cat get pyometra after one heat?
A cat can develop pyometra even without a long history of reproductive cycles. The risk is related to hormonal changes and bacterial infection rather than simply the number of times a cat has been in heat.
Can a young dog or cat get pyometra?
Yes. Young age does not completely rule out the disease.
Can a spayed dog get pyometra?
Conventional pyometra cannot occur after a correctly performed procedure that removes all functional ovarian tissue and the uterus when applicable.
However, infection involving remaining uterine tissue can occur if functional ovarian tissue remains.
Can a spayed cat get pyometra?
The same principle applies to cats. A correctly performed sterilisation procedure prevents conventional pyometra.
If ovarian tissue remains, however, hormone-responsive uterine tissue can potentially become infected.
Does pyometra always cause vaginal discharge?
No.
Open pyometra may cause visible discharge, while closed pyometra may produce none.
Cats may also clean away discharge before their owner notices it.
Can antibiotics cure pyometra?
Antibiotics may form an important part of treatment, particularly when infection has spread beyond the uterus.
However, antibiotics alone generally do not remove the infected uterus.
For most patients, surgery provides the definitive treatment.
Is pyometra painful?
It can be.
Some animals develop obvious abdominal pain or discomfort. Others show surprisingly subtle signs during the early stages.
Can pyometra come back after medical treatment?
Yes.
Recurrence is an important concern after medical management, especially when the animal remains intact.
When Should You Contact a Veterinarian?
If you have an unspayed female dog or cat, pay attention to changes in behaviour, appetite, drinking and normal routines.
Contact your veterinarian promptly if you notice:
- Increased drinking
- Increased urination
- Loss of appetite
- Vomiting
- Diarrhoea
- Lethargy
- Abdominal enlargement
- Abdominal discomfort
- Vaginal discharge
- Fever
- Weakness
- Hiding or unusual withdrawal
Severe weakness, collapse, breathing difficulties or a swollen and painful abdomen require urgent emergency veterinary care.
Do not wait for vaginal discharge to appear.
The Most Important Thing to Remember About Pyometra
Pyometra can initially look like a mild illness in both dogs and cats.
An intact female dog may simply drink more water, eat less or seem quieter than usual.
A cat may hide, stop eating or become unusually withdrawn.
The absence of vaginal discharge does not rule out the disease.
Closed pyometra can develop without any external discharge while infection continues to build inside the uterus.
For most affected pets, surgery to remove the infected reproductive tract is the safest and most definitive treatment.
Early recognition and veterinary treatment can make a significant difference.
If your female dog or cat seems unwell, especially following reproductive activity or a recent heat cycle, contact your veterinarian rather than waiting for symptoms to become severe.
Veterinary Perspective
“One of the most important things I would want owners to understand is that pyometra does not always look dramatic at the beginning. A dog or cat may initially drink more, eat less, hide more or simply seem quieter than normal. By the time some patients become obviously sick, the infection can already be affecting the whole body. That is why recognising changes in an unspayed female is so important.”
— Dr. Stylianos, DVM
Medical Disclaimer
This article is intended for general educational purposes and is not a substitute for an examination by a qualified veterinarian.
Pyometra can become life-threatening and should not be diagnosed or treated at home.
If you are concerned that your pet may have pyometra, contact your veterinarian or an emergency veterinary service promptly.
References and Further Reading
- Merck Veterinary Manual — Cystic Endometrial Hyperplasia–Pyometra Complex in Small Animals
- American College of Veterinary Surgeons — Pyometra
- American College of Veterinary Surgeons — Ovariohysterectomy
- Relevant peer-reviewed veterinary literature on canine and feline reproductive disease
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