Pyometra

Pyometra is a potentially life-threatening infection of the uterus. It develops when bacteria (typically E. coli) colonise a uterus that has been primed by progesterone during the luteal phase of the cycle. Progesterone causes uterine changes - glandular proliferation, reduced immune response in the uterus - that create an ideal environment for bacterial growth.

Pyometra almost exclusively affects unspayed females, most commonly in middle age (5–9 years), typically within 8–10 weeks of a season. Every subsequent season slightly increases lifetime risk.

There are two forms:

• Open pyometra: The cervix remains open; purulent (pus-containing) discharge drains from the vulva. Often more visible to owners.
• Closed pyometra: The cervix is closed; pus accumulates in the uterus without external drainage. Signs are more severe and deterioration is faster.

Signs to watch for

The classic presentation occurs 2–8 weeks after a season. Signs include:

Open pyometra:

• Purulent (yellow-green, brown, or bloody) vaginal discharge - often the most obvious sign
• Increased licking of the vulva
• Lethargy and reduced appetite
• Increased thirst and urination (toxins from the infection affect the kidneys)
• Possible mild abdominal distension

Closed pyometra:

• All systemic signs above but NO visible discharge
• Abdominal distension is more pronounced
• Rapid deterioration - vomiting, collapse, fever or low temperature (late stage)
• This form is more dangerous because the diagnosis can be missed and the uterus can rupture

Any entire female dog that is lethargic, off food, drinking more than usual, or generally unwell within two months of a season should be assessed for pyometra - this applies whether or not there is visible discharge.

Immediate action

If you suspect pyometra in an entire female:

• This is an urgent same-day vet appointment at minimum
• If the dog is significantly unwell (vomiting, lethargic, unable to stand, severe abdominal pain), this is an emergency - go without delay

Do not wait for symptoms to improve - pyometra worsens rapidly without treatment.

Treatment

Surgical ovariohysterectomy (spay) - removal of the ovaries, uterus, and fallopian tubes - is the definitive treatment. It resolves the infection and prevents recurrence. In a otherwise healthy dog, outcomes are excellent with prompt surgery.

In unstable patients, IV fluid stabilisation before anaesthesia significantly improves outcomes.

Medical management with aglepristone (a progesterone receptor blocker) and antibiotics is an option in some younger dogs where future breeding is planned. It has a significant recurrence rate and is not suitable for closed pyometra, severely ill dogs, or dogs with an established breeding record that isn't being used. It requires close monitoring and follow-up imaging.

Post-surgical monitoring

Log daily during recovery:

• Appetite and water intake
• Activity level
• Incision site: swelling, discharge, redness, or the dog interfering with the wound
• Temperature if you can take it

Most dogs feel significantly better within 24–48 hours of surgery once the source of infection is removed.

Prevention

Neutering (ovariohysterectomy or ovariectomy) completely eliminates the risk of pyometra. For female dogs not intended for breeding, neutering before or after the first season is the most effective preventive measure.

Timing consideration: In the UK, the current guidance on neutering timing (particularly for large and giant breeds) balances pyometra risk against potential impacts on bone development and joint health. Discuss the appropriate timing for your dog's breed with your vet.

When to contact your vet

Go to the emergency vet immediately if:

• An entire female is showing signs of shock, collapse, severe abdominal pain, or can't stand
• Suspected closed pyometra in a rapidly deteriorating dog

Contact your vet urgently (same day) if:

• Purulent vaginal discharge in an entire female
• Any entire female who is unwell within two months of a season

Frequently Asked Questions

My dog had a season last month and now seems off - could it be pyometra? Yes, it could be. The timing is exactly right. Contact your vet today for assessment. Don't wait to see if it improves.

My dog has an open pyometra and seems quite well - is surgery really necessary? Yes. Open pyometra that appears mild can deteriorate rapidly. Medical management is an option in specific circumstances, but for most intact females, ovariohysterectomy is the safest and definitive treatment. An apparently "mild" case can progress to sepsis and uterine rupture without warning.

My dog is 11 - is she too old for surgery? Age alone is not a contraindication to surgery. Older dogs can tolerate anaesthesia well when managed carefully. The risk of the surgery must be weighed against the certainty of the pyometra progressing without it. Most 11-year-old dogs in otherwise reasonable health are good surgical candidates.

Can pseudopregnancy turn into pyometra? Pseudopregnancy (false pregnancy) occurs in the same luteal phase that predisposes to pyometra. The two conditions can coexist, but pseudopregnancy itself does not turn into pyometra. However, a dog showing pseudopregnancy signs who develops the systemic signs described above should be assessed for concurrent pyometra.

Is pyometra common? Yes - it is estimated that approximately 25% of intact female dogs develop pyometra before age ten. It is one of the most common reasons for emergency surgery in intact female dogs in the UK.