Pyometra is a serious infection of the uterus in unspayed female dogs. It usually develops 4 to 6 weeks after a heat, but it can appear anywhere from 2 to 16 weeks later.1,2 It's most common in middle-aged and older dogs, and signs include drinking and urinating more, lethargy, poor appetite, vomiting and either a pus-like discharge from the vulva or a swollen belly.3,2 Pyometra is an emergency. Without prompt treatment, it can lead to shock and death.2,1 Most dogs are treated with emergency spay surgery, and spaying almost always prevents it.3,4,5
Go to a vet now if your unspayed female has, especially within a few months of a heat:
What the Research and Guidelines Say
- It's common. Swedish insurance data on over 260,000 dogs found pyometra in 19% of unspayed females by age 10, and other Swedish research puts it at about 25%.7,8 Those figures come from Sweden, where only about 7% to 10% of dogs were spayed or neutered at the time.9
- Breed matters a lot. By age 10, 66% of Bernese Mountain Dogs, 62% of Great Danes and 58% of Rottweilers in that study had developed it.7
- Most dogs survive with surgery. In a UK study of 1,040 cases, 3.3% of dogs treated surgically died, compared with 12.6% of those treated with medicine alone.10
- Closed pyometra is more severe. In one study, 77% of dogs with a closed cervix had sepsis, compared with 51% with an open cervix.6
What Causes Pyometra?
After each heat, the hormone progesterone thickens the lining of the uterus for a possible pregnancy. Over repeated cycles, the lining can become cystic and prone to infection, usually by bacteria from the vagina such as E. coli.3 That's why pyometra is more common in older females, though it can affect young dogs too.1,11 Hormone treatments, including some used to prevent pregnancy after an accidental mating, also raise the risk.2,11,1
Open vs Closed Pyometra
- Open pyometra: the cervix is open, so pus drains out as a discharge, often with blood. You may notice her licking more or staining on her bedding.1,2
- Closed pyometra: the cervix is closed, so the pus builds up inside. There's no discharge, but her belly may swell, and she can become very ill quickly.1,2
Diagnosis
Your vet will ask when her last heat was, examine her and run blood tests, which usually show a very high white blood cell count.1 An abdominal ultrasound is the best test. It shows an enlarged, fluid-filled uterus and can tell pyometra apart from pregnancy.11,1 Conditions that can look similar include pregnancy, normal heat, fluid or mucus in the uterus without infection, vaginitis and tumors.11
Treatment
- Emergency spay surgery to remove the infected uterus and ovaries is the preferred treatment, after stabilizing her with IV fluids and antibiotics.3,1
- Medical treatment with hormone-type drugs and antibiotics is sometimes used for young breeding dogs that aren't very ill. It's less reliable, it's riskier with closed pyometra because the uterus can rupture, and pyometra often comes back.3,1,2
In a large Swedish hospital study, 1% of dogs died after surgery and 10% died overall, mostly dogs put to sleep without treatment.8 In UK primary care, dogs aged 10 or older had about 20 times the odds of dying from pyometra as dogs under 6, and about 1 in 7 dogs with pyometra were put to sleep within days without treatment. The authors suggested cost or worries about the outlook may explain the higher deaths in older dogs.10 Acting quickly matters.
Can Spayed Dogs Get Pyometra?
Rarely. "Stump pyometra" can occur if a small piece of uterus was left behind after spaying and she still gets progesterone, from leftover ovarian tissue or from hormone treatment. Signs include a bad-smelling discharge, fever and lethargy. It's treated with surgery and antibiotics.5 Any discharge in a spayed dog is worth a vet visit.12
Prevention
Spaying removes the uterus and prevents pyometra.4,13 If you plan to breed your dog, know the signs and watch her closely for about 4 months after every heat.1,14,15 See spaying dogs, dog in heat and swollen vulva and discharge.
Frequently Asked Questions
How do I tell if my dog has pyometra?
Watch for thirst, lethargy, poor appetite, vomiting and a discharge or swollen belly in the weeks after a heat. See a vet urgently.
How long can a dog live with pyometra?
Don't wait. Pyometra can become life-threatening within days, especially if it's closed.
What causes white discharge in a female dog?
Vaginitis is common, but a cloudy or pus-like discharge after a heat can be pyometra. See your vet.
At what age do dogs get pyometra?
On average, dogs are about 7 to 9 years old when it's found, but it can happen at any age after the first heat.
Is pyometra surgery expensive?
It costs more than a routine spay because it's an emergency, often with hospital care.
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Sources and further reading
This article was written and fact-checked on October 22, 2026 against current veterinary references and specialist guidelines:
- Barnes C, Weir M, Ward E. Pyometra in Dogs. VCA Animal Hospitals, updated May 2026.
- Memon MA. Reproductive Disorders of Female Dogs. Merck Veterinary Manual (pet owner version), reviewed June 2018, updated September 2024.
- Scully CM. Cystic Endometrial Hyperplasia-Pyometra Complex in Small Animals. Merck Veterinary Manual, reviewed July 2023, updated July 2026.
- American College of Veterinary Surgeons. Spay. ACVS, updated June 2023.
- Gardiner J. Stump Pyometra. UC Davis School of Veterinary Medicine, April 2019, updated November 2022.
- Jitpean S, Ambrosen A, Emanuelson U, Hagman R. Closed cervix is associated with more severe illness in dogs with pyometra. BMC Veterinary Research 2017;13:11 (SLU summary).
- Jitpean S, Hagman R, Ström Holst B, et al. Breed variations in the occurrence of pyometra and mammary tumours in Swedish dogs. ISCFR/EVSSAR Symposium (IVIS), July 2012.
- Jitpean S, Ström-Holst B, Emanuelson U, et al. Outcome of pyometra in female dogs and predictors of peritonitis and prolonged postoperative hospitalization in surgically treated cases. BMC Veterinary Research 2014;10:6.
- Hagman R. Clinical and Molecular Characteristics of Pyometra in Dogs. ISCFR/EVSSAR Symposium (IVIS), 2012.
- Park KYJ, Reid A, Brodbelt DC, Church DB, O'Neill DG. Clinical outcomes of pyometra in bitches under UK primary veterinary care. Royal Veterinary College VetCompass, ACV Conference 2023.
- Dennis J, Hamm BL. Canine pyometra: Early recognition and diagnosis. dvm360, May 2012.
- Eldredge DM. Why Is My Dog's Vulva Swollen? Whole Dog Journal, January 2025.
- British Veterinary Association, British Small Animal Veterinary Association. BVA and BSAVA policy position on neutering of cats and dogs. BVA, December 2025.
- Hagman R. Pyometra in Small Animals 3.0. Veterinary Clinics of North America: Small Animal Practice 2023;53(5):1223-1254.
- Johnstone G. Everything You Need to Know About Dogs in Heat. American Kennel Club, updated August 2026.
About this article
Last updated : new page, written using the Merck Veterinary Manual, VCA, UC Davis, dvm360 and Swedish and UK research on more than 260,000 dogs, plus International Veterinary Information Service (IVIS) proceedings and recent research.
This page is for general information and is not a substitute for an exam by your veterinarian.
