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Pyometra in Dogs

**Warning** : this article about pyometra in dogs contains graphic images of internal canine anatomy and may not be suitable for all audiences. Reader discretion is advised.

If you are a dog owner, chances are that you may have heard of pyometra. Reproductive issues are particularly common among modern dogs and sadly, pyometra is one of the most frequently diagnosed issues in intact female dogs.

Pyometra in dogs

What is Pyometra in Dogs?

Canine pyometra is a common, potentially life threatening, bacterial infection of a dog’s uterus. This results in accumulation of pus in the uterus of sexually intact bitches, typically occurring between 4 weeks and 4 months after a heat cycle.

There are two types – open and closed. To understand the difference, a basic understanding of dog reproductive system and it’s anatomy is needed.

Canine uterus anatomy

Canine uterus anatomy
Joel Mills, CC BY-SA 3.0 , via Wikimedia Commons

The female dog’s reproductive system consists of vulva, vagina, cervix, two oviducts, uterus and two ovaries. The characteristic Y-shaped uterus has three well-differentiated anatomic parts – neck, body and two horns. The uterus ends with the cervix (which serves like a barrier between the uterus and the external environment). It’s the status of this cervix that is primary importance in this disease.

Open vs closed pyometra

Based on the patency of the cervix, pyometras can be categorized as either open or closed. As the name itself suggests, in open pyometras, the cervix is open thus allowing drainage of the accumulated pus.

On the flip side, in closed pyometras, the cervix is closed and the pus has nowhere to go. Consequently, the pus keeps accumulating which at first leads to uterine enlargement and abdominal distension. As time passes, the toxins from the accumulated pus may enter the bloodstream leading to shock and septicaemia (poisoning of the blood).

Stump pyometra

Stump pyometra is a condition occurring in inappropriately spayed females. Namely, if there is a small ovarian tissue left behind at the time of desexing, that small portion continues to retain its hormonal activity. The hormones can eventually affect the remaining uterine tissue causing a so-called true stump pyometra.

Pyometra vs metritis

Both pyometra and metritis are womb infections. The difference is, in cases of metritis, the infection is caused by bacteria that do not produce pus. Usually, bitches with metritis show no clinical signs but when used for subsequent breeding, fail to conceive.

How Do Dogs Get Pyometra?

The pyometra is a hormonally mediated, two-phased, pathological process. The first pathological change is cystic endometrial hyperplasia (CEH) or thickening of the uterine lining due to repeated heat cycles. High oestrogen levels followed by prolonged and high progesterone levels, promote endometrial hyper-reactivity and gradual cystic hyperplasia.

The second pathologic change is infection. The cervix, as a gateway to the uterus, remains tightly closed, at all times, except during oestrus, when it relaxes, in order to allow the sperm to enter the uterus. If the cervix is not closed, vaginal bacteria may easily enter the uterus.

Normally, the uterine environment does not support bacterial growth and survival. However, the pathologically changed uterine lining, as outlined above, creates perfect conditions for bacterial residence. Additionally the progesterone influenced and thickened wall prevents the uterine muscles from properly contracting. Therefore the bacteria that entered the uterus cannot be expelled and cleared.

Is it hereditary?

The fact that certain dog breeds are more likely to develop pyometra while still young suggests the condition may have genetic predisposition. However, this theory is still undergoing intense research.

Breeds reported to be predisposed to pyometra include:

  • Irish Terriers
  • Chow Chows
  • Bernese Mountain Dogs
  • Rottweilers
  • Rough-haired Collies
  • Cavalier King Charles Spaniels
  • Golden Retrievers

On the other hand, breeds with low risk for pyometra include:

  • German Shepherds
  • Dachshunds
  • Swedish Hounds

How common is pyometra in dogs?

Pyometra is perhaps the most common life-threatening reproductive condition in intact females. According to statistics, 1 in 4 non-spayed female dogs will develop the condition before reaching the age of ten years. In other words, pyometra occurs in approximately 25% of intact female dogs.

Which dogs are affected most frequently?

Pyometra usually occurs in older females (>6 years) as a result of repeated exposure to heat hormones (such as oestrogen and progesterone). Abnormal heat cycles, fake pregnancies and hormonal treatments (e.g mismating injections) increase the risk of this disease.

Clinical Signs of Pyometra in Female Dogs

The main problem with pyometra is that the onset of clinical signs is gradual, insidious and often misunderstood. The type of the clinical signs and their intensity also depends on the patency of the cervix.

Dog drinking excessively
Drinking excessively is a classic symptom

In cases of open pyometra, there will be visible discharge draining from the dog’s vulva. Discharge can often be seen on the skin or hair under the tail, as well as on the dog’s bedding. Affected dogs can be either febrile or hypothermic, with reduced or absent appetites, usually increased water intake and increased urination frequency. Varying degrees of lethargy and depression will also usually be present.

In cases of closed pyometra, the discharge accumulates in the uterus with no where to go, ultimately causing abdominal distension. Because the bacterial toxins eventually enter the bloodstream, dogs become ill very rapidly. The systemic signs of the condition are same as with open cervix pyometra, but usually much more severe.

Discharge colour

In open pyometra, the vaginal discharge is thick and odoriferous and its colour varies from yellow-green to pinkish-red. The exact colour depends on whether it contains only pus or if there is blood or mucus as well.

Pyometra discharge colour
Dark red purulent pyometra discharge


An experienced vet can usually diagnose open pyometra from the symptoms alone. In the early stages, with little or no discharge, a blood test will usually indicate the presence of infection in the body.

Radiology and ultrasound

Diagnosis of closed pyometra is confirmed by x-ray or ultrasound, both of which will show an enlarged uterus (the enlargement is often described as sausage-like). The uterus can enlarge to an abnormal size, even larger than it does for a full litter of pups. Both of these diagnostic imaging procedures may be used to distinguish between pyometra and pregnancy.

Pyometra radiology
Pyometra radiology. Kalumet, CC BY-SA 3.0 , via Wikimedia Commons
Pyometra ultrasound pictures
Ultrasound representation of pyometra in a dog. 30.8.2004, Author: Kalumet.

Canine Pyometra Treatment

Pyometra is considered a serious and life threatening, medical emergency that requires rapid and aggressive intervention. Without treatment, the infection is fatal. Generally speaking, there are two approaches to treatment – medical and surgical.

Medical treatment

The medical approach includes potent antibiotics and a hormone called prostaglandin 2-alpha. Medical treatment is considered only for bitches of extreme breeding value with open pyometra and mild clinical signs.

Sadly, medical management does not guarantee a positive outcome. In medically managed patients, the recurrence rate is particularly high and there is usually a decreased future breeding capacity (50% chance of successful subsequent breeding).

Pyometra surgery in dogs

The treatment of choice, for both closed and open pyometra is immediate surgical ovariohysterectomy (complete removal of the ovaries, oviducts and uterus) or spaying. In timely managed situations, the success rate of the surgical management is 100%.

The main advantage of surgical over medical management is that it is both curative and preventative.

Pyometra surgery in dogs
Pyometra weighing 4.5kg. Photo courtesy Ritu Sood - Australian Veterinary Network

How much does surgery cost?

A pyometra surgery usually costs between $1000 and $2000. This is because the surgery is more challenging than routine spays (the distended uterus is brittle, friable and easily breakable which may lead to spilling its toxic contents into the otherwise sterile abdomen) and require special handling. Intensive aftercare is often also required, particularly if pets present initially in a very poor state with systemic sepsis.

What to expect after surgery?

Most dogs recover tremendously within several days after surgery. After being discharged from the hospital, the patients will need to continue receiving its prescribed antibiotic for approximately 1-2 weeks. Regular follow-ups with your veterinarian are recommended.

Pyometra Survival Rate

Unfortunately, pyometra is a very common and delicate condition and despite modern treatment options, the mortality rate due to pyometra is about 4%. Without treatment the infection is lethal in all cases.

If your pet has recently been on heat and now appears unwell, drinking more than usual, bloated in the abdomen or has a vaginal discharge, be sure to contact your vet immediately. When it comes to the success of dealing with this disease, prompt medical attention is vital to a positive outcome.


Most frequent questions and answers about pyometra in dogs.

The associated vaginal discharge has a particularly repellent, foul smell.

No. Antibiotics can reduce the infection and improve the patient’s overall health status thus making the surgical management safer and simpler. However, they cannot cure the condition.

In most cases pyometra occurs 4 to 8 weeks after heat. However, it can develop much earlier, either immediately after ovulating or as late as four months after ovulating.

Yes, but only if inappropriately spayed (if the ovaries are not fully removed and small ovarian tissue is left behind). Properly spayed dogs cannot develop the condition.

Yes. Under extremely rare circumstances it is possible to have pyometra in one uterine horn and vial foetuses in the other. With proper management, it is even possible to have successful pregnancy.

Yes. Theoretically speaking, an open pyometra can become closed at any time. However, there are very few clinical reports supporting this transformation.

No. As a secondary infection (due to hormonal changes) pyometra is not contagious. Usually it is caused by E. coli bacteria originating from the affected dog’s normal microflora.

No. Today, the term stump pyometra is frequently yet mistakenly used for another condition – stump granuloma. Stump granuloma is focal inflammation of the residual uterine tissue due to a reaction to suture material that has been used. The inflammation may or may not be followed by bacterial infection.

Simple: make sure your dog is spayed. If she is not, watch out for the signs – vaginal discharge (when the pyometra is open) or lethargy, increased thirst and decreased appetite (when the pyometra is closed).

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