Pyometra in Dogs

Pyometra in dogs

A secondary infection arising from hormonal changes within an unspayed dog’s reproductive tract, pyometra may be diagnosed in middle-aged, intact female dogs but is more commonly found in older dogs. Pyometra in dogs is a serious infection requiring surgical treatment involving removal of infected ovaries and uterus (ovariohysterectomy or “spay”). Signs of pyometra generally emerge two weeks to two months following the last heat cycle (estrus).

What Causes Pyometra in Unspayed Dogs?

After several years of experiencing uninterrupted estrus cycles that do not result in pregnancy, a female dog’s uterine wall sustains changes promoting the development of pyometra. During a heat cycle, white blood cells meant to prevent infection do not enter the uterus so that sperm can transfer into the dog’s reproductive tract with suffering damage by white blood cells.

After estrus, an intact female dog’s progesterone levels remain higher than normal for up to eight weeks. This causes thickening of the uterine lining in preparation for a possible pregnancy. However, if pregnancies do not occur over several heat cycles, the uterine lining continues to thicken, causing cysts to form inside tissues (cystic endometrial hyperplasia). A thick, cystic-lined uterus releases fluids that encourage bacterial growth and infection. In addition, excessive progesterone inhibits contraction of uterine muscles necessary for expelling bacteria and accumulated fluids in the uterus.

Owners of unspayed female dogs who give their dogs progesterone-based medications for reproductive system conditions should be aware that these drugs can cause uterine lining changes similar to those promoting pyometra. Intact female dogs receiving hormonal drugs should be monitored by a veterinarian.

Do Most Unspayed Dogs Get Pyometra?

The more heat cycles a female dog goes through, the more likely she is to be diagnosed with pyometra. Also, the number of pregnancies a dog has does not increase or decrease her risk for pyometra. Development of the disease is directly associated with the number of estrus cycles causing thickening of the uterine lining.

What are the Symptoms of Pyometra in Dogs?

When the dog’s cervix is open, pus from the infection drains through the uterus and out of the vagina. Owners of dogs with pyometra may notice sticky or dried discharge on the hair and skin under the tail, on bedding and wherever the dog normally lies. Lack of appetite, lethargy, fever, and depression may or may not accompany discharge.

When the cervix is closed, pus cannot drain out through the vagina. Instead, it remains in the uterus where it accumulates and forces distension of the dog’s abdomen. Pyometra bacteria excrete toxins easily absorbed into the bloodstream. Dogs with “closed” pyometra suffer severe symptoms rapidly, becoming anorexic, listless and feverish. They may also vomit and have chronic diarrhea leading to a risk of dehydration and malnutrition.

Bacteria toxins affect the kidneys by increasing urine production. Dogs will drink water excessively if their kidneys have been infiltrated with bacteria. In addition, closed pyometra may cause a rupture of the uterus, allowing pus to seep into the abdomen, cause peritonitis and possibly death if emergency treatment isn’t provided.


Evaluation of symptoms and white blood cell count via a complete blood test are two primary ways a veterinarian will diagnose pyometra. Urine concentration (gravity) is usually low due to bacterial toxins interfering with kidney functioning.

X-rays can show whether the dog’s cervix is open or closed. Radiographs revealing an enlarged uterus indicates a closed cervix. Minimal enlargement of the uterus means the dog likely has an open uterus that allows pus to drain out of the body. Ultrasound examinations are helpful for differentiating quickly between pregnancy and pyometra. In addition, an ultrasound reveals the extent of uterine wall thickening, accumulation of fluid in the uterus and uterine enlargement.


When dogs are diagnosed with pyometra in its early stage, surgical removal of the uterus is an uncomplicated procedure similar to spaying. Since pyometra at its onset does not usually present noticeable symptoms affecting the dog’s health, most cases of pyometra are caught at a later stage when surgery is more complicated. Dogs undergoing surgery for pyometra require hospitalization, intravenous fluids while recovering and antibiotics following surgery to prevent infection.

Dogs are kept on antibiotic therapy (amoxicillin-clavulanate) for one to two weeks. A final blood and culture test is necessary to ensure the infection has been completely eliminated from the dog’s body.

Stabilizing Dogs Before Treatment

Before initiating treatment, veterinarians need to stabilize dogs with pyometra by correcting glucose and electrolyte imbalances and restoring normal tissue perfusion. Antibiotics can help reduce the severity of the bacterial infection so that surgery does not exacerbate the infection. Vets will send bacteria cultures taken from a surgically removed uterus to a laboratory for a definitive diagnosis of pyometra.

Noninvasive Treatment for Pyometra

Nonsurgical treatment for pyometra is available but has a lower success rate and a risk of complications. This treatment using prostaglandins is usually reserved for professional breeders who own unspayed female dogs diagnosed with early-stage pyometra.

Prostaglandins are hormones that reduce progesterone levels to relax cervix muscles so that the cervix opens and expels pus. Side effects of prostaglandins include panting, excessive salivation, vomiting and stomach pain, which last about two or three hours and may be alleviated by walking the dog 30 minutes after the injection is given.

Dog owners should be aware that prostaglandin treatment cannot be used for closed pyometra since the cervix won’t open enough to allow drainage of pus. In addition, dogs given prostaglandins will need to breed on their next estrus cycle to reduce their risk of suffering a recurring bout of pyometra.

Advantages of Ovariohysterectomy for Pyometra Over Prostaglandins

Removing the uterus and ovaries of dogs with pyometra is not only curative but will prevent recurrence of pyometra. However, there are risks to an ovariohysterectomy when the dog has pyometra, such as hypotension, cardiac arrhythmia, and aspiration pneumonia. To prevent fragile uterine walls from tearing during an ovariohysterectomy due to pyometra, veterinarians must make a larger than normal abdominal incision to allow for easier exteriorization and exposure of the dog’s uterus. This is necessary to minimize the risk of rupture within the abdomen and release of infected material.

If Your Dog Needs an Ovariohysterectomy Due to Pyometra

Dog wearing cone after a ovariohysterectomy

Owners will need to withhold food (not water) for at least 12 hours before surgery to prevent nausea and vomiting. Before any type of surgery, dog owners should be aware that their dogs should be current on bordetella (kennel cough), distemper and rabies vaccinations. Veterinarians may also perform a fecal exam and heartworm test prior to surgery to rule out intestinal parasites.

Dogs under anesthesia are constantly monitored during an ovariohysterectomy using veterinary medical devices. Prior to sedation, vets examine a dog’s vitals to ensure the dog is healthy enough to accept the anesthesia. The minimal amount of anesthesia is administered to fully sedate a dog prepped for surgery.

Sutures used to close most surgical incisions are absorbable, meaning they are placed under the skin where your dog’s body chemistry naturally dissolves the sutures. Although many dogs do not even realize they have sutures, some may lick or chew their sutures excessively. If this occurs, you may need to get your pet an Elizabethan collar (cone) to prevent tampering and inadvertent opening of sutures.

Dogs undergoing surgery for pyometra will feel exactly how people feel after any kind of surgery–tired, a little nauseous and in some pain. New pain medications formulated specifically to address post-operative pain in dogs work well to reduce discomfort and help them rest peacefully. NEVER give dogs human aspirin or ibuprofen. Call your vet if you think your dog needs more pain medication and abide by the vet’s instructions regarding pain relievers.

Recovery rates of ovariohysterectomies depend on the dog’s health condition and age prior to surgery. Most dogs suffering pyometra and having an ovariohysterectomy will remain at the vet’s for several days before they are released to their owners.

While recovering, dogs should be allowed outside only to use the bathroom for a few days after surgery. Be aware that some dogs may need to go outside more often than usual since they may have been given fluids during the procedure that makes them urinate frequently. Also, remember to monitor their bathroom habits to ensure they are defecating and urinating normally.

Swelling around the surgical site is expected and usually subsides within several days. However, any oozing or foul odors coming from the incision means that it could be infected and requires the immediate attention of the veterinarian.

Incision Care and Bacterial Infections Like Pyometra

Although antibiotics work well to eliminate bacteria, just a few bacteria left behind following an ovariohysterectomy can cause infection to redevelop, especially in the surgical incision. If a dog’s incision is not healing properly, one or more of the following may be causing the problem:

Antibiotic-Resistant Bacteria Infiltrates the Incision

One of the most prevalent bacteria in the world, Pseudomonas aeruginosa, is found in many chronic wounds and presents a strong resistance to standard antibiotics. Wounds infected by P. aeruginosa may have a bluish tinge to them due to bacteria consuming fluids in the wound and releasing waste. Serious P. aeruginosa infections generally affect only dogs with compromised immune systems.

Foreign Bodies Embedded in the Incision

Owners should make sure their dog’s incision is completely clean before applying appropriate dressings. Various debris or bits of gauze and other dressing materials remaining in the wound will attract bacteria and prevent the wound from healing normally.


Impaired circulation combined with glucose-heavy blood not only delays healing of incisions but also promotes bacterial infection.

Inadequate Nutrition

Your dog’s nutrition also plays a vital role in recovering from pyometra and an ovariohysterectomy. Protein is particularly helpful for promoting new cell and tissue growth. Chicken, fish, turkey, eggs, yogurt, peanut butter and cheese are all excellent sources of protein.

Incisions that will not heal are at risk for developing infections. Incisions that spontaneously bleed, exude odorous drainage and appear to increase in size are probably infected and should be attended to by a veterinarian as soon as possible. Consequences of untreated incision/wound infections include necrosis, cellulitis, and sepsis, all conditions possibly requiring hospitalization.

Are Certain Dog Breeds Prone to Pyometra?

According to studies, certain dog breeds present an increased risk of pyometra. The top 10 breeds more prone to pyometra than other dog breeds are Irish Wolfhounds, Airedale Terriers, Dobermans, Bernese Mountain dogs, Great Danes, Rottweilers, Staffordshire Bull Terriers, Leonbergers, Bull terriers and Bouvier des Flandres dogs.

However, ALL unspayed female dogs of any breed can be diagnosed with pyometra. The best preventative to pyometra is an ovariohysterectomy.

Stump Pyometra

A rare type of pyometra called stump pyometra can occur in dogs that have been spayed but still experience residual functioning of ovary tissues. Stump pyometra happens when a remaining piece of an excised uterus develops an infection and fills with pus. Since symptoms are similar to regular pyometra, diagnosis of this condition is challenging to veterinarians who know the dog has been spayed. Blood tests and imaging scans are required to quickly determine if stump pyometra exists so that treatment can be initiated.

Physical and Psychological Benefits of Spaying

Spaying female dogs can help reduce a variety of unwanted behaviors, such as roaming (searching for unneutered males), restlessness and anxiety attributed to estrus hormones, aggression around competing (unspayed) females, bleeding from the vagina and frequent urination that may result in “accidents”.

Spayed females dogs also experience fewer health issues than unspayed female dogs because of decreased hormones in the bloodstream. Tumors in unspayed dogs may develop due to continued estrogen release. Common tumors affecting intact female dogs include:

Basal cell tumors–usually developing on the neck, shoulders, and head of older dogs, basal cell tumors are round nodules that may ulcerate.

Hemangiomas–composed of new blood vessels that are too tightly clustered together, hemangiomas are commonly seen on the spleen and skin of dogs. They require removal because they can metastasize or bleed profusely if hit or cut.

Mast cell tumors–Developing either subcutaneously or on the skin, mast cell tumors can take on different appearances–smooth bumpy, firm, soft, ulcerated or hairless. You may find a mast cell tumor on your dog’s legs, near his anus or on his trunk. Some dog breeds seem more prone to mast cell tumors, including Labradors, Dachshunds, Beagles, and Boxers.

Papillomas–also called canine warts, viral papillomas arise from ducts, skin and mucous membranes related to glandular tissue. Although they are not painful or harmful to dogs, papillomas often develop in large numbers on young dogs, especially Poodles, Pugs and Cocker Spaniels.

Bladder Infections in Unspayed Dogs

Certain factors may increase the risk of both intact female and male dogs to have bladder infections. Females are more prone to bladder infections due to hormones and pregnancy. Animals with depleted immune systems due to advanced age, chronic illnesses such as diabetes or cancer or severe oral infections are often diagnosed with a bladder infection. Overweight dogs unable to adequately groom and clean their genital area, incontinent pets and pets with untreated bladder stones are at a higher risk of developing bladder infections.

Symptoms of a Bladder Infection in Dogs

Bladder infection symptoms in unspayed dogs somewhat mimic signs of pyometra in its early stages. Symptoms include:

  • Frequent urination (having accidents or urinating in odd places)
  • Straining to urinate (continuing to act like they are urinating when nothing is being eliminated)
  • Traces of blood in urine
  • Strong, foul odor to their urine
  • Vocalizing while urinating (whining may indicate it hurts to urinate)

Dogs with bladder infections may eat very little, appear lethargic and run low-grade fevers as well. Some dogs will have bladder infections without showing any symptoms until the infection is severe.

Differentiating a bladder infection from pyometra involves urine testing and analysis to provide results veterinarians need to detect and begin treating a bladder infection. A painless procedure called a cystocentesis withdraws a urine sample from your dog’s bladder that is then examined for bacterial infection. If an infection is discovered, your vet will prescribe antibiotics appropriate for eliminating the infection. Neglecting to address a bladder infection can cause your dog to experience weight loss, chronic pain and damage to their kidneys and urinary tract.

Endocrine Disorders in Unspayed Dogs

Hormonal imbalances in dogs can detrimentally affect the functioning of an intact dog’s nervous, cardiovascular and reproductive systems. Identifying endocrine problems in dogs as early as possible means a veterinarian can begin treatments necessary for restoring hormonal imbalance and reducing symptoms of several chronic diseases.

Comprised of several glands that release a wide variety of hormones into the bloodstream, your dog’s endocrine system is responsible for regulating her growth, metabolism, maturation and reproductive processes. Hormonal imbalances occur at any age, with most imbalances caused by chronic diseases, autoimmune disorders or infections. Common endocrine disorders diagnosed in unspayed dogs include:

Hyperthyroidism–signs of too much thyroid hormone in the bloodstream include weight loss with increased appetite, hyperactivity, diarrhea, vomiting, and excessive thirst.

Hypothyroidism–signs of too little thyroid hormone in the bloodstream include hair loss, flaky skin, weight gain, sluggishness and recurring ear infections.

Hypercalcemia–signs that a dog has too much-circulating calcium include appetite loss, vomiting, weakness and swelled lymph nodes. Dogs with hypercalcemia will drink more water but also urinate more. This could lead to dehydration although a dog is drinking water frequently.

Hyperparathyroidism–elevated levels of parathyroid hormone can cause stiffness, lethargy, vomiting, urinary incontinence and increased thirst.

Diabetes mellitus–when certain pancreatic cells fail to maintain proper blood glucose levels, unspayed dogs may suffer symptoms of diabetes mellitus, such as increased appetite, thirst, and urination. Weight loss, poor coat and skin condition, and vomiting are other indicators of possible diabetes mellitus in dogs as well.

Imbalance of sex hormones–abnormally low or high levels of testosterone, progesterone or estrogen in dogs may cause hair loss, severe skin irritations, outer ear inflammation and urinary incontinence.

Overactive glands may be treated with medications, radiotherapy or surgery to remove tumors responsible for glandular dysfunction. Abnormal hormone levels may be supplemented with synthetic hormones, such as insulin for diabetes mellitus. Thyroid hormone replacements can be given orally to dog with hypothyroidism. When dogs are diagnosed with a hormonal imbalance, they will require periodic blood tests to ensure they are receiving the correct medication dosage.


Pyometra is a serious infection caused by repeated heat cycles in dogs that thicken uterine wall linings and prevent white blood cells from entering the uterus. Treatment for dogs diagnosed with pyometra includes ovariohysterectomy (removal of the uterus and ovaries) or injections of prostaglandins. The best way dog owners can prevent their female dogs from suffering pyometra is to get them spayed as soon as possible, preferably before a female dog experiences her first estrus cycle.

Pyometra treated dog laying on grass