Endometritis and metritis in dogs – symptoms and treatment

Overview

The lining, uterine wall and pyometra

A dog's uterus has two horns: the long uterine horns join a short uterine body. The cervix connects the uterus to the vagina.

The endometrium is the lining of the uterus. Endometritis describes inflammation primarily confined to this lining. In metritis, inflammation involves the uterine muscle layer as well as the lining. In pyometra, the uterus is infected and contains pus. This must be distinguished from other forms of uterine inflammation.

In a biopsy series of 399 females investigated for fertility problems, endometritis was found in 170, or 42.6%. This figure concerns a selected group with fertility problems, rather than the risk for all female dogs. Mild inflammatory cell findings can also occur with normal fertility. Their significance is therefore assessed alongside signs, cycle stage and reproductive outcomes.

Causes

Mating-related and other endometritis

Bacteria and cellular debris can enter the uterus with sperm and seminal fluid during mating. A normal, temporary inflammatory response helps clear them. Uterine contractions and the immune system help empty the uterus. If clearance is delayed, inflammation can persist and reduce fertility.

However, bacteria do not cause every case of inflammation. Bacteria can ascend from the vagina through the cervix, particularly when it relaxes during the cycle.

Accumulation of immune cells called eosinophils in the lining has been associated with foetal loss during the same cycle. Whether this inflammation causes foetal loss or develops as a consequence remains unclear.

Bacteria can also reach the uterus through the bloodstream from elsewhere in the body.

Causes of metritis after birth

Manipulation of the uterus during birth can predispose to bacterial infection. A retained foetus or placental tissue can also underlie inflammation. Dead tissue in the uterus is another possible predisposing factor. A gradually developing fertility problem and a mother becoming acutely ill after birth are therefore assessed from different starting points.

Risk factors

Cystic endometrial hyperplasia, or excessive cystic growth of the lining, predisposes to persistent inflammation associated with mating. During the progesterone-dominant cycle stage, the lining is more susceptible to inflammation. Secretions from uterine glands can then support microbial growth.

After oestrus, uterine contractions are limited or almost absent.

The biopsy study of 399 females found no significant difference in the frequency of endometrial changes between age groups. This does not mean every age group has the same risk for all uterine diseases. In metritis after birth, possible retained tissue and manipulation during delivery are considered instead.

Typical symptoms

The most common finding in subclinical endometritis may be reproductive failure in an otherwise apparently healthy female. Possible observations include:

• Failure to become pregnant despite mating.
• Small litters.
• An established pregnancy ending in embryo resorption or foetal loss.
• Abnormal vaginal discharge.
• Being quieter than usual.

Investigation is also warranted if a litter contains many stillborn puppies or puppies failing to thrive after birth.

Acute metritis after birth often causes clearer signs: fever, loss of appetite, vomiting and weakness. Milk production may decrease or stop. The mother's interest in caring for her puppies may also decline.

Complications and consequences

Conception, embryo development and systemic infection

Inflammation of the lining can impair sperm transport and survival in the uterus. It can also hinder embryo passage. Implantation of an embryo in the uterine lining may be disrupted. If inflammation continues once pregnancy has begun, placental function may be impaired.

Persistent changes can involve scarring of the lining. Uterine glands may also atrophy. In the biopsy series of 399 females, scarring was found in 101, or 25.3%. This finding concerns females investigated for fertility problems and does not mean every case of endometritis causes scarring.

Severe acute metritis can involve sepsis and dehydration. Values reflecting kidney and liver function may also change. Stabilising the mother's general condition then takes immediate priority over planning future breeding.

Diagnosis at the vet

History and ultrasound

Investigation covers intervals between seasons, mating dates, previous litters and any pregnancy losses. Semen quality and monitoring of mating timing are also reviewed. An otherwise normal female is not diagnosed solely because one breeding attempt failed, as reproductive problems have several possible causes.

Ultrasound assesses the lining's thickness, structure and cysts, and fluid in the uterine cavity. However, imaging cannot identify the fluid type with certainty. A little fluid before mating can be physiological without affecting fertility. In a female with previous conception problems, uterine clearance can be assessed by ultrasound 5–14 days after mating.

Sampling the right site

Vaginal culture does not reliably show what is happening in the uterus. Bacteria can normally occur in the vagina at different cycle stages. A uterine sample for culture is preferably taken before antibiotic treatment. A positive culture is interpreted alongside inflammatory cells and clinical findings.

Cells or tissue from the lining can be sampled through the cervix with endoscopic guidance. A uterine lavage sample is an alternative, but its sensitivity and accuracy may be lower than those of a tissue sample. Sampling carries a risk of worsening uterine inflammation or causing pyometra. This is considered particularly for sampling through the cervix during the progesterone-dominant stage.

Interpreting a biopsy

The pathologist is told the cycle stage when a tissue sample is submitted, as uterine structure changes accordingly. Interpretation requires experience with normal and diseased endometrium in female dogs. Of the 170 endometritis cases in the 399-female biopsy series, 52.4% were chronic. A mixed inflammatory response was found in 30.0% of these cases. Acute changes accounted for 17.6%.

The chronic form can involve lymphocytes and plasma cells. Acute changes may show neutrophils or eosinophils, for example. There is no established grading system for biopsy findings from which future fertility can be calculated directly. A normal blood count, meanwhile, does not rule out subclinical endometritis.

Endoscopy and investigation limits

Biopsies can be collected from different uterine sites to detect local changes. In one older study evaluating sampling through the cervix, 31% of samples were suitable for diagnosis. Small samples and crush damage can make a biopsy harder to interpret. Uterine endoscopy is performed under general anaesthesia because sudden movement can increase the risk of uterine perforation. Endoscopy can help target a biopsy to a local change seen on ultrasound. Detailed uterine ultrasound may be harder in a large dog because of the deep abdominal cavity and intervening tissues.

Assessing discharge after birth

Estimates for normal postpartum discharge duration are 3 weeks or 4–6 weeks. Other causes of prolonged discharge include delayed recovery of placental sites and injury to the birth canal or uterus. With subinvolution of placental sites, the mother typically has no signs of systemic illness. Acute metritis is also investigated using discharge cytology and bacterial culture. In systemic illness, blood counts, blood biochemistry, urine and imaging findings are investigated as needed.

Treatment

Targeted treatment

Your vet plans treatment according to the inflammation type, uterine contents and the female's general condition. An antibiotic for bacterial infection is selected using culture and susceptibility testing. Antibiotics are not automatically used for every finding of inflammatory cells in the lining. Unnecessary use can favour the development of resistant bacteria.

In some forms of mating-related inflammation, an NSAID may be considered under a veterinary plan. Timing matters, as treatment given too early can impair ovulation. Medicines regulating uterine activity can support clearance of uterine contents if needed. Their use also considers whether the cervix is open and possible adverse effects.

Acute metritis and recurrent disease

A systemically ill mother may need fluids and other supportive care before further procedures. Some medicines used to empty the uterus can cause abdominal pain, vomiting, diarrhoea and faster breathing. This treatment may therefore be given in hospital to monitor adverse effects.

Follow-up ultrasound confirms treatment's effect on the uterus. For recurrent disease, removal of the uterus and ovaries is a common solution. If the uterine infection is pyometra, treatment is assessed separately as a serious pus-filled uterine infection.

Prevention

Previous failure to conceive, embryo resorption or many stillborn puppies warrants a planned reproductive examination before another attempt. The findings guide a plan for the next mating.

Uterine recovery after birth takes around 84 days, or almost 3 months. Very short intervals between seasons may therefore require skipping 1–2 seasons to allow recovery. Repeated cervical catheterisation can itself cause endometritis or pyometra. It is used selectively as part of justified investigation and treatment.

Important for dog owners

Records of seasons and previous pregnancies

Record the start dates of seasons, matings, insemination method, and ultrasound dates and results. Also note previous embryo losses, litter sizes and birth problems. Bring any available semen analysis results. Fertility assessment covers the male and arrangements for mating as well as the female. Suspected endometritis in the female does not remove the need to investigate other reproductive problems.

For a mother that has given birth, record discharge amount, smell and changes, along with appetite, general condition and care of her puppies. Contact a vet immediately if she becomes ill. After examination, ask which findings support further treatment and which test will establish the response. Also agree whether another breeding attempt is medically justified or removing the uterus is more appropriate for the mother. Recurrent endometritis may lead to removal of the uterus and ovaries.

Frequently asked questions

Is endometritis the same as pyometra?

Endometritis means inflammation of the uterine lining. Pyometra is a pus-filled infection of the uterus. Endometritis can present mainly as a fertility problem without systemic signs. Examination distinguishes changes in the lining, uterine contents and the severity of the mother's systemic illness so treatment suits the actual findings.

Can a dog look healthy despite an inflamed uterine lining?

Yes. Most females with endometritis may otherwise be clinically normal despite failure to conceive. Routine blood values can also be within reference ranges. Repeated reproductive failure is therefore investigated with targeted tests, rather than relying only on whether your dog seems ill at home.

Is vaginal bacterial culture enough for diagnosis?

Vaginal bacterial culture does not reliably reflect the uterine situation. Bacteria also occur normally in the vagina. Investigating endometritis may require a uterine cell or tissue sample, interpreted alongside cycle stage and other tests.

Does every case of endometritis need an antibiotic?

Not automatically. Not all uterine lining inflammation involves a demonstrated bacterial infection. Any necessary antibiotic is targeted using culture and susceptibility testing. Your vet also assesses whether the uterus contains fluid and whether other treatment or monitoring is needed alongside managing inflammation.

Can a female still have puppies after treatment?

This depends on the type of inflammation and other uterine changes. There is no single established biopsy grading scale that directly predicts future fertility. The response is checked by ultrasound. Removal of the uterus and ovaries may be recommended for recurrent disease.