Endometritis in Bitches: Diagnosis and Management

Endometritis in the bitch presents a diagnostic challenge because uterine inflammation may occur after mating, during the postoestrous period or persist as chronic disease, often without obvious systemic illness. The proposed classification into mating-induced, postoestrous and chronic endometritis reflects different possible routes and patterns of uterine inflammation, although their relative importance and progression are not yet fully established. For the clinician, recognizing persistent uterine fluid and reproductive failure can provide important clues. 

Mating-Induced Endometritis: When Physiological Inflammation Persists 

In species such as the bitch, semen is deposited directly into the uterus. Mating normally produces a short-term physiological inflammatory response, with uterine contractions and the immune response helping remove sperm, seminal fluid, inflammatory cells and microorganisms. When uterine clearance is impaired or the immune response is inadequate, the disturbed uterine environment may persist as mating-induced endometritis. 

Endometrial hyperplasia appears to be an important associated finding. Up to 40% of older bitches may have endometrial hyperplasia, and some bitches with mating-induced endometritis have concomitant hyperplasia. Delayed clearance of uterine fluid after breeding may result from physical obstruction to fluid flow and reduced uterine contractions, with increased PMN influx and a potentially less favourable uterine environment for embryos. 

Clinically, affected bitches may have a reduced chance of pregnancy or a smaller litter size. In one reported group of 14 recently mated bitches that failed to become pregnant, four (28%) had histologically diagnosed endometritis¹. 

Postoestrous Endometritis: Consider the Unmated Bitch 

Endometrial inflammation is not necessarily dependent on mating. During oestrus, the cervix is open, allowing the possibility of bacterial contamination of the uterus even when breeding has not occurred. This proposed mechanism may explain postoestrous endometritis in some bitches. 

This distinction is clinically relevant when investigating reproductive failure in an unmated bitch. A history of mating alone should not be considered essential for suspecting uterine inflammation, particularly when reproductive findings or imaging indicate delayed uterine clearance. 

Chronic Endometritis: Look for Persistence 

Mating-induced or postoestrous endometritis may potentially persist through the luteal phase and anoestrus into the next oestrous cycle. Chronic disease may also follow postpartum uterine infection. However, information on how frequently acute uterine inflammation progresses to chronic endometritis remains limited. 

Ultrasonographic persistence of uterine luminal fluid through the luteal phase and anoestrus can provide an important indication of chronic disease¹. Postpartum infection is another consideration because metritis following prolonged parturition, dystocia, retained foetal membranes or an unhygienic whelping environment may involve the entire uterine wall and produce significant systemic disease. 

Diagnosis: Combine Reproductive History with Imaging 

Diagnosis requires careful interpretation of reproductive history, clinical findings, and uterine imaging. In mating-induced cases, delayed clearance of uterine fluid can be detected by ultrasound. Endometrial hyperplasia may also be distinguished by the presence of small cysts¹. 

More detailed evaluation can demonstrate reduced uterine contractions and increased PMN accumulation following transcervical uterine sampling¹. Precise diagnosis of mating-induced and postoestrous endometritis requires uterine biopsy^1,2. 

For suspected chronic disease, ultrasound becomes particularly useful when uterine fluid remains detectable beyond the expected period of clearance. The diagnostic approach should therefore be guided by the reproductive stage and whether the suspected disease is postmating, postoestrous or persistent. 

Management Approaches and Therapeutic Considerations 

Treatment information for endometritis in bitches remains limited. Short-duration systemic antibiotic administration after mating has been associated with increased pregnancy rates in a small number of reports. These observations also support a possible role for bacteria in mating-induced endometritis. 

However, future management approaches may focus on improving uterine clearance rather than relying exclusively on antimicrobials. Ecbolic agents, non-antibiotic bacteriostatic approaches, and progesterone receptor antagonists have been proposed, but their efficacy requires further clarification. In chronic cases, one reported approach combining prebreeding systemic antibiotics, oxytocin, and uterine lavage successfully removed uterine fluid and, with repeated postbreeding treatment, allowed pregnancy to occur¹. 

Practical Clinical Insights 

When a bitch presents with reduced fertility or small litter size, consider uterine inflammation even when systemic signs are absent. Review the timing of mating or oestrus, assess the uterus ultrasonographically for persistent fluid and consider endometrial hyperplasia where appropriate. In suspected chronic cases, persistence of uterine fluid across reproductive stages strengthens the indication for further investigation. Because preventive and therapeutic evidence remains limited, management should be individualized according to the reproductive history, imaging findings and available diagnostic information. 

References 

1. Mir F, Fontaine E, Albaric O, Greer M, Vannier F, Schlafer DH, Fontbonne A. Findings in uterine biopsies obtained by laparotomy from bitches with unexplained infertility or pregnancy loss: an observational study. Theriogenology. 2013 Jan 15;79(2):312-22. https://www.academia.edu/download/99726774/j.theriogenology.2012.09.00520230312-1-ymweri.pdf 

2. Mir F, Fontaine E, Albaric O, Greer M, Vannier F, Schlafer DH, Fontbonne A. Findings in uterine biopsies obtained by laparotomy from bitches with unexplained infertility or pregnancy loss: an observational study. Theriogenology. 2013 Jan 15;79(2):312-22. https://www.academia.edu/download/99726774/j.theriogenology.2012.09.00520230312-1-ymweri.pdf