Histological Studies in the Endometrium of Fertile and Subfertile Bitches

Endometrial biopsies have been used historically as a diagnostic tool as part of breeding management in some domestic species. In the mare, the findings in an endometrial biopsy can relate to the ability of that mare to carry a pregnancy to term. The value of the endometrial biopsy in the canine has not been fully established. In this study, the presence of inflammation, fibrosis and endometrial cysts was characterised in full-thickness uterine biopsies from subfertile bitches in late diestrus/early anestrus and compared to the same findings in fertile bitches. The hypothesis was that subfertile bitches would have more inflammation, fibrosis and endometrial cysts. Full-thickness uterine biopsies were taken at the hysterotomy site at the time of C-section for control cases (n = 103), and previous submissions were collected from The Ohio State Reproductive Service as subfertile samples (n = 263). The cases were blinded, randomised and evaluated. Chi-squared or Fisher's exact tests were used to compare categorical variables between control and experimental samples. The Wilcoxon rank-sum test was used to compare ages between the groups. Overall, inflammation was observed more frequently in the subfertile group in comparison to the control group. Lymphoplasmacytic inflammation was observed more frequently in the subfertile group when compared to the fertile group. The incidence of periglandular fibrosis and endometrial cysts was not significantly different between the two groups. These results indicate that microscopic evaluation of canine uterine biopsies may be more suited to detecting inflammatory changes in the endometrium and isolated endometrial cysts, as well as isolated fibrotic lesions, which may be less impactful on fertility compared to chronic inflammation.