Equine Endometrial Gland Density and Endometrial Thickness Vary among Sampling Sites in Thoroughbred Mares

Abstract

The secretions of the equine endometrial glands are essential for the survival, growth, and development of the conceptus in early pregnancy, and endometrial gland density is directly related to successful pregnancy outcome. Endometrial biopsy is routinely used to assess the reproductive potential of broodmares. Some previous studies have shown that equine endometrial glands are uniformly distributed throughout the uterus; however, other work has shown variation of the endometrial architecture between biopsy sites, suggesting that a single biopsy is not representative of the entire endometrium. The aims of this study were to assess and compare the endometrial gland density and thickness at four sampling sites in the uterus (the central segment of each uterine horn, the uterine horn-body junction, and the caudal portion of the uterine body). Endometrial samples from five nulliparous Thoroughbred mares in diestrus were obtained at necropsy and used for subsequent histomorphometric analysis. The caudal uterine body had a significantly lower endometrial gland density and endometrial thickness than the other sites. This may result in nutrient deprivation and reduced survival of embryos or fetuses in this region of the uterus. The endometrial gland density and endometrial thickness did not significantly differ between the other regions sampled, indicating that they are similarly suitable for embryonic implantation and fetal development. Our results suggest that the endometrial structure of the caudal uterine body of the mare is not representative of the endometrial morphology at other sites. Thus, the caudal uterine body is not a suitable site for routine endometrial biopsy.

Keywords: endometrial biopsy; endometrial gland density; endometrial gland thickness; histomorphometry; nulliparous Thoroughbred mares.

Fig. 1.

Endometrial gland density at four regions of the uterus. The error bars indicate standard error (S.E.) Significant between-site differences are indicated by different superscripts (a, b) (p<0.05). A= left uterine horn, B=right uterine horn, C=uterine horn/body junction, D=caudal uterine body.

Fig. 2.

Endometrial thickness. The error bars indicate standard error (S.E.) Significant between-site differences are indicated by different superscripts (a, b) (p<0.05). A=left uterine horn, B=right uterine horn, C=uterine horn/body junction, D=caudal uterine body.

Fig. 3.

Correlation between the endometrial gland density and endometrial thickness. The correlation between endometrial gland density and thickness was almost statistically significant (Spearman’s correlation coefficient (r)=0.394, p =0.0856, n=20).