Influence of breed and oestrous cycle on endometrial gland surface density in the mare

Abstract

A substantial upregulation of epidermal growth factor (EGF) mRNA in the epithelial cells lining the apical portions of endometrial glands has been demonstrated in pregnant mares between Days 35 and 40 after ovulation, coincident with the onset of interdigitation between the allantochorion and endometrium to form the microcotyledonary placenta. The increased surface density of endometrial glands noted in the uteri of Thoroughbred mares might account for the greater surface density of placental microcotyledons in this breed.

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

“…Some studies have compared the endometrial gland distribution at multiple endometrial biopsy sites in the mare, and they report that the endometrial glands are uniformly distributed throughout the uterus [4, 16, 19]. Based on these results, it has been concluded that differences in endometrial gland density of clinical samples are unlikely to be derived from the location of the biopsy site; however, other factors such as pregnancy, and seasonal and cyclical endocrine variations, can affect the endometrial architecture [4, 15].…”

“…These findings were based on 2-dimensional microscopic images of histological sections, which can be used to evaluate both the endometrial gland density and endometrial thickness [4, 15]. Recently, Lefranc and Allen used a computer-assisted morphometric method to measure the endometrial gland surface density in 3-dimensional microscopic images of 4 Welsh Pony mares that were necropsied during estrus [16]. Their results also support the clinical reliability of a single endometrial biopsy taken from any site in the uterus of the mare to assess the endometrial gland surface density [16, 17].…”

“…Recently, Lefranc and Allen used a computer-assisted morphometric method to measure the endometrial gland surface density in 3-dimensional microscopic images of 4 Welsh Pony mares that were necropsied during estrus [16]. Their results also support the clinical reliability of a single endometrial biopsy taken from any site in the uterus of the mare to assess the endometrial gland surface density [16, 17]. However, this technique is not able to estimate the endometerial thickness.…”

“…However, this technique is not able to estimate the endometerial thickness. This is a significant shortcoming as gland density is influenced by the endometrial thickness which varies with the estrous cycle and season [14,15,16,17]. In addition, the breeding histories of the mares were not reported [16, 17].…”

“…This is a significant shortcoming as gland density is influenced by the endometrial thickness which varies with the estrous cycle and season [14,15,16,17]. In addition, the breeding histories of the mares were not reported [16, 17]. Although these studies suggest that the uterine biopsy site is unimportant for clinical interpretation, other studies have shown variations in endometrial pathology between biopsy sites in the same mare [6, 7], and a single biopsy is not representative of the entire endometrium in mares with endometrosis [6, 7, 23].…”