Influence of breed and oestrous cycle on endometrial gland surface density in the mare.
BACKGROUND
The diffuse noninvasive epitheliochorial equine placenta develops an intimate and complex interdigitation with the maternal endometrium throughout gestation to maximise surface contact and, consequently, optimise nutritional and gaseous maternofetal exchanges. A significant reduction occurs in the surface density of microcotyledons on the placentae of Welsh Pony vs. Thoroughbred mares that may relate to a difference in either the number or density of endometrial glands between these breeds.


OBJECTIVE
To examine this hypothesis and to determine the influence of the oestrous cycle upon the development and surface density of endometrial glands.


METHODS
Endometrial biopsies were taken under videoendoscopic visual control from the base of a uterine horn from young, fertile, Welsh Pony and Thoroughbred mares at defined stages of the oestrous cycle. Computer-assisted morphometric analysis then permitted the surface density of endometrial glands within the stratum spongiosum to be assessed.


CONCLUSIONS
There was a statistically significant reduction in endometrial gland surface density in the Welsh Pony vs. Thoroughbred mares during both oestrus and dioestrus.


CONCLUSIONS
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.
University of Cambridge, Equine Fertility Unit, Mertoun Paddocks, Woodditton Road, Newmarket, Suffolk CB8 9BH, UK.
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Lefranc
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WR
Allen
D000818:Animals; D001947:Breeding; D004717:Endometrium / Q000473:pathology / Q000648:ultrastructure*; D004815:Epidermal Growth Factor / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D004971:Estrus / Q000502:physiology*; D005260:Female; D005333:Fetus / Q000098:blood supply; D006736:Horses / Q000235:genetics / Q000502:physiology*; D046529:Microscopy, Electron, Transmission / Q000662:veterinary; D010929:Placentation / Q000502:physiology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism
D012333:RNA, Messenger; D004815:Epidermal Growth Factor