Overview
The mare's uterus hangs from the roof of the abdomen and pelvis by the broad ligament (mesometrium), which attaches to the dorsal curvature of the horns; the ventral curvature is free. Outside pregnancy, the body and horns lie mainly in the abdomen, in front of the pelvic inlet, resting on the intestinal loops; the small colon and rectum lie dorsally.
Parts
- Horns (cornua uteri): relatively short, they diverge from the body almost straight towards the ovaries, without coiling. Their base is where the embryo becomes fixed.
- Body (corpus uteri): long and wide, nearly as long as the horns; this is the most visible difference from the cow.
- Endometrium: with longitudinal folds and no caruncles. The placenta is diffuse and epitheliochorial, with microcotyledons spread over the whole chorion. Early in pregnancy, trophoblast cells invade the endometrium and form the endometrial cups, which produce equine chorionic gonadotropin (eCG).
- Cervix (cervix uteri): short, soft-walled, with longitudinal folds that continue into the vagina; it relaxes in oestrus and admits one or more fingers, which makes transcervical techniques easy.
Clinical relevance
- Pregnancy diagnosis: transrectal ultrasound detects the embryonic vesicle from two weeks. The vesicle is mobile until it becomes fixed at around day 16 at the base of one horn.
- Twin pregnancy: the mare tolerates it poorly (abortion or weak foals); it is therefore looked for at the first scans and one vesicle is reduced, ideally before fixation.
- Endometritis: persistent post-breeding endometritis affects mares with poor uterine clearance; it is treated with lavage and oxytocin. Endometrial biopsy grades fibrosis and inflammation and guides the fertility prognosis.
- Ascending placentitis: enters through the cervix and causes abortion or weak foals.
- Retained placenta: if the membranes are not passed within about 3 hours of foaling they are considered retained; it may be followed by metritis, endotoxaemia and laminitis.
- Uterine torsion: in late pregnancy; it causes colic and is diagnosed by rectal palpation of the taut, crossed broad ligaments.