The inner layer of the uterus is the endometrium. The activity of the glands in the endometrium is under hormonal control. This layer supports fetal growth, placental attatchment and development.

It is the endometrium (and some myometrium) which is sampled during uterine biopsy. A uterine biopsy may be done by your Veterinarian to determine if a uterine endometrial problem or infection exists in an infertile mare.