Uterine biopsy is a common diagnostic test performed on mares to assess uterine health and the ability of a mare to carry a foal to term. It is performed in the standing, often unsedated, mare and is considered minimally invasive.

This procedure involves sterile technique and long-handled cutting forceps called a uterine biopsy instrument. The vet passes the instrument through the cervix into the uterus. One or more pieces of the uterine tissue (endometrium), are sampled and placed in formalin. This tissue is sent to a reproductive laboratory where it is examined under the microscope for abnormalities and scored based on a set of characteristics. This biopsy can be repeated after treatment to assess improvement.