Uterine cytology is a common diagnostic test that provides information about the health of a mare's uterus and the current stage of their heat cycle. It involves the examination of uterine lining cells that have been collected on a swab. The laboratory work is typically done in an equine hospital, so there is little delay in receiving the results. It is an important complementary test to the uterine culture.

This procedure involves sterile technique, wherein a cotton swab or cytology brush is passed through the cervix and into the uterus. It is rolled around to collect cells and removed. The swab is carefully smeared onto a slide, stained and examined under the microscope. Uterine lining cells and inflammatory cells are typically seen. The ratios and characteristics of those cells indicates different stages and health of the uterine environment.