The vulva is the exterior portion of the reproductive tract which protects the entrance into the vagina. The vulva is 2-3 in. (5-7 cm) below the anus and 5-6 in. (12-15 cm) in length. The labia are the lips of the vulva which should come to together cleanly to keep the entrance to the reproductive tract closed so that contamination with feces does not occur. The vulva is kept closed by the vulva-constrictor muscle which is located just inside the labia. It is this muscle which opens and closes the vulva during the estrus behavior known as winking.

Opening the vulvar lips exposes the clitoris. This organ is composed of erectile tissue with the same embryonic origin as the penis. There are three pockets around the clitoris which provide an ideal environment for bacteria infections such as Taylorella equigenitalis (causes contagious equine metritis (CEM)), Klebsiella pneumoniae and Pseudomonas aeruginosa. Bacteria cultures of swabs from the clitoral sinuses are used to document that the mare is free from CEM.