75% of Vulva Below Pelvic Bone

The perineum is defined as the outer vulva, anus and surrounding area. The conformation of this area is important in the ability of the mare to maintain pregnancy. If the vulval seal does not function correctly, a condition termed pneumovagina (vaginal wind-sucking) may occur. Air (and bacteria) are sucked into the vagina and may colonize the cervix and internal reproductive tract leading to endometritis (infection of the uterus).

The ideal conformation is to have a vertical vulva with 75% below the pelvic bone. As the vulva angle becomes greater than 10-20% from the vertical, there is an increasing risk of fecal and urine contamination in the vagina (leading to endometritis) and/or wind sucking. Similar effects occur when the vulva is pulled back over the pelvic bone causing <75% to be below the pelvic bone.

The effect of poor confirmation can be corrected by cutting and suturing the upper vulva so that there is only a small hole for urination and artificial insemination (Caslick's operation). The vulva would then need to be cut for parturition or natural breeding.