Eversion and prolapse of the vagina, with or without prolapse of the cervix, occurs most commonly in cattle and sheep. A form of vaginal prolapse, different in pathogenesis, also occurs in dogs (see Vaginal Hyperplasia in Small Animals). In cattle and sheep, the condition is usually seen in mature females in the last trimester of pregnancy. Predisposing factors include increased intra-abdominal pressure associated with increased size of the pregnant uterus, intra-abdominal fat, or rumen distention superimposed upon relaxation and softening of the pelvic girdle and associated soft-tissue structures in the pelvic canal and perineum mediated by increased circulating concentrations of estrogens and relaxin during late pregnancy. Intra-abdominal pressure is increased in recumbent animals. Added to this, sheep tend to face uphill when lying down, so gravity contributes to vaginal eversion and prolapse. Docking the tails of lambs may damage structures that support the pelvic girdle (eg, coccygeus muscle) and predispose to vaginal prolapse if the tail is docked too short. The tail should be removed at the level of the ventral skin fold, leaving two or three coccygeal vertebrae intact.
The prolapse begins as an intussusception-like folding of the vaginal floor just cranial to the vestibulovaginal junction. Discomfort caused by this eversion, coupled with irritation and swelling of the exposed mucosa, results in straining and more extensive prolapse. Eventually the entire vagina may be prolapsed, with the cervix conspicuous at the most caudal part of the prolapsus. The bladder or loops of intestine may be contained within the prolapsed vagina. As the bladder moves into the prolapsed vagina, the urethra may be occluded. The bladder then fills and enlarges, which hinders replacement of the prolapsed vagina unless the bladder is first drained. The bladder may even rupture with potentially fatal consequences. Vaginal prolapse may be graded as I (intermittent prolapse, especially when recumbent), II (continuous prolapse), III (continuous prolapse of vagina, bladder, and cervix), or IV (grade II or III with tissue damage by trauma, infection, or necrosis).
Although most common in mature animals in late pregnancy, vaginal prolapse can occur in young, nonpregnant ewes and heifers, especially in fat animals. Predisposing factors include grazing estrogenic plants (especially Trifolium subterraneum) or exogenous administration of estrogenic compounds (usually in the form of growth-promotant implants). Cervicovaginal prolapse is more common in stabled than in pastured animals, suggesting that lack of exercise may be a contributing factor. Vaginal prolapse may also be a problem in cows subjected to repeated superovulation for embryo recovery due to repeated exposure to supraphysiologic concentrations of estrogens. A genetic component in the pathogenesis of cervicovaginal prolapse is likely, because a breed predisposition exists in both cattle (Brahman, Brahman crossbreds, Hereford) and sheep (Kerry Hill, Romney Marsh). In pigs, vaginal prolapse is often associated with estrogenic activity of mycotoxins.
For replacement of the prolapsed vagina, an epidural anesthetic is first administered. The organ is washed and rinsed, and the bladder emptied if necessary. Usually, this can be achieved by elevating the prolapsus to allow straightening of the urethra; occasionally, needle puncture through the vaginal wall may be necessary. The vagina is well lubricated (glycerol provides lubrication and reduces congestion and edema by osmotic action) and replaced and then held in position until it feels warm again.
Retention is achieved by insertion of a Buhner suture—a deeply buried, circumferential suture placed around the vestibulum to provide support at the point at which the initial eversion of the vaginal wall occurs. The Buhner suture has largely superseded earlier attempts to prevent prolapse by various patterns of sutures in the vulvar lips (which do not prevent the initial eversion of the vagina into the vestibulum) or by methods that relied on placement of a retention device within the vagina (which tend to cause discomfort and further straining). Buhner sutures should generally be removed before parturition to prevent extensive laceration. Modification of the Buhner suture to include an exposed, horizontal mattress–like suture has the advantage of remaining in place even when vestibulovaginal tissues have little holding power, and a traditional Buhner suture may be prone to tear through the dorsal or lateral vestibular wall. The Buhner suture and its modifications attempt to replicate the support normally provided by the constrictor vestibuli muscles that are lacking in cases of prolapse. Permanent fixation of the vagina can be achieved by the Johnson button technique, whereby sutures are placed from the vagina, through the sacrospinotuberal ligament and gluteal muscles, and then anchored in the vagina and on the skin with large, flat discs. This can also be accomplished by anchoring the cervix to the prepubic tendon or iliopsoas muscle. Although the cervical os may be edematous and inflamed, cervicovaginal prolapse seldom interrupts pregnancy and does not specifically predispose to dystocia or postpartum uterine prolapse, which has a different etiology.
Vaginal prolapse in sheep may occur simultaneously in many ewes as a herd problem, making surgery impractical. In these cases, use of a commercially available vaginal retention device (a bearing retainer) may be useful. Sheep may lamb without mishap with these devices in place. Permanent fixation techniques (cervicopexy or vaginopexy) have been described in which the cervix or vaginal wall is anchored to other pelvic structures. They may be useful in individual cases of chronic or recurrent prolapse, but most cases are resolved by a well-placed Buhner suture.