Eversion and prolapse of the vagina, with or without prolapse of the cervix, occurs most commonly in cattle and sheep (cows and ewes) and usually occurs in mature animals in the last trimester of pregnancy. A form of vaginal prolapse also occurs in dogs.
Predisposing factors include increased intra-abdominal pressure associated with the gravid uterus, intra-abdominal fat, and rumen distention plus relaxation and softening of the pelvic girdle and associated soft-tissue structures of the pelvic canal and perineum mediated by increased circulating concentrations of estrogens and relaxin during late pregnancy. Increased intra-abdominal pressure in recumbent animals may contribute to eversion of the vaginal tissue. 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 excessively. Therefore, 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 visible at the most caudal part of the prolapsed tissue. 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 correction of the vaginal prolapse unless the bladder is first drained. The bladder may even rupture with potentially fatal consequences.
Vaginal prolapse may be categorized as:
Grade I: intermittent prolapse; often visible only when recumbent, vaginal tissues may appear normal
Grade II: continuous acute prolapse of vaginal tissue
Grade III: continuous acute prolapse of vagina, bladder, and cervix
Grade IV: chronic prolapse of either grade II or III with resultant 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 affected tissues are lavaged, and the bladder emptied if necessary. Usually, this can be achieved by elevating the prolapsed tissue to allow straightening of the urethra; occasionally, needle puncture through the vaginal wall may be necessary. The vagina is well lubricated 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. This purse-string suture should be tightened to allow enough of an opening at the ventral commissure for urination (~3–4 cm or 2–3 finger widths). The Buhner suture or variations including a horizontal mattress or shoelace pattern have largely superseded methods that relied on placement of a retention device within the vagina (which tend to cause discomfort and further straining).
A 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. The traditional Buhner suture may be prone to tearing through the tissues of the dorsal or lateral vestibular vaginal wall. The Buhner suture and its modifications attempt to replicate the support normally provided by the constrictor vestibuli muscles that are weakened in patients with prolapse. Animals with Buhner sutures should be monitored closely for signs of parturition so sutures may be removed prior to delivery to prevent extensive laceration of the vagina and vulva.
Permanent fixation of the vagina can be achieved by means of the Johnson button technique, whereby sutures are placed via the vagina, through the sacrospinotuberal ligament and gluteal muscles, and then anchored in the vagina and the skin with large, flat discs. This can also be accomplished by anchoring the cervix to the prepubic tendon or iliopsoas muscles. Fixation using the Johnson button technique allows for parturition to proceed unimpeded by the vaginopexy. 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 surgical treatment 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. Such procedures may be useful in individual animals with chronic or recurrent prolapse, but most cases are resolved by an appropriately placed Buhner suture.
Complications may arise if the vaginal prolapse is not treated promptly; these include peritonitis and vaginal wall rupture. The latter can lead to evisceration in the affected animal requiring humane euthanasia. In cattle and sheep, vaginal prolapse has a hereditary component and therefore is likely to recur in subsequent pregnancies. Due to the likelihood of recurrence, females with vaginal prolapse should be culled from the herd or flock.