The veterinarian can be presented with a case of uterine prolapse under two conditions. The first is the prolapse that occasionally occurs under general anesthesia when the mare is in dorsal recumbency. The second is the prolapse that occurs during natural foaling. The former type of prolapse usually is associated with delivery of the fetus; it is secondary to the abortion or delivery and probably occurs because of the positioning and the relaxation of anesthesia. The uterus is usually undamaged by the prolapse and is easily replaced. The surgery table should be tipped to aid in the replacement of the uterus and towel clamps are often placed in the vulva. Once the mare recovers, reprolapse is usually not a problem; however, the uterus should be lavaged with sterile fluid to allow complete reduction of any horn eversion. Oxytocin should be given intramuscularly to assist in uterine involution.
Prolapse also occurs during foaling. Uterine prolapse associated with foaling is an emergency. At a minimum, the uterus can be severely damaged with negative effects on future fertility. It is not uncommon for a mare to hemorrhage sufficiently, usually from a uterine artery rupture, to die from hypovolemia. The prolapsed uterus should be protected, and suspended if possible, until it can be replaced. This author prefers general anesthesia for uterine replacement because it provides optimal control and relaxation of the mare, and it is a safer procedure for the personnel involved. Although anesthesia is a greater risk for the mare, this author believes that the benefits outweigh the risks.
The uterus must be cleaned and then replaced through the cervix. Topical treatments to remove uterine edema have not been useful in this author’s experience. Lubrication of the uterine tissues and manual compression seem to provide the most benefit. Obstetricians should be aware that during replacement it can often seem as though not much progress is being made, and then the uterus will seem to fall in place all at once. Persistence is the key to uterine prolapse replacement. Lavage and oxytocin should be provided as indicated above once the mare recovers from anesthesia.
Irritation to the anus that can result in straining and subsequent rectal prolapse is unusual after foaling but can occur. Most rectal prolapses are relatively short and result in a rather gruesome, doughnut-shaped mass of bloody tissue that protrudes from the anus. If the feces are soft enough, most mares can pass some fecal material through the prolapse. However, the appearance of the prolapse, and the associated straining, may necessitate surgical treatment under epidural anesthesia.
The clinician removes the edematous and hemorrhagic tissues by sharp dissection, leaving enough mucosa and submucosa to circumferentially suture without tension. Because the cranial rectum pulls orally once the edematous tissue is removed, the prolapse should be dissected free and then closed in quarters. This method facilitates exposure of the anastomosis site for the first three quarters of the circumference. Oral laxatives such as mineral oil and a nonsteroidal antiinflammatory will facilitate fecal passage. Short-term use of antimicrobials is at the surgeon’s discretion.
Bladder eversion also occurs as a result of straining of the urogenital tract. The everted surface of the bladder is covered with urothelium and is textured. If enough bladder is everted, the openings of the ureters can be seen at the cranial aspect of the everted tissue. To replace it, the bladder must be manually inverted back through the external urethral sphincter. The bladder is first cleansed and then is compressed between the surgeon’s hands and slowly pushed through the sphincter. Water-soluble sterile lubricants are very helpful, as is massage of the bladder to remove edema. If patient massage is unsuccessful in replacing the bladder, the external urethral sphincter can be transected dorsally to allow replacement. The incision must be closed to help keep the bladder from re-everting. The bladder should be lavaged with sterile fluid to ensure it is fully replaced and administration of antimicrobials with urinary excretion and a nonsteroidal antiinflammatory drug is recommended for several days.
Intact bladders prolapse as a result of a defect in the peritoneum and vaginal wall. This injury is the result of severe vaginal trauma. The bladder surface will be shiny, smooth, and white with visible subperitoneal vessels. The prolapsed bladder should be cleaned, and the bladder can be drained of urine by aspiration before replacement in the abdomen. A Foley catheter is then placed to keep the bladder decompressed. Urine drainage from the catheter will also reduce urine spillage into the vagina and subsequent contamination of the peritoneal cavity through the rent in the vaginal wall. Treatment of the vaginal wound involves reduction of further peritoneal contamination and prevention of eventration. The vaginal wound heals best by second intention. A cross tie can be used to prevent the mare from lying down; the possibility of eventration is thus reduced. Systemic antimicrobials should be administered.
Bladder rupture can occur either before, or more commonly after, foaling. The resulting uroperitoneum results in elevated serum levels of creatinine, blood urea nitrogen, and potassium, and lowered concentrations of sodium and chloride. Confirmation of urine in the abdomen makes the diagnosis, and the rent can be observed by an endoscopic examination of the bladder. Medical therapy requires urine drainage and correction of electrolyte abnormalities. Surgical access to the tear is impossible through a celiotomy, so reports of access for surgical repair of bladder ruptures are limited to either a colpotomy approach or to eversion of the bladder through the urethral sphincter. Both surgical procedures are technically demanding, as is a laparoscopic approach, which is unreported but may be possible in some instances. Conservative therapy for bladder rupture is successfully used in many species and may be of value in the mare. Medical therapy must be instituted, and the bladder is kept decompressed by the use of a self-retaining catheter such as a Foley.
Vaginal lacerations associated with eutocia are rare. When present, these lacerations are usually linear defects in the vaginal mucosa that heal by second intention and require no treatment. Occasionally an older mare will rupture a vaginal varicocele and cause hemorrhage. This injury is usually self-limiting, and treatment is unnecessary. Dystocias can cause severe vaginal lacerations, and their extent is dependent on the amount of vaginal trauma. The most common severe vaginal laceration is seen in primiparous mares when damage has occurred to the transverse urethral fold. The entire fold can be torn off or undergo necrosis, resulting in an incompetent external urethral sphincter. This laceration can result in urinary incontinence, scalding, and urine pooling. Immediate treatment for vaginal lacerations is gentle cleansing of the wounds, the use of a nonsteroidal, antiinflammatory drug, and topical emollients to reduce scarring and adhesion formation. Corticosteroids can be added to the topical medication to also reduce inflammation. Systemic antibiotics are indicated for mares with multiple or deep lacerations. Wounds are allowed to heal by second intention.
In mares with extensive vaginal adhesions or incontinence, surgical therapy is indicated after the wounds have healed. Both conditions have a guarded prognosis. The difficulty with treatment of vaginal adhesions is that they frequently reform. These adhesions seem to be most common in Miniature Horse mares, possibly because of the small pelvic canal in this breed, and the domed head of the fetus predisposes Miniature Horse mares to vaginal trauma. Sharp resection of adhesions followed by topical ointments with steroids may be beneficial. A vaginal vaultsized, soft tampon that is coated with ointment can be used to keep transvaginal adhesions from reforming.
Incontinent mares should have their caudal urethral sphincter pressure augmented. Because these horses are incontinent because of scarring and tissue loss, this procedure can be very challenging. Surgery should be considered only after all inflammation has subsided. The goal is usually to recreate a transverse urethral fold, as well as to extend the urethra in a similar manner to that performed to correct urine pooling.