CHAPTER 28 Surgical Correction of Abnormalities of the Female Reproductive Organs
Uterine contamination following a breakdown of the anatomic barriers that protect the uterine environment is a common cause of subfertility in mares. In normal mares, uterine contamination is prevented by three anatomic structures: vulvar lips, vulvovaginal sphincter, and cervix.
Ideally, over 80% of the labia should lie in a vertical plane below the ischiadic arch of the pelvis. The Caslick index (La, where L = vulvar length and a = the angle of declination of the vulvar lips) has been developed to enable objective evaluation of the need for corrective surgery.1 Mares with an index above 100 may benefit from surgery and those with an index above 150 should definitely show improved fertility following surgery (Fig. 28-1).
The tightest seal is formed at the junction of the vestibule and the caudal vagina, near the urethral opening. Integrity of the seal depends on the paravaginal connective tissue and a thin muscle layer.
Infertility may result due to loss of cervical integrity, with infections manifested as a secondary complication. The cervix represents the last protective barrier between the uterus and the caudal portion of the tubular reproductive tract. A physiologic loss of integrity occurs during estrus, when the cervix dilates under the effects ofestrogen.
Dorsal displacement of the vulvar lips in relation to the ischiadic arch predisposes to pneumovagina, particularly in multiparous mares. With each pregnancy, the labia are pulled further dorsocranial, predisposing to aspiration of air and fecal contaminants into the vagina. Effective vulvar length also increases with age. Poor body condition reduces the amount of paravaginal fat and paravaginal muscle tone, drawing the anus cranially, thus predisposing to windsucking. Dystocia may stretch the perineal body, thereby disrupting integrity of the cranial vaginal seal. Perineal lacerations that disrupt the integrity of the vaginal wall and paravaginal tissue increase the risk of pneumovagina. Multiparous mares with poor vulvovaginal sphincter tone may aspirate air in the absence of a recessed anus, particularly during estrus. Cribbing mares with marginally normal perineal conformation may need episioplasty because negative pressure created in the abdominal cavity during cribbing pulls the anal sphincter cranially, predisposing to windsucking.
Owners should be instructed to have the episioplasty opened approximately 1 month prior to foaling, at the time the mare is vaccinated and dewormed. Opening of the episioplasty is accomplished by incising the sutured vulvar lips up to the dorsal commissure. A local anesthetic may be necessary.
In mares that have a very loose vulvovaginal sphincter along with a cranially displaced vulva, episioplasty may not prevent pneumovagina. For these mares, perineoplasty may be performed by resecting a portion of the dorsal vaginal wall and apposing the denuded tissue, resulting in narrowing of the caudal vagina.3
Urine pooling (vesicovaginal reflux) is a well-known cause of infertility. It is commonly encountered in multiparous mares because of relaxation of the ovarian and uterine ligaments. Other predisposing factors for urine pooling are weight loss, abnormal perineal conformation (recessed anus), and the combination of edema and relaxation of the reproductive tract that occurs during estrus or the early postpartum period. Mares that experience urine pooling due to poor perineal conformation should have Caslick’s surgery. Mares may pool urine only during estrus and suspect mares should be examined during standing heat. Several techniques have been described for surgical correction of the condition. The goal is to extend the existing urethra caudally. Three surgical approaches are described here; however, surgical corrections often fail postoperatively and must be repeated.
The mare is restrained in stocks, with or without tranquilization. Analgesia is achieved with epidural anesthesia. The rectum is emptied, and the tail is wrapped and tied out of the way with a rope attached around the mare’s neck. The vagina is cleaned with sterile lactated Ringer’s solution.
This technique is among the first described to extend the urethra.4 The urethral fold is pulled caudally, and its edges trimmed and sutured to incisions in the vaginal wall with No. 0 absorbable material. In most cases, caudal traction on the fold creates excessive tension and results in failure of the suture line. Additionally, it is difficult to achieve good apposition between the edges of freshened urethral fold and the vaginal wall (Fig. 28-4).
After placement of a 30 French Foley catheter in the urethra (Fig. 28-5, A), interrupted horizontal mattress sutures (No. 0 synthetic absorbable material) are placed in the vaginal mucosa, sparing the catheter. As the sutures are tightened, folds of mucosa close over the catheter. Adequate mucosa must be present on the formed crest to allow mucosal tissue to be trimmed. Following excision, a simple continuous suture pattern is used to appose the cut edges. After completion of the procedure, the catheter is removed (Fig. 28-5, B to F).
With this technique, the urethra is extended using vaginal mucosa. In contrast to other techniques, the denuded tissue present after forming the tunnel is not oversewn but is allowed to heal by second intention (Fig. 28-6, A to D).6
When a urethral catheter has been placed, it should be removed upon completion of the surgery because its presence may lead to excessive straining by the mare. Catheters tend to become rapidly obstructed by urinary crystals. Postoperative treatment should include administration of procaine penicillin G (20,000 IU/kg) for 5 days and tetanus prophylaxis. Mares should not be bred for at least 3 weeks. Thereafter, breeding management should include artificial insemination or hand breeding to prevent injury to the extended urethral fold during intromission.