CHAPTER 96 Reproductive Surgery in the Boar
Current swine breeding management strategies have placed an increased emphasis on the clinician’s technical proficiency in performing boar reproductive surgery. Use of surgically sterilized boars in gilt development and institution of estrus detection programs have become commonplace in many of today’s production systems. Critical, scrutinized genetic selection and the preferred distribution of these desired genetic traits through artificial insemination also have placed increased value on the boars that are standing at stud. It is not uncommon for boars selected for artificial insemination programs to have values 25 to 50 or more times greater than their market hog counterparts. These many varied factors contribute to the necessity for a clinician to be able to provide attention to the individual boar’s health and reproductive viability and function.
Most surgical procedures performed in adult boars require the use of general anesthesia.1–3 Drug combinations that have been used successfully to provide 30 to 60 minutes of general anesthesia include the following: (1) xylazine hydrochloride (2 mg/kg of body weight) plus tiletamine hydrochloride–zolazepam hydrochloride (Telazol*) (6 mg/kg), administered intramuscularly [IM]; (2) xylazine (1 mg/kg) plus butorphanol tartrate (0.1 mg/kg) plus Telazol (3 mg/kg), administered IM; (3) Telazol (5-ml vial) reconstituted with 2.5 ml of xylazine (100 mg/ml) and 2.5 ml of ketamine (100 mg/ml), with the resulting mixture given IM at a rate of 0.02 to 0.04 ml/kg; or (4) premedication with xylazine (2 mg/kg given IM), followed in 10 minutes with intravenous administration of a 5% solution of thiopental sodium, given to effect. Animals should be isolated from herdmates during the recovery period. With any of the surgical techniques outlined, it is preferable to keep recovered boars isolated from other swine for at least 10 to 14 days after surgery to allow healing. Exposed skin sutures should be removed before reintroduction to herdmates, because pigs are curious animals and frequently will pull or bite on the sutures.
Penile injuries are not that uncommon in the boar and often are related to facilities and management (e.g., bite wounds in boars kept in group housing or those used in pen and natural mating situations). Primary complaints that could signify a penile injury include the observation of blood in the urine or semen and hemorrhage from the preputial orifice. The challenge to the clinician in addressing penile injuries is the preoperative assessment of the condition to determine if sufficient damage has occurred to warrant medical or surgical intervention. Although penile injuries are not directly life-threatening, if they are not resolved quickly, the boar may become nonfunctional, leading to its early culling.
The penis is best examined while the boar is under general anesthesia. If the penis cannot be easily grasped and exteriorized using gauze pads, use of Bozeman’s atraumatic uterine dressing forceps (10.5-inch size) has been found to be helpful for this purpose. If damage to the penis is limited to abrasions or superficial lacerations, adequate sexual rest (for 3 to 4 weeks) is all that usually is required for healing. If, however, urethral patency has been compromised (i.e., fistula formation), especially if located in the body of the penis, surgical correction may be necessary. Trauma to the urethra requiring surgery should be dealt with quickly to avoid the need for excessive débridement. With the animal under general anesthesia, an 18 to 20 Fr Foley catheter is passed into the urethra to act as a stent. After cleansing and débridement, the urethra is closed with a 4-0 absorbable suture, swaged to an atraumatic needle, with a simple interrupted pattern that incorporates the mucosa. Fascia and skin are then closed using 4-0 nylon suture in a simple interrupted pattern. A Malecot drain inserted through a prepubic cystostomy may be used to divert urine from the reconstructed urethral site and thus promote healing; the drain is removed once healing is sufficient for normal micturition. A total of 4 to 5 weeks of sexual rest is recommended before the boar’s return to service.
Prolapse of the penis and preputial cavity mucosa have been reported after use of neuroleptics (i.e., acetylpromazine) or as a result of trauma to the penis during mounting activity. Penile prolapse should be considered an emergency situation, as additional injury to the penis is likely to occur the longer it remains prolapsed. The length of time elapsed since occurrence of the prolapse and the degree of insult to the prolapsed structures will determine the prognosis after correction.
With the animal under general anesthesia, the prolapsed tissues should be cleansed and examined for extent of injury. To reduce edema, the prolapsed tissues can be massaged during application of a topical antibiotic ointment. If the prolapsed tissues are too edematous to replace, compresses are applied for a short period of time before replacement is attempted. The prolapsed preputial mucosa and penis are then replaced into the sheath by gentle manipulation using the fingers rather than a surgical instrument. Correct repositioning has been accomplished when both the preputial mucosa and the penis are in place behind the ringlike division between the cranial and the caudal preputial cavities. To reduce the chance of postoperative recurrence, a temporary purse-string suture is placed around the preputial orifice. The suture is tightened sufficiently to retain prolapsed tissue but left loose enough to maintain patency for urination. If wounds or abrasions are present, the preputial cavity is flushed with a warm antiseptic solution; systemic administration of antibiotics and anti-inflammatory drugs over a 3- to 5-day period after replacement also is recommended. The purse-string suture is removed after a minimum of 14 days of sexual rest. Sexual rest may need to be extended an additional 15 to 45 days, depending on the severity of the wounds.
The frenulum is an epithelial attachment that runs from the mucosal covering of the penis to the base of the corkscrew behind the tip of the penis. This tissue normally is present in prepubertal and peripubertal boars, with breakdown and detachment occurring as a normal event in boars at or just before puberty. With failure of this breakdown process, the penis will “fishhook,” or turn backward, when penile extension occurs (Fig. 96-1). Boars with persistent penile frenulum cannot successfully initiate coitus but sometimes can have their semen collected using the gloved hand technique. Depending on severity, surgical correction of this condition can be performed either during semen collection or with the animal under general anesthesia. Resection or, better yet, removal of this tissue is most easily accomplished using scissors. Hemorrhage is minimal, negating the need for ligation before or after excision. The animal can be used for breeding 10 to 14 days after surgery. Because persistent penile frenulum is thought to be heritable, breeding stock should not be selected from the offspring sired by affected boars.
Prolapse of the prepuce in the boar is uncommon. In such an occurrence, however, quick action is paramount to successful replacement of viable tissue and minimization of edema. With the animal under general anesthesia, prolapsed tissue should be manually replaced. After replacement, a purse-string suture, using a 1 nonabsorbable monofilament suture, is placed around the preputial orifice. The purse-string suture should be tightened sufficiently to retain prolapsed tissue yet be loose enough to maintain patency for urination. Flushing of the preputial cavity with a warm, antiseptic solution is often performed daily over a 3- to 5-day period after replacement. At the end of treatment, the purse-string suture is removed, and the boar returned to service after an additional 14 days of sexual rest.
If the boar is presented with a prolapsed prepuce that is edematous and necrotic, surgical correction is warranted. With the animal under general anesthesia, the prolapsed tissue, prepuce, and preputial cavity are surgically prepared. A 1- to 2-cm-diameter tube is then introduced into the preputial cavity to act as a stent. Nonviable tissue is resected, with anastomosis of the two layers of the prepuce using a 1-0 absorbable, monofilament suture in an interrupted pattern. After anastomosis, antibiotic ointment is applied to the area, followed by replacement of the viable tissue back into the sheath. As a precaution, a purse-string suture is placed around the preputial orifice as described earlier. Concurrent removal of the preputial diverticulum should be considered to avoid potential complications associated with prepuce resection or amputation. Postoperatively, 4 to 6 weeks of sexual rest is recommended.