Castration of the Vietnamese pot-bellied boar: 8 cases

Abstract

Surgical techniques for castration of the Vietnamese pot-bellied boar and outcome are described. Vietnamese pot-bellied pig (VPBP) boars (n = 8) were admitted for castration. Data retrieved from medical records (2002–2011) for these pigs included signalment, history, reason for castration, perioperative management, surgical technique, and complications. Follow-up information was obtained from owners. A scrotal approach with closed technique was used for 6 boars with normally descended testes. A scrotal approach and open technique was used in 1 inguinal cryptorchid boar. In a hemicastrated abdominal cryptorchid boar an ipsilateral parainguinal approach was used. No complications occurred. Castration of the Vietnamese pot-bellied boar is associated with minimal complications and a satisfactory cosmetic outcome. We recommend the routine closure of the external inguinal rings, a simple and fast procedure that may prevent post-castration inguinal herniation.

Introduction

Vietnamese pot-bellied pigs (VPBP) were introduced to North America in the 1980’s, and the number of these pigs kept as pets peaked during 1991 and 1995 (1–3). In 2002 there were 35 000 registered potbellied pigs and an estimated 200 000 unregistered pigs in North America (2,3). Both male and female pigs are kept as pets, and neutering animals of both sexes is highly recommended unless the intended use of the animals is breeding. Pot-bellied boars can reach puberty and display male behavior as early as 3 mo of age. They may also sire litters at this age, in contrast to boars of commercial breeds which do not reach puberty until 6 to 8 mo of age (4,5).

In order to reduce the expression of male behavior, castration of the VPBP boar has been recommended prior to onset of puberty, preferably between 2 d and 2 mo of age (3,6). Intact males may display an array of undesirable behaviors, including aggression towards humans and other pets, sexual behavior, and territorial marking with urine. The adult boar also develops an unpleasant odor and an enlarged preputial diverticulum, which accumulates a significant amount of pungent-smelling material (7).

Castration of commercial pigs in Europe and North America is usually performed by the farmer, and typically without any kind of anesthesia. The piglet is usually held by the hind limbs with the head down for the procedure (8,9). This type of restraint, however, carries a higher risk for complications when used on VPBP. Vietnamese pot-bellied pigs are usually older and heavier at the time of castration and it has been reported that they have weaker hind limbs than commercial pigs, putting them at risk of fracture and luxation (6). Additionally, surgical castration is a painful procedure and castrating piglets without the benefits of anesthesia or analgesia is an important animal welfare concern (10). Descriptions of the castration procedures in the pot-bellied pig are scarce in the literature, and a surgical technique similar to that used to castrate dogs has been reported (6). Scrotal and inguinal hernias are common in pigs; therefore, closure of the external inguinal rings may be prudent (11). Incorporation of the ligated spermatic cord in the external ring closure has also been described (6). To the authors’ knowledge there are no previously published case series describing castration techniques for Vietnamese pot-bellied pigs and postoperative results. The purpose of this report is to describe the techniques currently used at our institution for castration of the Vietnamese pot-bellied boar and the outcome in 8 cases. Surgical and post-operative complications as well as cosmetic appearance and effects on behavior are reported.

Materials and methods

Criteria for case selection

Medical records of Vietnamese pot-bellied boars that were admitted for castration to the Large Animal Clinic at the Ontario Veterinary College Teaching Hospital from January 2002 to 2011 were examined.

Retrieved data

Information collected from the medical records included patient age and body weight, history (including any display of undesirable behavior, and prior castration attempts), reason for castration, results of physical examination and preoperative blood tests, perioperative management, surgical technique, any additional procedures performed, and complications. Follow-up information was obtained by telephone interview with the owners and was available for all cases. Information requested included post-operative complications, cosmetic outcome, whether or not changes in behavior had occurred, and overall owner satisfaction.

Results

Eight Vietnamese pot-bellied boars [mean age of 10.2 mo (range: 2.5 to 39 mo) and mean body weight of 22.1 kg (range: 7 to 73 kg)] were identified. There were 6 boars with normally descended testes, 1 bilateral inguinal cryptorchid boar, and 1 unilateral abdominal cryptorchid boar (Table 1). In 5 cases the owner had complaints about undesirable behavior prompting them to castrate their pet. In 3 cases the pigs were castrated to prevent expression of male behavior and foul odor from the preputial diverticulum. Sexual excitement and sexual behavior directed towards humans, other pets, or household items were reported in 4 cases. Spraying of urine inside the house was reported for 3 cases; however, 2 of these pigs were not properly housebroken and urinated intermittently in the house. Aggressive behavior was reported in 3 cases. Aggression was directed toward dogs or household items in all 3 cases, and in 1 case the aggression was also directed toward the owners and manifested as biting. Three of the owners complained about a single type of undesirable behavior, while 2 pigs displayed multiple undesirable behaviors including sexual, aggressive, and marking behaviors or problems with urinating in the house.

Table 1.

Summary of 8 cases of castration of Vietnamese pot bellied pigs

Case	Age (months)	Weight (kg)	Previous or pre-operative behavior	Diagnosis	Surgical technique	Complications	Follow-up time (months)	Outcome
1	13	21	Spraying	Bilateral inguinal cryptorchid	Modified open — scrotal, closure of external inguinal ring	None	87.2	Resolved behavior
2	6	12	No complaints	Normally descended testes	Closed — scrotal, no closure of the inguinal ring	None	20	No initial behavior complaints
3	2.5	7.2	No complaints	Normally descended testes	Closed — scrotal, closure of the external inguinal ring	None	7.1	No initial behavior complaints
4	4	7	Sexual, aggressive and marking behavior	Normally descended testes	Open — scrotal, closure of the external inguinal ring	None	2	Resolved behavior
5	39	73	Sexual and aggressive behavior	Normally descended testes	Closed — scrotal, closure of the external inguinal ring	Hypothermia	3.6	Improved behavior, but aggressive towards dogs
6	8	37	Sexual behavior	Left abdominal cryptorchid — right testes removed earlier	Supra-pubic paramedian	None	2	Resolved behavior
7	3.75	7.5	Sexual, aggressive and marking behavior	Normally descended testes	Closed-scrotal, closure of the external inguinal ring	Hypothermia	2	Resolved behavior
8	5	12	No complaint, preventative measure	Normally desended testes	Closed-scrotal, closure of the external inguinal ring	None	2	No initial behavior complaints

Castration of the unilateral abdominal cryptorchid boar had been attempted by the referring veterinarian 1 mo prior to presentation. The descended testis had been removed but the non-descended testis could not be located using a scrotal approach. The bilateral inguinal cryptorchid was presented as an intact boar for a routine castration; however, during surgery both testes were found to be incompletely descended.

In preparation for surgery 7 of the pigs were fasted for 12 h, 1 pig was fasted for 4 h, and water was withheld from all pigs 2 to 3 h prior to surgery. Antimicrobials and non-steroidal anti-inflammatory drugs (NSAIDs) were administered perioperatively in 7 pigs. Information on medications was not recorded in 1 case. Four pigs were administered a single dose of either procaine penicillin G (20 000 to 40 000 IU/kg BW) IM (cases 3, 4, 5) or sodium penicillin IV (case 6). One pig (case 2) was administered a single IV dose of ceftiofur [2.0 mg/kg body weight (BW)] and 1 pig (case 8) was given a single IM injection of ceftiofur (3.0 mg/kg BW). Amoxicillin (50 mg/kg BW, PO, q8h) was administered to 1 pig (case 7) since this animal was already on treatment with amoxicillin for a traumatic wound to the left hind digit sustained 12 d prior to presentation.

Administered anti-inflammatory drugs included flunixin-meglumine (1.0 mg/kg BW, IV) in 1 pig (case 2), and meloxicam (0.4 mg/kg BW, IV) in 6 pigs (cases 3 to 8). Two pigs (cases 2 and 3) received a single injection of non-steroidal anti-inflammatory drugs (NSAIDs) preoperatively while 5 pigs (cases 4 to 8) were treated with oral meloxicam for 2 to 3 more days after surgery (0.4 mg/kg PO). Tetanus anti-toxoid (500 IU IM) was administered prior to surgery to 4 pigs (cases 3 to 6). Two pigs had been previously vaccinated against tetanus (cases 1 and 7) and therefore received no anti-toxoid. Two pigs (cases 5 and 8) did not receive anti-toxoid despite a lack of information about vaccination status. The pig in case 5 also received oral sucralfate (14 mg/kg BW, PO) the day of surgery and for 3 d post-operatively for gastric ulcer prophylaxis.

All pigs received preanesthetic medication by intramuscular injection of various drug combinations (Table 2). After the pigs were sedated, an intravenous catheter was placed in the auricular or the cephalic vein. Venous blood was then collected and blood gases and electrolytes, total solids, and packed cell volume were measured in all cases. No clinically significant abnormalities were detected in any of the pre-operative tests.

Table 2.

Drugs used for premedication and for induction of anesthesia in 8 Vietnamese pot-bellied pigs that were castrated

Case	1	2	3	4	5	6	7	8
Sedation premedication	Acepromazine (0.1 mg/kg BW) Ketamine (19 mg/kg BW) Butorphanol (0.19 mg/kg BW)	Midazolam (0.83 mg/kg BW, IM)	Butorphanol (0.55 mg/kg BW, IM) Midazolam (0.35 mg/kg BW, IM)	Butorphanol (1.14 mg/kg BW, IM) Midazolam (0.36 mg/kg BW, IM) Ketamine — Midazolam (1:1 mix 5 mL IM)	Butorphanol (0.4 mg/kg BW, IM) Midazolam (0.2 mg/kg BW, IM) Medetomidine (0.04 mg/kg BW, IM) Glycopyrrolate (0.004 mg/kg BW)	Butorphanol (0.2 mg/kg BW, IM) Medetomine (0.02 mg/kg BW, IM)	Ketamine (5.3 mg/kg BW) Butorphanol (0.2 mg/kg BW) Midazolam (0.2 mg/kg BW)	Butorphanol (0.1 mg/kg BW, IM) Midazolam (0.1 mg/kg BW, IM) Ketamine (4 mg/kg BW, IM)
Induction	No further medication given	Midazolam (0.2 mg/kg BW, IV) Propofol (3.3 mg/kg BW, IV)	Ketamine — Midazolam (1:1 mix 0.6 mL IV)	Ketamine — Midazolam (1:1 mix 5 mL IV) Ketamine (0.23 mg/mL IV)	Ketamine — diazepam (1:1 mix 3 mL IV)	Ketamine — diazepam (1:1 mix IV), amount given not recorded	Propofol (2.9 mg/kg BW, IV)	No further medication given as induction

General anesthesia in each case was induced with either a combination of injectable medications or inhalant anesthesia after direct intubation following initial deep sedation (Table 2). All pigs were orotracheally intubated and general anesthesia was maintained with isoflurane in 100% oxygen. The use of supplemental local analgesia with intra-testicular 2% lidocaine was recorded in 3 of the 8 cases (cases 2, 3, and 8).

Surgical technique

After induction of anesthesia the boars were placed in dorsal recumbency and the caudal ventral abdomen and ventral perineum were clipped and aseptically prepared. A scrotal approach and closed castration was used in 6 cases, while a scrotal approach and open castration was used bilaterally in the inguinal cryptorchid boar (case 1). For the scrotal approach, the testes were identified and manually pushed ventrally within the scrotum to tense the overlying scrotal skin. A 4-cm skin incision was made approximately 0.5 cm lateral and parallel to the median raphe, bilaterally. This incision was extended sharply through the subcutaneous tissue, tunica dartos and fascia. The testis within the vaginal tunic was then manually bluntly dissected from the surrounding fascia and exteriorized. In the bilateral inguinal cryptorchid (case 1) the parietal vaginal tunic was opened to allow accurate identification of all genital structures. In 2 cases (cases 5 and 7) the cremaster muscle was ligated and transected separately from the spermatic cord. A transfixation ligature was placed around the spermatic cord in all cases. The suture material used for ligation depended on the size of the cord and surgeon’s preference, varying from #3-0 to #0 absorbable mono- or multifilament. In the older and larger animals, (cases 5 to 7) the spermatic cord was transected with emasculators. In the other cases, (cases 1 to 4 and 8) the spermatic cords were crushed with Carmalt, Oschner or Kelly forceps, and then they were transected with a scalpel blade.

The external inguinal rings were slit-like openings, oriented in a craniolateral-to-caudomedial direction, and moderately large in proportion to the size of the animal. The rings were directly visible through the scrotal incisions after removal of the testes and consisted of pliable fibroelastic tissue, allowing some degree of manual expansion. The external inguinal rings were closed in 6 of the 8 cases to prevent post-operative inguinal herniation (Figure 1). In 1 pig the spermatic cord was double ligated, but the ring was not closed (case 2) and closure of the inguinal ring was not performed after the parainguinal approach in the unilateral cryptorchid boar (case 6). The external inguinal ring was closed using #2-0 or 3-0 absorbable suture in a simple interrupted or simple continuous pattern, followed by simple continuous pattern for closure of the subcutaneous tissues and intradermal/subcuticular suture pattern for closure of the skin.

Figure 1.

Closure of the external inguinal ring. Cranial aspect is to the top of the image. The lateral and the medial (black arrows) margins of the external inguinal ring are being sutured together.

Pre-operative inguinal and abdominal ultrasonography was performed in the abdominal cryptorchid to identify the location of the cryptorchid testicle (case 6). The abdominal testis was identified in the left caudal abdomen. A 4 cm parainguinal incision was made through the skin, rectus abdominus and peritoneum directly over the left testis. The testis was exteriorized with sponge forceps and the spermatic cord was ligated. The internal rectus sheath, including part of the rectus abdominal muscle and the external rectus sheath, were closed separately, followed by closure of the subcutaneous tissues and skin. No major complications occurred during surgery of either of these cases.

Postoperative care and follow-up

All pigs recovered well from general anesthesia with no major complications in the immediate post-operative period. Mild hypothermia [rectal temperature 34.6°C; reference range: 35.1°C to 39.5°C (12)], occurred in cases 5 and 7, and resolved after external warming with blankets and a heating device (Bair Hugger; Associated Health Systems, Surrey, British Columbia). Six of the 8 pigs were discharged the day of surgery.

Follow-up information was obtained from all owners at a mean of 2.8 mo after surgery (range: 2 to 87.5 mo). There were no complications related to the incision and all the owners were satisfied with the cosmetic outcome. No post-operative complications requiring veterinary care were reported in any case. Mild depression and lethargy after surgery was reported by 1 owner (case 7); however, this resolved within 24 h. Administration of oral meloxicam was considered acceptable for cases 4, 6, 7, and 8, but not for case 5.

All owners reported marked improvement or resolution of the undesirable behavior (days to weeks) after surgery. In most cases, mounting, destructive, and aggressive behaviors were not observed again after surgery. The pig in case 5, 3 y old at the time of castration, continued to display aggressive and destructive behavior the first 2 to 3 d after surgery. The destructive behavior resolved, but the pig remained aggressive towards dogs. The pig in case 7 continued to exhibit “food aggression” if disturbed during eating, according to the owner. The pig in case 6 had a single episode of mounting and ejaculating 3 d postoperatively, after which the behavior was not observed again. The 3 cases of urine spraying resolved shortly after surgery: the older animal discontinued the behavior immediately and the 2 younger pigs became properly housebroken.

Discussion

Based on our results, castration of the Vietnamese pot-bellied pig is a safe surgical procedure that has a high success rate in reducing unwanted behavior such as mounting and urine spraying. Even though the number of animals in this study was limited, we recommend that VPBP boars be castrated in the first year of life to ensure the best prognosis for a successful outcome.

Potential devastating complications following castration include herniation/evisceration, hemorrhage, and infection (13). No major intraoperative or postoperative complications were reported in this study. The lack of major surgical complications supports our conclusion that the described techniques are safe surgical options in these animals. Inadequate hemostasis is always a concern with castration, but the use of an appropriate crushing device, such as secure emasculators, as well as ligation of the cord minimize the risk of bleeding. In the small-sized pot-bellied pigs, Carmalt, Oschner, or Kelly or similar crushing forceps combined with ligation of the spermatic cords appeared to be sufficient to prevent hemorrhage.

Closure of the inguinal ring in the VPBP is a simple and rapid procedure that may help prevent post-castration herniation. Through the scrotal approach the external inguinal rings were readily identified and easily accessible for suturing. The rings appeared to be large in proportion to the animals’ size and in comparison with other species and this may account for the high rate of inguinal herniation in pigs. Inguinal and scrotal herniation is reported to be the most common defect observed in swine, with prevalence rates from 1.7% to 15% in commercial pig breeds (11,14). The prevalence of inguinal herniation has not been reported in the Vietnamese pot-bellied pig. The herniated viscus may be located within the inguinal canal or within the scrotal sac. A scrotal hernia can easily be identified but an inguinal hernia could be missed without thorough palpation. The scrotal approach was also effective for the bilateral inguinal cryptorchid (case 1). In this case the abnormal locations of the testes were first noted during surgery, but the anatomic characteristics of the inguinal rings permitted the successful removal of the testicles through the scrotal incision.

The abdominal cryptorchid in this study had been hemicastrated; however, it was uncertain which testicle was removed. Transabdominal ultrasonographic examination was performed and the testis was identified in the left caudal abdomen, directly adjacent to the body wall. The ipsilateral parainguinal approach was a simple, fast and minimally invasive technique that allowed excellent exposure of the testis and required minimal tissue manipulation. An inguinal approach has also been described in pigs (13); however, this approach was deemed inappropriate in this case since the left inguinal ring area had been explored during the first surgical procedure, and the authors felt that scar tissue was likely to be present and would impair dissection through the inguinal canal. Laparoscopic removal of abdominal testes is also an alternative that is particularly suited for show pigs for better cosmetic results (13). Laparoscopy offers the potential advantages of a lower incidence of incisional complications, faster recovery, and lower morbidity (less postoperative discomfort) (13).

Castration of the Vietnamese potbellied boar should be performed with the animal under general anesthesia with adequate perioperative pain management. The risks involved when manually restraining the boars and the unpredictable effect of intramuscular tranquilizers due to the thick layer of subcutaneous fat in pigs make general anesthesia with proper monitoring a more humane and safer choice for both the animal and the surgeon (6). These pigs are also regarded as pets by their owners, who expect similar levels of care as given to other companion animals. Complications during general anesthesia may occur and development of pneumothorax during mechanical ventilation has been reported; however, these were believed to be unique incidents (15). Malignant hyperthermia resulting from an inherited defect was suspected to have occurred in 1 Vietnamese pot-bellied pig (16). Symptoms and recommendations to manage this syndrome have been described (6). Management of perioperative pain included the administration of NSAIDs for most of the cases herein. A study examining post-operative pain in piglets castrated and sham-castrated with and without inhalant anesthesia or inhalant anesthesia and NSAIDs treatment (meloxicam) concluded that administration of NSAIDs was the only factor that significantly reduced post-operative pain, as measured by plasma cortisol-levels (17). A single dose of pre-operative antimicrobial treatment was administered to prevent surgical site infections (13).

Castration was effective in preventing and eliminating undesirable sexual and aggressive behavior in the male pet pigs in this study. The frequency of behavior problems in the general pet pig population is high, with human-directed aggression being the main concern (18,19). This is most often diagnosed as dominance aggression and is likely to be a multifactorial problem. It is suggested that the pig has stronger motivation than dogs to be dominant as this ensures the most food and the best chance of survival (18). Sexual behavior and aggression in the boar are linked to expression of male behavior and intact males are more aggressive and sexually active than castrates (20,21). Information on the duration of the behavior prior to the castration was not obtained in the cases reported here, but in the 2 older pigs, sexual and territorial behavior resolved after castration.

In conclusion, castration of the pet VPBP using the techniques reported here is a simple and safe procedure with minimal associated complications. Closure of the external inguinal rings is recommended to decrease the risk for potential catastrophic post-operative complications. Based on our results, gonadectomy appears to be effective in preventing and eliminating undesirable sexual and aggressive behavior in male VPBP; however, it might not be as effective in older animals. Further studies involving more animals are warranted.