Multicenter retrospective study of complications and risk factors associated with castration in 106 pet pigs

Abstract

Castration of pet pigs is becoming a commonly performed procedure. However, little information is available regarding surgical techniques and complications. Medical records of 106 pet pigs admitted to 3 teaching hospitals for castration were reviewed. All descended testicles were approached via pre-scrotal skin incisions, which were either closed (59.4%) or left open (22.6%). The inguinal rings were closed in 42% of cases. Of the 106 pet pigs, 4.7% developed a complication after surgery, which consisted of peri-incisional swelling. Pigs which underwent inguinal ring closure were 6.6 times more likely to develop a post-operative complication (confidence interval: 1.16 to infinity, P = 0.035). Age and weight at time of castration were not significantly associated with complications (P = 0.698 and P = 0.685, respectively). The results from this retrospective study suggest that castration in pet pigs is a safe procedure with a minimal rate of complications.

Introduction

Minipigs and Vietnamese pot-bellied pigs have become increasingly popular as domestic pets in North America in the last decades (1). With this rise in popularity there has been an increased demand for veterinary medical care and routine reproductive sterilization surgeries such as ovariectomy, ovariohysterectomy, and castration (2,3).

Castration of the pet pig has been recommended before the onset of puberty, which can occur as early as 3 mo of age, to decrease the risks of aggression towards humans and other pets, reduce sexual behavior, and prevent marking with urine (4). It is also beneficial in reducing the development of the preputial diverticulum, which may accumulate unpleasant malodorous material (5).

While pet pig castration is commonly performed, limited information is available regarding surgical techniques and complications. A scrotal approach with closed and open skin incisions has been described in a case series of 8 Vietnamese pot-bellied boars with minimal complications and satisfactory cosmetic outcomes (4). A laparoscopic-assisted technique has also been reported in 2 cases to remove abdominally located cryptorchid testicles (3). The objective of this study was to describe the surgical techniques used at 3 teaching hospitals, report associated complications, and identify potential risk factors for complications in pet pigs that underwent castration. We hypothesized that castration via a pre-scrotal approach with skin incisions closed or left open would be associated with a low incidence of complications. In addition, we hypothesized that cryptorchid castrations via a para-inguinal approach would also have a low incidence of complications.

Materials and methods

Case selection

Medical records of pet pigs presented between January 2009 and December 2017 at 3 teaching hospitals (School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin; College of Veterinary Medicine, University of Tennessee, Knoxville, Tennessee, and the Ontario Veterinary College, University of Guelph, Guelph, Ontario) were reviewed. Pet pigs (defined as an animal not used for production) presented for castration under general anesthesia were included. The following information was obtained from the medical records: reason for castration, signalment (including age, sex, weight, and breed), intra-operative data with respect to surgical approach, presence or absence of descended testicles, surgical time and anesthesia time. Intra- and post-operative complications, peri-operative care, length of hospital stay, and short-term survival, defined by hospital discharge, were also obtained.

Surgical procedures

The procedures were performed with the pigs anesthetized and positioned in dorsal or lateral recumbency. The caudal ventral abdomen and/or perineum was clipped, aseptically prepared, and draped according to hospital protocols. Lidocaine 2% was injected into the descended testicle with a volume according to the size of the pig (3 to 5 mL).

All descended testicles were approached with 1 or 2 parallel pre-scrotal skin incisions. Pressure was applied on the scrotum to position 1 testicle to the pre-scrotal area. The skin and subcutaneous tissues were incised along the median raphe or parallel to the median raphe over the displaced testicle. The incisions were continued over the spermatic fascia and the testicle was exteriorized by manual dissection of the surrounding soft tissues. A transfixation ligature was placed proximal to the testicle on the spermatic cord. The suture material used for ligation varied between USP size 2-0 to 1 polyglactin 910 or polydioxanone depending on the size of the pig. The spermatic cord was then crushed with Carmalt or Kelly forceps distal to the ligature and then transected sharply with a scalpel blade. The procedure was repeated for the second testicle. In the cases presented for inguinal hernia or when the inguinal ring was observed to be subjectively larger, the external inguinal rings were closed using USP size 2-0 or 3-0 glycomer 631, poliglecaprone 25, or polydioxanone.

The surgical incisions were closed in 2 layers or stretched manually and left open, according to clinician’s preference. When the incisions were closed, the subcutaneous tissues were sutured in a simple continuous pattern with USP size 2-0 polyglactin 910 or polydioxanone. An intradermal/subcuticular suture pattern or simple continuous suture pattern was used for closure of the skin with USP size 3-0 or 2-0 glycomer 631 or poliglecaprone 25. Incisions were left uncovered or a non-woven adhesive wound dressing (Primapore; Smith & Nephew, Watford, Hertfordshire, UK) was applied.

For cryptorchidectomy, a para-inguinal approach was used. The skin incisions were made medial and parallel over the cranial aspect of the external inguinal ring. A 3- to 4-cm incision was made in the aponeurosis of the external oblique muscle and the index and middle fingers were bluntly inserted and pushed through into the internal abdominal oblique muscle, retroperitoneal fat, and peritoneum. The internal inguinal ring was identified, and the retained testicle was located and exteriorized. A transfixation ligature was placed and the testicle was removed as previously described for descended testicles. The abdominal wall was closed in a simple continuous pattern with USP size 2-0 to 2 polyglactin 910. The subcutaneous and intradermal layers were closed and the descended testicle was castrated as previously described. The incision was left open to heal by second intention.

Peri-operative care

Pigs were kept off feed 12 to 24 h before surgery, and in a few cases they were also kept off water. Antimicrobials and non-steroidal anti-inflammatory drugs (NSAIDs) were administered before or both before and after surgery according to clinician’s preference.

Patients were discharged from the hospital the day after surgery if no complications were encountered. Restricted exercise was recommended for 2 wk or until there was complete healing of the incisions.

Data analysis

Descriptive data were generated in commercial statistics software (STAT/STAT, version 9.4; SAS Institute, Cary, North Carolina, USA), and results were reported as mean ± standard deviation (SD) and range. Exact conditional logistic regression was used to determine risk factors of complications. Statistical significance was identified at the significance level of P < 0.05.

Results

Signalment and history

Pet pigs (N = 106) were included in the study. There were Vietnamese pot-bellied pigs (n = 69), miniature pigs (n = 16), Hampshire (n = 9), unknown breed (n = 9), and Yorkshire, Landrace, and mixed breed (n = 1 each). Mean age was 6.2 mo ± 10.7 mo (range: 1 to 84 mo). Mean body weight was 22.4 kg ± 44.9 kg (range: 2.8 to 350 kg). Age and weight at time of castration were not significantly associated with complications (P = 0.698 and P = 0.685, respectively). In 7 cases the reason for castration was a behavioral problem and in 3 cases it was due to an inguinal hernia; the rest were presented for routine elective castration. Ninety-one pet pigs had normally descended testicles and 15 were cryptorchid (14% of the population). Fourteen were unilateral (7 right, 7 left) and 1 bilateral cryptorchid.

Surgical procedure

The surgeries were performed with inhalant anesthesia in 91.5% (97/106) and intravenous anesthesia in 8.5% (9/106) of the cases. All were initially sedated with different protocols of intramuscular medications. The mean duration of surgery was 49 min ± 16.3 min (range: 20 to 95 min), and mean duration of anesthesia was 80 min ± 27.3 min (range: 40 to 150 min). If only castrations with 2 descended testes were considered, the mean duration of surgery was 47 min ± 16.9 min (range: 20 to 95 min) and the mean duration of anesthesia was 77.9 min ± 25.3 min (range: 40 to 150 min). For the cryptorchidectomies, the mean duration of surgery was 55 min ± 11 min (range: 40 to 85 min) and the mean duration of anesthesia was 93.6 min ± 26.6 min (range: 55 to 140 min).

Two pigs were diagnosed during surgery with testicular abscesses, both of which were unidentified before the procedure. No history related to the abscesses was reported in the records. One of the pigs had sustained an accidental puncture of the abscess during the castration procedure; however, no major contamination was associated with the incident as the puncture occurred externally to the body. This was the only intra-operative complication encountered, accounting for an intra-operative complication rate of < 1%. Additionally, 1 cryptorchid pig was presented with the right testicle adhered to the bladder. This was considered an incidental finding and that testicle was removed without complications.

Forty-two percent of the cases (45/106) had the inguinal rings closed; this included all the pigs presented for inguinal hernias. In 58.5% (62/106) of cases the incisions were closed in 2 layers with an intradermal suture pattern, in 0.94% (1/106) of cases the skin was closed in a simple continuous pattern and in 22.6% (24/106) of cases the incisions were stretched manually and left open. Details regarding the surgical closure were not recorded in 19 cases.

All pigs recovered from anesthesia. Complications during and after anesthesia included: hypotension 5.7% (6/106), hypertension 1.9% (2/106), hypoglycemia 1.9% (2/106), and rough recovery 3.8% (4/106). Overall rate of anesthetic complications was 13.2% (14/106).

Peri-operative care

Sixty-seven pigs received flunixin meglumine (Flunixin Injection; Zoetis, Kirkland, Quebec) 2.2 mg/kg body weight (BW), IV, 29 were given meloxicam (Metacam; Boehringer Ingelheim, Burlington, Ontario), 0.4 mg/kg BW, IV, 4 received carprofen (Rimadyl; Zoetis), 2 mg/kg BW, PO, and 4 did not receive any anti-inflammatory drugs. Administration of NSAIDs was not documented in 2 cases. Thirty-nine pigs received ceftiofur (Excenel; Zoetis), 3 to 5 mg/kg BW, SC, 23 pigs received long-acting ceftiofur (Exceed; Zoetis), 2.7 mg/kg BW, IM, 11 received ceftiofur and potassium penicillin (Penicillin; Fresenius Kabi, Toronto, Ontario), 20 000 to 40 000 IU/kg BW, IV, 16 procaine penicillin (Depocillin; Merck, Kirkland, Quebec), 20 000 to 40 000 IU/kg BW, IM, 1 received amoxicillin (Amoxil; Aurobindo, Woodbridge, Ontario), 20 mg/kg BW, PO, 1 received amoxicillin and clavulanate (Clavamox; Zoetis), 5 mg/kg BW, PO, and 4 pigs did not receive any antimicrobials. The use of antimicrobials was not documented in 11 cases.

Hospitalization was 2.6 d ± 2.2 d (range: 1 to 15 d). One pig stayed for 15 d at the request of the owner; this was not associated with any complication. All 106 pigs were discharged from the hospital. None of the variables showed any significant effect on complication rates.

Post-operative complications

Five pigs experienced post-operative complications (complication rate: 4.7%,). All complications consisted of mild periincisional swelling, none of which required major veterinary attention. Interestingly, in all of those cases inguinal ring closure was performed during the procedure. Patients which underwent inguinal ring closure were 6.6 times more likely to present with a postoperative complication [odds ratio (OR): 6.6, 95% confidence interval (CI): 1.16 to infinity, P = 0.035].

Discussion

To our knowledge, there is no large retrospective case series describing the surgical techniques and post-operative complications after surgical castration in pet pigs. The technique described here for descended testicles is similar to the pre-scrotal approach described for dogs. It is the most common and easily performed technique used for castration in that species (6). However, there is limited information comparing this technique with other approaches. The scrotal approach has been described and is thought to be quicker, but post-operative drainage is more common (7). There is a wide variety of conditions to which pet pigs will be returned once they are discharged from the hospital. We believe that the post-operative environment for most pet pigs is similar to that of dogs. However, not all pigs are household pets and some of them live in barn settings. Our records did not indicate the housing of our patients; therefore, we cannot comment if there was an association with housing conditions and complication rate with the use of a pre-scrotal approach. It might be suspected that pigs housed on straw or shavings in barn environments may be more at risk for incisional infections. Further studies are warranted.

Most of the pigs included in this study (91%) were presented for routine castration. Other reasons for castration included behavioral problems and inguinal herniation, which was observed in 2.8% of our population (3 cases). A high rate of inguinal herniation has been reported in pigs, with a prevalence of 1.7% to 6.7% in commercial breeds (8). Fifteen pigs were presented for cryptorchidism. To our knowledge, there are no reported numbers of the specific prevalence of the condition in pet pigs. However, in production pigs the prevalence has been reported to range from 4% to 12% (9). This is comparable to the 14% prevalence encountered in our population. Based on a study in Duroc swine, it has been postulated that cryptorchidism is related to a homozygous recessive trait (5). In a study by Scollo et al (10) the undescended testicle was located in the abdomen in 90.8% (258/284) of cases and in the inguinal region in 9.1% (26/284). Unfortunately, information was lacking from the medical records regarding the location of the undescended testicle for many of the cases in our population. However, based on the reported para-inguinal approach, it can be concluded that most of these were abdominally located.

In 2 of the cases herein, intra-operative testicular abscesses were found that had not been previously identified on physical examination. Brucella suis can be localized in the pig testicles (11). Clinical evidence of this pathology is infrequent; orchitis and epididymitis can be subclinical and lesions such as hypertrophy or abscesses can be observed (11). Brucella suis is a significant zoonotic pathogen; therefore, samples for bacterial culture should be submitted when an abscess is observed in pig testicles (12). Further research is warranted in pet pigs in order to appropriately manage these cases. Unfortunately, no bacterial cultures were submitted for our cases.

A small case series describing castration in 8 Vietnamese potbellied boars reported no complications related to the surgical procedure (4). The overall complication rate in the current study was 5.7%, and the post-operative complication rate was 4.7%. This is similar to previous studies in dogs undergoing orchiectomy, which reported complication rates of 3.4% to 10.8% (13–15). Howe (15) further classified the complications in minor or major categories. All complications described in this report would be of the minor category, which was described as requiring little or no veterinary treatment/care and causing only a minimal increase in morbidity.

In the current report, the most common post-operative complication was mild peri-incisional swelling. Similar findings are observed in dogs, in which surgical incisional problems are the most frequently encountered complication and usually consist of mild incisional or scrotal swelling (15). Primary closure of the incisions is usually performed in that species (14,16). In equine studies in which primary closure is used, the reported rates of swelling can range from 1.9% to 5% (17,18). There was no association in our cases with the presence of complications and the use of primary or secondary intention healing of the incisions.

The only risk factor associated with development of post-operative complications was closure of the inguinal rings. All pet pigs experiencing complications had the inguinal rings closed, making it 6.6 times more likely to develop swelling. More tissue dissection and manipulation are necessary during surgery in order to close the inguinal rings. Additionally, an increased amount of suture material is present within the surgical site when the inguinal rings are closed. We hypothesize that the combination of those 2 factors could stimulate tissue inflammation and subsequent swelling. Closure of the inguinal ring has been recommended in pigs in order to prevent post-castration herniation; it has been reported that the rings might be larger in proportion to the size of the animal in pigs compared to other species (4). Inguinal ring closure was not performed in 38.6% of the cases herein and there were no complications reported in these patients. Our castrations were performed with a closed castration technique, which has been shown to reduce the rate of post-operative herniation in horses (19). Furthermore, herniation in commercial pigs is usually observed around 2 wk of age (5). The mean age at time of castration of our population was 6.3 mo, which is beyond the critical period for the condition. It is likely that most pigs predisposed to inguinal herniation would have shown some clinical signs by the time of castration, decreasing the likelihood of developing post-operative hernia in those patients which have not exhibited any indications of the condition before presentation. Based on this information, it can be suggested that closure of the inguinal ring is not necessary if a closed castration technique is employed, and that it might even lead to an increased rate of complications. One of the pigs which suffered from post-operative swelling initially presented for inguinal hernia. It cannot be excluded in that case that the initial condition and not the surgical technique itself predisposed to the post-operative swelling.

Ostevik et al (4) reported a complication rate of 25% (2/8 cases), which were all related to recovery from anesthesia and had no long-term implications (4). Our overall rate of anesthetic complications was 13.2%. In a recent study documenting the complications during anesthesia of 27 Vietnamese pot-bellied pigs, high incidences of hypoventilation (67%), hypotension (64%), and hypothermia (48%) were encountered (20). Only 5.6% of our cases developed hypotension compared to the 64% reported in the previous study. It might be interesting to compare anesthetic protocols for these populations; however, this was beyond the scope of this study.

Animal welfare is an important consideration when choosing a castration technique for pet pigs. It is now well-accepted that castration is a stressful and painful procedure, as indicated by a significant increase in blood adrenocorticotropic hormone, cortisol, and lactate following the procedure (21). In commercial pigs, castration is routinely performed between 2 and 14 d of age with minimal analgesia/anesthesia (5,22). This is believed to be inappropriate for older pigs (> 1 mo) and pet pigs, in which the procedure is usually performed under general anesthesia with associated pain management (5). We therefore recommend the use of NSAIDs while performing castration in pet pigs. All patients in the current study received multimodal analgesia during the procedure and in some cases after surgery as well. Further studies objectively measuring pain levels associated with the procedure and in relation to administration of different analgesics are warranted.

When administering extra-label antimicrobials for food producing animals, it is important to follow local and federal regulations. No regulations exist for antimicrobial use in farm animals defined as pets. In the United States and Canada, extra-label use of third-generation cephalosporins is allowed under a valid-client-patient relationship [Animal Medicinal Drug Use Clarification Act of 1994 and 21 CFR 530, the US Food and Drug Administration (FDA)]. Most of our pigs were treated with antimicrobials (96%; 54.4% third generation cephalosporins). However, in the current situation in which an increase in antimicrobial resistance is common, revision of our antibiotic therapy protocols should be performed. Considering that all our surgeries were performed in a sterile manner and in a hospital setting, and that castrations are considered clean procedures, the use of antimicrobials is questionable. It has been suggested that no antimicrobials are necessary for routine neutering of dogs and cats (23). Therefore, castrations in pet pigs might likewise not require administration of antimicrobials. This hypothesis should be further investigated.

Some of the limitations of the present study are inherent to its retrospective nature. Certain records were incomplete, and these missing data might have affected the results. The minimal number of complications affected the statistical power for this analysis and therefore only 1 risk factor could be identified. Additionally, no long-term follow-up was obtained for our cases. Information provided by 2 reports of orchiectomy in dogs showed that most complications were identified within the first 24 h after surgery, and that no additional complications were recognized at the 4- and 10-day re-evaluations (14,16). Based on these findings, we believe short-term follow-up times might not be detrimental to this study.

In conclusion, the pre-scrotal approach to descended testicles provides a safe, viable option for castration in pet pigs. The results from this retrospective case study demonstrate that this castration technique of pet pigs can be performed with a minimal rate of complications. It does not appear that age, weight, or closure of the incisions affects the complication rate. However, closure of the inguinal rings was associated with an increased rate of post-operative complications and these patients were 6.6 times more likely to suffer from peri-incisional swelling. Therefore, it is our recommendation that the inguinal rings not be routinely closed.