Reproduction of Potbellied Pigs
First estrus occurs as early as 3 mo of age in gilt piglets. The lack of estrus or a distended abdomen in a young gilt may be due to pregnancy if she has been exposed to littermate boars. If the female does not cycle, the abortifacient prostaglandin F2α , given as two injections (8 mg and 5 mg in a 25-kg pig) 12 hr apart, can be administered when corpora lutea have become susceptible to luteolysis after day 13 after estrus. Estrus should occur 3–7 days later.
Dystocia is of special concern in PBPs. Because the birth canal is too small to inspect for unborn pigs via palpation, radiography or ultrasonography may be indicated to reveal undelivered piglets. Oxytocin (5–10 U) may be used to aid delivery if the vaginal canal is patent. The decision to perform a cesarean section, if indicated, should be made promptly, before the sow becomes toxic and has friable uterine tissue and vessels. Cesarean section may be performed by several approaches, but the right flank approach has two advantages: the piglets nurse away from the incision, and gravity pulls the incision shut, minimizing the chance of dehiscence. Regardless of surgical approach, surviving piglets will probably require hand-raising.
Ovariohysterectomy in PBPs at 4–6 mo of age is ideal. Older female PBPs generally display irritable behavior for 2–3 days of estrus out of every 21 days of the estrous cycle. Performing an ovariohysterectomy during estrus in older PBPs is a formidable task because of the tremendous vasculature in the broad ligaments of the horns of the uterus; surgery should be delayed until ~7–10 days after estrus. A distal midline approach, as if performing a cystotomy, is routinely used for ovariohysterectomy. The uterine horns fold back and are located beside the body of the uterus with the ovaries. No ovarian ligament tearing is necessary as in dogs and cats. Penetration of the cervix by sutures should be avoided when ligating the uterine stump to prevent intermittent postsurgical hemorrhage from the vulva. A right flank approach may be used in extremely obese PBPs, in which wound dehiscence could be a complication. Isoflurane or sevoflurane anesthesia provides excellent muscle relaxation. (Malignant hyperthermia [see Malignant Hyperthermia] has been reported only once in a PBP under isoflurane gas anesthesia, so it is thought to be rare in PBPs.) Hypothermia during and after surgery is an important concern. A baseline rectal temperature should be recorded at anesthesia induction, and normal body temperature should be maintained until recovery is complete. Injectable anesthetics such as xylazine plus tiletamine-zolazepam can delay normal thermoregulation for 5–6 hr after anesthesia. Because some PBPs may become apneic when placed in prolonged dorsal recumbency, intubation is preferred to masking; however, PBPs may be difficult to intubate, and prolonged efforts at intubation may cause laryngeal edema and postsurgical complications.
Early spaying also reduces the risk of ovarian cysts, uterine tumors, and cystic endometrial hyperplasia. An obviously distended abdomen is seen with large ovarian or uterine masses (≥20–30 lb). Vulvar hemorrhage may be a sign of uterine tumor and can be life-threatening. Although most ovarian or uterine masses can be surgically removed, some are so extensive and invasive that euthanasia is required.
PBP boars retained for breeding should be kept in secure pens; they should not be kept as pets because of the unpredictable behavior of boars around other animals or people. Neutering is usually performed at 8–12 wk of age, using injectable or gas anesthesia. One protocol for injectable anesthesia is xylazine at 2.2 mg/kg, IM, followed by tiletamine-zolazepam at 6.6 mg/kg, IM, both injections in the hams. Determining whether both testicles are descended before surgery is important because cryptorchidism is seen in PBPs. An inguinal hernia is another possible complicating factor. The midline skin incision is made cranial to the scrotum, and structures such as the vas deferens and blood vessels are ligated and excised similar to the procedure in dogs. Both inguinal ring areas should be closed to prevent herniation. Removal of tunic, cremaster muscle, and extraneous subcutaneous tissue, followed by closure to obliterate empty space, help prevent seroma formation. At the time of castration, the preputial diverticulum or “scent gland” may be removed by eversion and excision to minimize the pooling and discharge of foul-smelling preputial fluid. Umbilical hernia may complicate removal. Early castration may interfere with the development of the preputial diverticulum, making its removal unnecessary, especially in PBPs kept outside. Tetanus antitoxin (if no current tetanus toxoid vaccination) and antibacterial injection are given after surgery of the reproductive tract.