Reproduction in Miniature Pet Pig Females
For miniature pet pigs (MPPs), first estrus occurs as early as 3 months old in gilt piglets. The lack of estrus or the presence of 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 agent prostaglandin F2alpha, injected in two doses (8 mg and 5 mg in a 25-kg pig) 12 hours apart, can be administered when the corpora lutea have become susceptible to luteolysis after day 13 following estrus. Estrus should occur 3–7 days later.
Dystocia is of special concern in MPPs. Because the birth canal is too small to palpate for unborn pigs, radiographic or ultrasonographic evaluation may be indicated to determine whether there are 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 toxemic and has friable uterine tissue and vessels. There are several approaches to performing cesarean sections, 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, piglets born by cesarean section usually require hand-rearing.
The ideal time to perform ovariohysterectomy in MPPs is 4–6 months of age. Older female MPPs generally display irritable behavior for 2–3 days of estrus out of every 21 days of the estrous cycle. Due to the extensive vasculature in the broad ligaments of the horns of the uterus, ovariohysterectomy during estrus in older MPPs is a formidable task and is even more difficult if the pig is obese. Surgery should be delayed until ~7–10 days after estrus.
A distal midline approach, as with a cystotomy, is routinely used for ovariohysterectomy in MPPs. The uterine horns fold back and are located beside the body of the uterus with the ovaries. No ovarian ligament tearing, as in dogs and cats, is necessary. To prevent intermittent postsurgical hemorrhage from the vulva, when ligating the uterine stump, care should be taken to avoid penetrating the cervix with sutures. A right-flank approach may be used in extremely obese MPPs, in which wound dehiscence could be a complication.
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 the return of normal thermoregulation for 5–6 hours after anesthesia and should be used with caution.
Because some MPPs may become apneic when placed in prolonged dorsal recumbency, intubation is preferred over masking. However, MPPs may be difficult to intubate, and prolonged efforts at intubation may cause laryngeal edema and postsurgical complications. Spraying topical 2% lidocaine onto the larynx 2 minutes before attempting intubation can help. Especially small endotracheal tubes are typically required. A laryngoscope with an 8-inch blade is helpful.
Early spaying decreases the risk of ovarian cysts, uterine tumors, and cystic endometrial hyperplasia. The abdomen becomes obviously distended in cases of large ovarian or uterine masses (≥ 9.1–13.6 kg [20–30 pounds]). Vulvar hemorrhage may be a sign of a uterine tumor and can be life-threatening. Although most ovarian or uterine masses can be surgically removed, they can be extensive and invasive, resulting in death or requiring euthanasia, if not removed as soon as possible.
Reproduction in Miniature Pet Pig Males
MPP boars retained for breeding should be kept in secure pens; because of their unpredictable behavior around other animals or people, boars should not be kept as pets. Neutering is usually performed at 8–12 weeks old. Determining whether both testicles are descended before surgery is important because cryptorchidism occurs in MPPs. An inguinal hernia is another possible complicating factor.
A miniature pig with a left inguinal hernia. Note the unilateral swelling in the inguinal area.
Courtesy of Dr. Bruce Lawhorn.
The preputial diverticulum after it has been fully everted in a miniature pig.
Courtesy of M. C. Tynes.
The preputial diverticulum is clamped at the base in preparation for removal of the diverticulum in a miniature pig. A continuous suture is then placed encompassing the base and the forceps. The forceps are removed and the suture tightened. After the suture is tied off, the stump is released back into the prepuce.
Courtesy of M. C. Tynes.
A miniature pig with a left inguinal hernia. Note the unilateral swelling in the inguinal area.
Courtesy of Dr. Bruce Lawhorn.
The preputial diverticulum after it has been fully everted in a miniature pig.
Courtesy of M. C. Tynes.
The preputial diverticulum is clamped at the base in preparation for removal of the diverticulum in a miniature pig. A continuous suture is then placed encompassing the base and the forceps. The forceps are removed and the suture tightened. After the suture is tied off, the stump is released back into the prepuce.
Courtesy of M. C. Tynes.
The midline skin incision is made cranial to the scrotum, and structures such as the vas deferens and blood vessels are ligated and excised in a way that is similar to the procedure in dogs. Inguinal hernias are common in miniature pigs, and both inguinal rings should be closed at castration to prevent herniation. Removal of the tunic, cremaster muscle, and extraneous subcutaneous tissue, followed by closure to obliterate empty space, helps to prevent seroma formation.
Chemical Restraint for Miniature Pigs
Agent | Dosage | Comments |
|---|---|---|
Atropine | 0.02–0.05 mg/kg, SC, IM, or IV | Anesthesia adjunct for increasing heart rate and decreasing GI and respiratory secretions |
Isoflurane or sevoflurane | 4%–5% for anesthetic induction or to effect, and 1%–3% for maintenance | Especially for pigs < 8 wk old or for sick or debilitated patients |
Dexmedetomidine (DE), midazolam (MI), and butorphanol (B) | 0.01–0.04 mg/kg DE + 0.1–0.3 mg/kg MI + 0.2–0.4 mg/kg B; all IM | Smooth induction and recovery; can reverse if needed |
Ketamine (K), xylazine (X), and butorphanol (B) | 5–10 mg/kg K + 2 mg/kg X + 0.22 mg/kg B; all IM | Butorphanol enhances analgesia |
At the time of castration, the preputial diverticulum (scent gland) may be removed by eversion and excision to minimize the pooling and discharge of foul-smelling preputial fluid. Umbilical hernias may complicate removal. Early castration interferes with the development of the preputial diverticulum, making its removal less critical, especially in MPPs kept outside.
Malignant hyperthermia has been reported rarely in MPPs under isoflurane anesthesia, so it is thought to be rare in MPPs.
Enforcing food withholding for 24 hours and withholding water for 4–6 hours before sedation or anesthesia is recommended.
