Reproductive surgical sterilization in waterfowl has several potential uses but has rarely been attempted in zoological medicine. Laparoscopic surgery in wildlife species provides several benefits as compared to conventional surgery including less postoperative pain, faster healing times, and the ability to return the patient back to its environment more rapidly after the procedure. This project describes several surgical techniques that were developed and evaluated to perform orchidectomies and ovariectomies in mallard ducks (Anas platyrhynchos).
Population control of captive wildlife is an important management tool in zoological institutions. Historically, methods of contraception in avian species have been limited. The goal of our project has been to investigate safe and effective methods of surgical sterilization in waterfowl. At our institution, non-migratory mallard ducks are present in very high numbers and commonly brought to our hospital as orphaned ducklings, or with medical problems. In partnership with the Florida Fish and Wildlife Conservation Commission (FFWCC), and under jurisdiction of the United State Fish and Wildlife Service (USFWS), Disney’s Animal Programs has been surgically sterilizing mallard ducks for the last year.
Although castration (a.k.a. caponization or orchidectomy) has been routinely performed in young male poultry for many years, castration of other avian species in zoos is rarely done and has been associated with surgical complications including hemorrhage, and organ regeneration. Sterilization in female birds has usually been limited to salpingohysterectomy in pet avian species. In some avian species it is believed that removal of the uterus (shell gland) provides a feedback mechanism to the ovary, which limits follicular growth. However, in waterfowl, continued yolk release from the ovary after salpingohysterectomy may lead to yolk-related peritonitis.
Over the last year, approximately 200 mallard ducks were surgically sterilized. This number includes both juvenile and adult, and male and female birds. We evaluated several surgical approaches and techniques during this time. This paper describes some of the possible complications associated with each technique and describes our current method of choice for waterfowl sterilization.
Birds are given an injection of leuprolide acetate (Lupron Depot®, TAP Pharmaceuticals Inc., Lake Forest, IL, USA), at 1 mg/kg IM from 7–14 days prior to surgery. For surgery, animals are placed under general anesthesia and intubated. The birds are placed in right lateral recumbency, feathers are plucked, and a surgical preparation is done from the 6th rib caudally to the pubis. In adult males, a bilateral approach is required for castration. In juvenile ducks, the sterilization can be done via two small laparoscopic incisions utilizing 3–5 mm cannulas. In mature adults, the more cranial incision will need to be large enough to place surgical clips and remove the gonad. The first incision is made just cranial and parallel to the femur. The underlying muscle bellies are bluntly separated using a hemostat, which is then utilized to penetrate into the coelomic space. The laparoscope is inserted into this incision, and the tip can be used to place a hole in the underlying air sac. A 6 mm incision is now made behind the caudal musculature of the femur (iliotibialis) and a straight blunt forcep is introduced in a craniodorsal direction until it can be visualized in the coelom via the laparoscope. A 3–5 mm cannula is then placed in this location for laparoscopic instrument use.
The following methods of hemostasis and gonad resection were evaluated: radiosurgery, harmonic scalpel, hemoclip application, carbon dioxide laser, Ligasure™ (Valleylab, Boulder, CO, USA) unit coagulation, and segmental tissue resection followed by cryosurgery of remaining gonadal tissue.
Initially, our greatest surgical concern was hemostasis, and thus radiosurgery, the harmonic scalpel, and the Ligasure™ coagulation system were all utilized. Although these techniques did aid in hemostasis, we found that each one of these hemostasis techniques was associated with cardiac arrhythmias (severe tachycardia) and sometimes death. It is hypothesized that these methods induce some degree of collateral stimulation/irritation to the closely adjacent adrenal gland. It is believed that this stimulation of the adrenal gland may initiate catecholamine release, which in turn, causes cardiac arrhythmias and sometimes cardiac arrest. Initially, this theory was difficult to prove, but various degrees of tachycardia were observed repeatedly when any of these electrical systems were utilized adjacent to the adrenal gland. For this reason, these methods of gonad resection were discontinued.
In juvenile ducks, the current method of choice has been to utilize a 3 mm cupped laparoscopic biopsy instrument to remove the gonad piecemeal. This is done by grasping at the caudal pole of the gonad with the instrument and then gently rotating the piece of tissue continuously while withdrawing the instrument. This technique allows gentle traction and resection of that piece of the gonad. It is important to not use the biopsy forcep to cut through the tissue, but rather as a holding device for twisting. It is critical that the entire biopsy forceps be visualized, and that the vena cava or other major vessels not be compromised during this procedure. Immature males will require 3–6 extractions to remove all the tissue, and females may require 10–20 extractions depending on the size of the ovary and size of the pieces taken.
In general, the testis is well delineated and not as directly attached to the vena cava and adrenal gland. For this reason, it is much easier to perform a castration, and there is less chance of leaving any gonadal tissue, which can regenerate. The ovary is much more closely associated with the adrenal gland and vena cava. In immature male ducks, both testes can often be visualized and safely removed from the left incision. A hole will need to be placed in the right abdominal air sac for visualization. If the testes cannot be fully visualized, it is better to close the left side and perform a bilateral approach.
The same technique of piecemeal gonadal tissue resection is utilized with the females. Our preliminary work showed that in several cases, it was impossible to see or safely remove all the ovarian tissue and that gonad regeneration was then a possible complication. For this reason, we currently utilize cryosurgical techniques after ovariectomy to devitalize any remaining tissue. A 3 mm insulated copper probe is placed into a dewar flask of liquid nitrogen. The frozen tip of the probe is then inserted through the instrument port and used to devitalize the remaining ovarian tissue. The tip is placed over the adrenal and vena cava sites for 2–3 seconds in three separate freezing rotations. It is important to avoid causing necrosis of adrenal tissue or the vena cava. Preliminary studies have indicated this technique helps reduce the incidence of gonadal regrowth. We are currently involved in a study that will document the long-term efficacy of this technique.
Carbon dioxide laser surgery with a laparoscopic tip was also evaluated for efficacy. It was found that although this may be effective, it is difficult to safely direct the laser beam laparoscopically once inside the patient, and that inadvertent application to the vena cava or adrenal gland can lead to significant hemorrhage. Other forms of laser (e.g., diode laser) may be easier to precisely aim and may be useful in the future.
In mature male ducks, hemostasis cannot be accomplished with the previously described techniques and hemoclips must be utilized. Laparoscopic 5 mm clip appliers can be used, or a larger incision can be made and a 90° hemoclip applier can be utilized. Typically, two clips are applied at the very base of the testes, ensuring that the vena cava and adrenal are not entrapped. Once the clips are in place a laparoscopic scissor is placed in the instrument port and the testes resected and removed. A bilateral approach is needed for an adult duck castration.
Closure is typically done in two layers, with the first incorporating the celomic serosa and associated muscles, and the second layer including subcutaneous tissue and skin.
Patients receive butorphanol (Torbutol™, Fort-Dodge, IA, USA) 2 mg/kg IM during their surgery for postoperative analgesia and meloxicam, (Metacam, Boehringer-Ingelheim, Vetmedica Inc., St. Joseph, MO, USA) 0.1 mg/kg PO for two additional days after surgery. Incisions are evaluated at 4–7 days post-surgery and if the animal is doing well, it is fitted with a USFWS band and released back to the wild.
Results and Discussion
Although there is some question about the use of leuprolide acetate in hormone regulation in waterfowl, this drug is given to help decrease the vascular supply to the gonads. A controlled study to evaluate its efficacy in waterfowl was not done. In poultry, keeping the birds in complete darkness for an extended period of time is commonly practiced prior to caponization, and is believed to decrease the blood supply to the gonads.
Initially, hemorrhage was our biggest concern, but with careful manipulation in juveniles and the use of hemoclips in adults, hemorrhage was not a significant problem. In those cases where local hemorrhage occurred, hemostatic absorbable gelatin sponge foam (Gelfoam™, Upjohn Company, Kalamazoo, MI, USA) and direct pressure were utilized to aid in stasis.
Cardiac arrhythmias were only seen when electronic devices were used in proximity to the adrenal gland. This was true in both male and female birds. Several drugs in mammals can be used to block catecholamine-induced arrhythmias, and their use was discussed, but not attempted. It is interesting to note that direct manipulation of the adrenal and collateral cryofreezing from the ovary were very rarely seen to induce arrhythmias.
It is our goal to be able to provide a safe, effective sterilization tool for zoo and wildlife professionals who work with avian species. Laparoscopy provided several advantages in this procedure, including small incisions, less postoperative pain, faster healing, and less recuperative time before return to the wild. Laparoscopy also allows magnification of the surgical area of interest and is particularly important in juvenile animals with small gonads to ensure complete resection. In addition, laparoscopy allows excellent visualization in deep holes and facilitates the ability to perform a castration procedure from a single left-sided approach.
When we first began performing these surgeries, each procedure took well over 60–90 minutes. Currently, both male and female birds can be sterilized in 15–25 minutes.
I am indebted to the following individuals, whose support has helped make this such a successful project: Leanne Blinco, Lidia Castro, Greg Fleming, Deidre Fontenot, Lori Grady, P.K. Robbins, the hospital interns and all of the hospital staff at Disney’s Animal Programs. I would also like to thank Diane Eggeman and her colleagues at the Florida Fish and Wildlife Conservation Commission for their partnership through the years.