Neutering companion exotic mammals (Proceedings)

One of the main reasons for neutering exotic pet mammals is to control reproduction. Medical and behavioral indications are also important factors to consider in making a decision to have a pet neutered. In most species, castration makes male mammals less aggressive both to other animals and to their owners. The urine of many intact male mammals has a more potent odor and is used for territorial marking. The odor and behavior can often be modified by neutering. In many species, mammary neoplasia is influenced by the presence of hormones and ovariectomy can decrease the occurrence of mammary cancer. Ovarian and uterine diseases are effectively prevented by either ovariectomy or ovariohysterectomy.

Basic Principle

When neutering a mammal the goal is to remove the gonads which are responsible for hormone production. It is not necessary to pull the testicle out, far from the body risking accidentally tearing the vessels. The surgeon only needs the entire testicle exposed so the vessels can be ligated. Once transected (or torn) the vascular pedicle retracts into the retroperitoneal space as the testicular vessels are branches off the renal vessels. Hemorrhage from these vessels, therefore, occurs in the retroperitoneal space and does not cause hemoabdomen.

In species with a distinct scrotum, the scrotal skin is usually thinner and more delicate than the inguinal or the prescrotal skin. Therefore, I prefer to make the incision in the thicker inguinal or prescrotal skin if possible. It seems to bother the patient less and I believe they are less likely to bother their incision.

Closed castration describes removing the testicles along with the tunics without making an incision into the tunics. Open castration describes making an incision into the tunic (open) and removing the testicle, vas deferens, and associated vessels but leaving the incised tunic. In general, the testicles are easier to exteriorize using an open technique as the only attachment to other tissues is at the epididymis. With a closed castration, the external surface of the tunic is attached to the surrounding tissues. All of these attachments must be broken down to exteriorize the testicle. The main advantage to a closed technique is that it ligates the tunic near the inguinal canal minimizing the potential for an inguinal hernia to develop.

In the USA, ovariohysterectomy is generally recommended over ovariectomy alone. Investigations comparing ovariectomy to ovariohysterectomy support that removal of the ovaries but not the uterus is associated with no risk of uterine disease. Ovariectomy should be considered an effective alternative to ovariohysterectomy. It is not necessary to risk tearing the ovarian vessels in an effort to exteriorize the ovary far from the abdominal cavity. You only need to expose the vessels enough to effectively ligate them.

Ferret Ovariohysterectomy

Ovulation is induced at breeding in ferrets. Unbred females remain in estrus until they are stimulated to ovulate by breeding or artificial means. A female ferret may remain in estrus for 6 months or more during which time the body's estrogen levels remain high. This chronic hyperestrogenemia can result in bone marrow suppression and, potentially, fatal aplastic anemia. Ovariohysterectomy should be performed as soon as the patient is stable. Blood transfusions are indicated in ferrets with a PCV < 30%.

Prevention by spaying females at 4-6 months of age or within the first two weeks of the first estrus is the best action. In the USA most ferrets are spay at an early age (5-6 wk) prior to arrival at pet stores. A CBC and platelet count should be evaluated on all intact female ferrets prior to ovariohysterectomy. Performing ovariohysterectomy in ferrets is analogous to that in cats with the ventral midline incision centered midway between the umbilicus and pubis. The uterus is bicornuate and the suspensory ligaments are loose and easily stretched or broken.

Spayed female ferrets that show clinical signs of estrus are usually affected with adrenal neoplasia or, rarely, have residual ovarian tissue. Female ferrets that have been spayed but that have residual ovarian tissue will generally present with vulvar swelling and signs of estrus at an earlier age (< 2 yrs age) than ferrets with adrenal tumors (> 2 yrs age). In most ferrets with ovarian tissue, vulvar swelling subsides following the administration of 100 IU of human chorionic gonadotropin, while in ferrets with adrenal disease this hormone has no effect. Though ectopic ovarian tissue has been reported in ferrets, in most cases residual tissue is a result of incomplete ovariectomy.

Ferret Castration and Vasectomy

Most pet ferrets are descented (anal sacculectomy) and castrated at 5-6 wks age at the breeding facility. Intact male ferrets are larger, more heavily muscled, and have a more pungent odor than castrated males. Castration will effectively alter behavior, physical characteristics, and the odor. Because of the problems with breeding females in estrus potentially developing fatal aplastic anemia, vasectomized males are used in breeding facilities to induce ovulation.

The gross male anatomy of ferrets is more similar to that of dogs than of cats; however, most surgeons castrate ferrets using scrotal incisions and techniques similar to those used in cats, not dogs. While complications with scrotal incisions are not reported, the prescrotal skin is thicker and less fragile, and potentially less sensitive than that of the scrotal skin. Both techniques are acceptable and an open technique or a closed technique can be employed – there is no evidence that one method is better.

A vasectomy is best performed through an inguinal skin incision on each side of the prepuce. The spermatic cord is generally palpable and the incision is made directly over the cord. Use blunt dissection to identify the spermatic cord and isolate it within its vaginal tunic. Make a 3-5 mm incision in the vaginal tunic. Be careful not to cut the vascular bundle. Separate the vas deferens from the vascular bundle using blunt dissection. Using hemostatic clips or ligatures of monofilament suture, place two sutures roughly 1 cm apart. Cut the segment of vas deferens out from between the ligatures. Suture the incision in the tunic closed using 4-0 or 5-0 monofilament absorbable material leaving one end of the vas outside the tunic. This will help prevent the rare complication of recanalization of the vas. It is recommended that the ferret not be used for breeding for 6 weeks to allow the sperm within the vas to die.

Rabbit Ovariohysterectomy

Indications for ovariohysterectomy in rabbits include control of reproduction and uterine adenocarcinoma. There is a high incidence of uterine adenocarcinoma in rabbits over the age of 5 years. The uterus of young rabbits is found just dorsal to the bladder, coiled in the caudal abdomen. In older rabbits, the cervices are dorsal to the bladder, but the horns extend laterally. The uterus and ovaries are generally easy to exteriorize; however, they are more fragile than those of dogs and cats. The uterus is bicornuate and each horn has its own cervix. There is no distinct uterine body. The mesometrium of rabbits is a site of fat storage which can make surgery more challenging as it is often difficult to identify the vessels.

A 2-3 cm incision is made starting midway between the umbilicus and pubis extending caudally. The cecum and bladder may be directly under the linea alba so be careful entering the abdomen. Once the peritoneal cavity is opened the viscera will drop away as air enters the peritoneal cavity. The uterus is usually visible dorsal to (under) the cranial pole of the bladder. One uterine horn may be lifted through the incision using atraumatic forceps. Once the uterine horn has been elevated through the incision it is traced to the ovary which is loosely attached to the dorsal body wall by a long, fat-filled mesovarium. The oviduct is usually visualized as a fine tubular structure which literally encircles the ovary. The ovarian ligament does not usually need to be broken down. There are many vessels that supply the ovary within the fat of the mesovarium. An opening is created by blunt dissection through the fat of the mesovarium and a ligature is passed around the portion of the mesovarium containing the vessels supplying the ovary. As the suture is tightened it will cut through the fat, but will ligate the blood vessels. This procedure is repeated on the contralateral side and the fat-filled broad ligament of the uterus may be broken down by gentle blunt dissection. The uterus may be ligated on either the cranial or the caudal side of the cervices but most recommend caudal. The uterine vessels lay on each side of the uterus several millimeters lateral to the uterus. It is best to ligate these vessels individually and place a transfixation ligature around the vagina vault prior to transection. Closure is routine.

Rabbit Castration

Indications for castration in rabbits include decreasing the odor of the urine, marking behavior, and aggression and territoriality. The testes of rabbits move freely between the abdomen and the scrotum through the function of a well developed cremaster muscle. The inguinal canal is open in rabbits; however, the intestine does not herniate because of the large epididymal fat pad which fills the inguinal canal when the testes are within the scrotum and the inguinal fat pads within the abdomen. The ligament of the tail of the epididymis which attaches the tunica vaginalis to the scrotum is quite strong in rabbits.

There are 3 methods commonly recommended for castration of rabbits: closed, open with closure of the inguinal ring, and open with preservation of the epididymal fat pad. The initial incision may be scrotal, inguinal or prescrotal. A prescrotal incision allows the surgeon to remove both testicles through one incision but is technically more difficult. For a scrotal incision, a 1-1.5 cm incision is made through the scrotum longitudinally on each side about midway along the length of the scrotum. The tunic is grasped and the testicle is removed from the scrotum with the tunic intact. The tunic is adhered to the scrotal fascia and to the tip of the scrotum. The attachments must be broken down to allow exteriorization of the testicle. Caudal traction is applied to the testicle and dry gauze is used to strip the facial attachments allowing the narrow portion of the cord to be exteriorized. Once the testicle has been exteriorized adequately the cord is ligated. The same closed technique can also be used with inguinal incisions. The skin is thicker more proximally but more dissection is needed to free up the tunic.

For an open castration with closure of the inguinal ring, the incision is made as described above and the vaginal tunic is incised to allow exteriorization of the testicle and spermatic cord. The tail of the epididymis will still be attached to the tunic. This attachment must be broken down freeing the testicle for removal. The spermatic cord is double ligated and the testicle is removed. The vascular pedicle is traced craniad and the inguinal canal is identified. A single interrupted suture is placed across the inguinal canal. Another technique is to perform an open castration being careful to remove only the testicle and leaving the epididymal fat intact. The fat will prevent herniation of intestine. With any technique the incisions can be left open to heal by second intention or sutured closed using either an intradermal pattern, tissue adhesive, or skin staples.

Rodents

There are three basic groups of rodents – myomorph (mouse-like), sciurimorph (squirrel-like) and hystrichomorph (guinea pig-like). Anatomically, the hystrichomorphs (which includes guinea pigs and chinchillas) are unique. The males do not have a distinct scrotum and the testicles are located in the inguinal region on each side of the penis.

Ovariohysterectomy

Indications for ovariohysterectomy in rodents include control of reproduction, dystocia, pyometra, ovarian disease such as cystic ovaries, and, potentially, behavior alteration. The ovaries are located at the caudal pole of the kidneys within a rather large fat pad. There is a single artery and vein which run medial to the ovaries and extend along the uterus following the uterine horns to the uterine body. Rodents do have a uterine body and a single cervix.

The patient is placed in dorsal recumbency and prepared for aseptic surgery. Be careful not to damage the urinary bladder and cecum directly under the body wall. The uterine horns are identified dorsal to the apex of the bladder and followed cranially to the ovary. The oviduct circles cranially around the ovary. It is recommended that the uterus be ligated cranial to the cervix in order to prevent urine leakage from the transected vagina. Closure is routine.

In small rodents, it is possible to remove the ovaries without removing the uterus through a lumbar approach. The patient is placed in ventral recumbency and the lumbar and flank areas are clipped and prepared for aseptic surgery. A single dorsal midline incision may be made and the skin shifted from one side to the other to gain access to each ovary or, alternatively, a transverse incision can be made on each side. Blunt dissection is used caudal to the last rib at approximately the level of the third lumbar vertebra through the muscles of the body wall into the peritoneal cavity. The ovary is located within the fat at the caudal pole of the kidney and it is carefully exteriorized. A hemostatic clip or ligature is placed on each ovarian pedicle prior to transection. The muscle is apposed and the skin is closed in a routine manner.

Orchidectomy

Castration is used to control reproduction in the pet rodent. It is easier to perform than ovariohysterectomy and is associated with less morbidity. It may also be indicated to stop urine marking behaviors, decrease aggression, and for medical reasons such as tumors. The testicles of the rodents are relatively large in comparison to body size and descend in the first week or two of life. The inguinal canals remain open and a functional cremaster muscle allows the testicle to migrate into and out of the abdominal cavity. As described in rabbits, rodents also have a large epididymal fat pad which prevents intestinal herniation. The large seminal vesicles also partially occlude the internal inguinal ring preventing herniation.

Guinea pigs and chinchillas do not have a distinct scrotum and the testicles are on each side adjacent to the penis. Some surgeons feel that guinea pigs are more likely to herniate the seminal vesicles through the inguinal ring and recommend closure of the inguinal ring to prevent this. These hystrichomorph rodents also seem to be more prone to the development of incisional infections than other species. The reason for this is undetermined. To try to minimize the risk of infection, proper aseptic technique, gentle tissue handling, and the use of perioperative antibiotics are recommended. Because of the location of the incisions, it is feasible that the incision is dragged along a dirty substrate, soaked in urine and contaminated with food and feces. Therefore, the owners must pay close attention to hygiene cleaning the substrate frequently until the incisions have healed. Most of these (unlike other abscesses in rodents) respond to local debridement and systemic antibiotics.

In other rodents, following routine preparation of the scrotum a single, transverse 1 cm incision is made at the distal (caudal) tip of the scrotum. The incision is extended through the tunic on each side of midline to allow exteriorization of each testicle. The tail of the epididymis is pried away from the scrotal skin. Caudal retraction is applied exposing the spermatic cord. The cord is ligated and the testicle is transected distal to the ligatures. The tunic may be closed using a 4-0 to 6-0 synthetic, absorbable material. The skin incision may be left open to heal by second intention or may be closed using a tissue adhesive.

Sugar Gliders and Other Marsupials

Marsupials have unique genitalia presenting challenges during spay and castration. Sugar gliders are notorious for self-traumatizing incisions and wounds. In male gliders, the scrotum is pendulous and located cranial to the vent. The penis is bifurcated and located within the cloaca so it is not externally visible. Female gliders have their pouch which is best avoided during skin incision and lateral vaginae which can be confused with the uterus adding a challenge to ovariohysterectomy. There are two separate uterine horns and no uterine body. The lateral vaginae are quite long and convoluted while the uterine horns are shorter and linear. There is a short median vaginal cul-de-sac.

Castration

Two techniques are commonly used to castrate sugar glides, scrotal ablation and scrotal incision. Because of their tendency to self trauma, many prefer scrotal ablation to eliminate the scrotum as a structure to be damaged. Still, some gliders will open the base of the scrotum and chew into body wall. Some surgeons have concern about the pendulous scrotum collecting blood in the short term or getting caught on things long term if only the testicles are removed in a more traditional manner; however, the scrotum will atrophy.

For scrotal ablation, a circumferential incision is made around the base of the scrotum and the spermatic cords are exposed. They are each ligated prior to being transected. The remainder of the attachments between the scrotum and the body wall are severed and the skin defect closed in an intradermal pattern.

In a more traditional approach to castration, two scrotal incisions are made, similar to performing a castration in a cat. The spermatic cords are ligated and the incisions closed with a single intradermal stitch. The goal is to not have anything exposed that will attract the animal's attention. Sedation may be helpful.

A technique using a carbon dioxide laser appears to result in less risk of self trauma. The laser will seal nerves resulting in less pain and irritation which appears to decrease their attraction to the site. The laser is used to do a scrotal ablation. It will cut through the skin as well as the spermatic cords within seconds. No sutures are used to minimize attraction to the site. Radio frequency electrosurgery also appears to be effective.

Ovariohysterectomy

A paramedian skin incision is made along the lateral aspect of the pouch. The skin is shifted to expose the midline for a midline celiotomy. The reproductive tract is exposed by exteriorizing the urinary bladder. The ovaries are red and granular in appearance. They lay along the medioventral side of the uterus on each side. The ovarian vessels are ligated and the uterine horns exposed to the level of the median vaginal cul-de-sac. The horns are each ligated at the cul-de-sac cranial to the lateral vaginae. The body wall and skin are closed routinely. It is best to place an intradermal pattern in the skin being very gentle.