Marsupialia (Marsupials)


Chapter 33

Marsupialia (Marsupials)



Larry Vogelnest



General Biology


Marsupials are an ancient and diverse mammal group, inhabiting a wide range of environments, from high alpine regions to coastal forests and deserts. Many species are arboreal, others are both arboreal and terrestrial, some completely terrestrial, and a few fossorial, and one species, the water opossum (Chironectes minimus), is aquatic. Many are nocturnal and some are diurnal or crepuscular. They range in body size from as small as 4 grams (g) up to 85 kilograms (kg). Many species do not live much beyond 10 years. Males of some dasyurids all die in the wild after their first year. A few such as wombats may live up to 30 years.


Numerous defining features of marsupials distinguish them from other mammals: the anatomy of the female reproductive tract; the very short gestation period, with young born in an embryonic state; and a lengthy lactation period, during which the young remain in the pouch. The derivation of the term marsupial from “marsupium” and the implication that all female marsupials have a pouch is not correct. The distinction of marsupials from eutherian mammals as not having a placenta is also not correct.


The extant marsupial species are restricted to Australasia and the Americas, with the majority of the 333 species occurring in Australia, New Guinea, and nearby islands. The subclass Marsupialia is divided into seven orders: Didelphimorphia (opossums, 92 spp.), Paucituberculata (shrew opossums, 6 spp.), Microbiotheria (Monito del Monte [Dromiciops gliroides]), Dasyuromorphia (dasyurids, 71 spp.), Peramelemorphia (bandicoots and bilby [Macrotis lagotis], 21 spp.), Notoryctemorphia (marsupial moles, 2 spp.) and Diprotodontia (koala [Phascolarctos cinereus], wombats, possums, gliders, macropods, 140 spp.).73



Unique Anatomy and Physiology67,71,73


Musculoskeletal System


An ossified patella does not exist except in bandicoots and the bilby. Epipubic bones extend from the cranial aspect of the pubis. Paired clavicles are present in all species except in bandicoots and the bilby. Other than in opossums, dasyurids and the numbat (Myrmecobius fasciatus), the second and third digits of the hindfoot are syndactylus.


In macropods, the atlanto-occipital articulation is highly flexible, allowing the muzzle to remain horizontal, whether the neck is horizontal or vertical. This may be associated with some weakness at this articulation, possibly accounting for the high incidence of traumatic fractures at this site. The mandibular symphysis of kangaroos and wallabies is unfused and flexible, whereas in the banded hare-wallaby (Lagostrophus fasciatus), bettongs, and potoroos, it is fused.




Gastrointestinal System


Macropods are foregut fermenters. In a process known as merycism, macropods, particularly the browsers and grazers, occasionally regurgitate food into their mouths, which involves a rather violent heaving motion with vigorous movements of the forelimbs and the thorax. The bolus is not generally rechewed as in ruminants and is quickly reswallowed.14 Koalas, wombats, and most possums and gliders are monogastric, hindgut fermenters. Koalas possess the largest cecum relative to body size among all known mammals. The wombat small intestine is short; the colon is large and sacculated; and the cecum is vestigial. In possums and gliders, an expanded cecum is the main site for fermentation in most species. The intestines of the striped possum (Dactylopsila trivirgata) and honey possum (Tarsipes rostratus) are simple because of the lack of plant material in their diet. Coprophagy of cecal contents occurs in some species of ringtail possums. Dasyurids, bandicoots, and the bilby have simple gastrointestinal tracts.


In females, the urogenital sinus (into which the urethra discharges), together with the rectum, opens into the common vestibule (or cloaca). In males, the penis lies within the common vestibule. The urogenital openings are ventral to the rectum.



Skin


Many species of dasyurids, opossums, and the numbat lack a pouch. Some species develop a temporary pouch from folds of skin on either side of the abdominal teats during lactation. Male marsupials lack teats. Numbers of teats in females varies: 2 in koala, wombats, 4 in macropods, numbat, 4 to 12 in dasyurids, 2 to 6 in possums and gliders, 6 to 8 in bandicoots, bilby, and 4 to 13 in opossums. Marsupials are well endowed with cutaneous glands, which have various functions. Macropods generally have thin skin, particularly in the inner surfaces of the limbs, and is particularly pronounced in the forelimbs, where the vascularity of the subcutis is significantly increased. Wombat skin is considerably thicker than that in other marsupials and quite inelastic, and all three species have a characteristic “sacral plate” on the rump, almost as rigid as bone. Gliders are distinguished from possums by the presence of a gliding membrane extending from the hindlimb to the forelimb.



Sensory Systems


Macropods have a wide field of peripheral vision enabling them to see movement in almost every direction, and binocular vision enables them to have more precise close vision. They have good day and night vision. Despite this, they appear to have difficulty navigating obstacles and barriers that are not solid, especially when alarmed and fleeing. The iris is thick and uniformly brown, and the pupil is circular and may be dilated easily with tropicamide. The fundus is heavily pigmented (usually dark brown) ventrally, whereas dorsally it is usually lighter in color, and in some animals, the choroidal blood vessels may be seen through the pigment. The optic disk sits at the junction between these two zones and is well vascularized. Retinal vessels are not prominent. All macropods have persistent hyaloid vessels (seen as a tuft of vessels arising from the center of the optic disk and extending anteriorly toward the posterior lens capsule). In most macropods, they are fixed anteriorly and are not easily visualized. If not fixed, they may be seen moving within the vitreous. In many kangaroos, myelination of the nerve fiber layer may be seen extending from around the optic disk. This myelination is generally most obvious in the lateral and medial aspects.62


The koala has relatively small, spherical, frontally placed eyes. The cornea occupies a relatively large segment of the globe. A tapetum extends across the retina above the optic disk, and, as in many other marsupials, the retina is essentially avascular except for a small area on the optic disc itself.56 Mean intraocular pressure is 24.2 ± 6 mm Hg.26 The iris is usually brown. The pupil is a vertically orientated slit. The lacrimal puncta are slitlike openings just inside the lid edges, 2 to 3 millimeters (mm) from the medial canthus. Dasyurids have a vascular retina. The arteries do not branch but form discrete capillary loops.



Immune System


Significant differences exist in the development of the immune systems of marsupials and eutherian mammals. No lymphoid tissue is present at birth, and the neonate is not immunocompetent. Most species reach immune system maturation at the time of first release from the maternal teat, approximately half way through pouch life. Passive transfer of maternal antibodies occurs throughout lactation, and antibodies are absorbed unchanged across the gut epithelium of the pouch young (PY). This passively acquired immunity is short lived, and most maternal antibody will be lost by about 4 weeks after separation from the mother, with the young only protected by an underdeveloped active immune system. Secretions from the pouch epithelium and macrophages found in marsupial milk may play roles in immunologic protection of the PY.52


In healthy macropod PY, the thymi are firm, bulging structures on the ventral side of the neck and may be visualized in unfurred or early furred PY. The thymi regress fully by sexual maturity.59 Superficial lymph nodes are not palpable in healthy macropods. The superficial inguinal, superficial axillary, rostral mandibular, mandibular, and facial lymph nodes are palpable in healthy koalas. Popliteal and subiliac lymph nodes are absent.25



Reproductive System


Marsupials have a diffuse, epitheliochorial choriovitelline placenta. Bandicoots have a diffuse placenta, with both choriovitelline and chorioallantoic contributions.66 Female reproductive anatomy is similar in all marsupials. Each of the paired lateral uteri opens into a vaginal cul-de-sac through its own cervix. The paired lateral vaginae both open separately into the urogenital sinus at the level of the urethral opening and are separated along their length by a soft tissue median septum (Figure 33-1). During parturition, the fetus tunnels through this septal tissue to form a median vagina. In most marsupials, the median vagina closes rapidly after passage of the fetus and then re-forms with each subsequent parturition. In most macropods, opossums, and the honey possum the median vagina becomes epithelialized after the first parturition and remains patent as a permanent median vagina.66



The anatomy of the male reproductive tract is similar in all marsupials. The scrotum is prominent, pendulous, pedunculated (other than wombats), and pre-penile. A strong cremaster muscle retracts the scrotal contents tightly against the body. Seminal vesicles and ampullae are lacking. Accessory sex glands consist of an often large disseminate prostate and one or more pairs of bulbourethral glands. In some species such as bandicoots, the prostate is easily palpated in the abdomen of breeding males.


The Macropodidae are the only marsupials to produce semen, which coagulates to form a seminal plug in the female’s urogenital sinus and vaginae after ejaculation14 and may be seen protruding from the female’s common vestibule.



Urinary System


The urinary system is similar in all marsupials. Unique to marsupials is the path of the ureters from the kidney to the bladder. The ureters pass between the median and lateral vaginae on each side. This anatomy has consequences for surgical procedures of the female reproductive tract. In macropods, the koala, and the wombats, the bladder is intrapelvic when not distended.


The urethra of male macropods has paired valvelike cusps approximately 2 to 3 centimeters (cm) proximal to the external orifice. Each cusp is approximately 5 mm long, with its free margin directed toward the external urethral orifice. A similar but larger pair of cusps lies immediately distal to the urinary bladder sphincter. These cusps may make urethral catheterization difficult. In koalas, two regions of the male urethra may potentially impede catheterization. The first is a narrowing of the lumen and some mucosal irregularity in the vicinity of the openings of the bulbourethral glands. The second is the prostatic sinus, a groove on either side of the urethral crest just distal to the neck of the bladder.



Metabolism and Thermoregulation


Brown adipose tissue, which is used by eutherians to generate heat, has not been found in marsupials.22 Some marsupials will enter one of two types of torpor. Shallow daily torpor in which the body temperature drops to 11° C to 28° C and lasts 2 to 20 hours occurs in opossums, dasyurids, small possums, and possibly in the numbat and marsupial moles. Deep, prolonged torpor (hibernation), in which body temperature drops to 1° C to 6° C and lasts 1 to 3 weeks occurs in pygmy possums (Burramyidae), the feathertail glider (Acrobates pygmaeus), and the Monito del Monte.21


Marsupials cannot thermoregulate until about half way through pouch life. Marsupial metabolism is lower than that of eutherians, with macropods at 25% and the koala and hairy-nosed wombats (Lasiorhinus spp.) very low at 44%. Basal metabolic rates are highest in the small insectivorous dasyurids (similar to eutherians), whereas rates for other dasyurids are less than half those in eutherian carnivores of similar size.30 All wombats, in particular the hairy-nosed species, have extremely low requirements of energy, protein, and water. Plasma concentrations of thyroid hormones in wombats are the lowest recorded for any mammal.4 Koalas and hairy-nosed wombats rarely drink fluids.


Thermoregulation is by evaporative mechanisms (panting, sweating, and licking). A unique feature of kangaroos is that sweating stops as soon as exercise stops, even if body temperature is still elevated and the animal is still panting rapidly.14,67 A method of evaporative heat loss by spreading saliva on the forearms is common in macropods that have undergone a period of exertion or anxiety. Panting is the major means of evaporative cooling in the koala. Wombats are more tolerant of cold than heat and cannot sweat, using postural thermoregulation or salivating on their forelegs and chest to aid cooling. Dasyurids do not sweat and cope with excessive heat by licking and panting to increase evaporative cooling.



Miscellaneous


Macropods have hearts one-third larger than those of comparably sized eutherian mammals and may move more air through their lungs with each breath.14 Hand-reared, adult macropods that have a nervous temperament may display a wide-eyed expression and trembling of the head, neck, and upper body when approached. This is termed tintibulation and is an apparent expression of anxiety or excitement. In the koala, the linea alba is broad and almost translucent, and no curtainlike omentum exists. Even in healthy, well-nourished captive koalas, fat depots are meager in comparison with those in most eutherian mammals.



Special Housing Requirements


Housing requirements for marsupials are diverse.32,70 Housing for hospitalization of ill or injured marsupials is described in Box 33-1.



Box 33-1


Housing Requirements for Hospitalization of Sick or Injured Marsupials

































































































Macropods68
Enclosure Simple, solid-walled (no objects protruding from the walls) standard hospital cages to stalls for larger species
Substrate Rubber matting, wood shavings, straw
Furniture Rock wallabies and tree-kangaroos should be provided with structures they may sit on top of or climb
Shelter Structures in which the animal may seek refuge, branches with leaves placed upside down in corners
Other Consideration should be given to the use of long-acting neuroleptic drugs
Koalas8
Enclosure Large enclosures allowing climbing both vertically and horizontally
Intensive care (IC) patients: standard hospital cages
Substrate IC patients: thick, soft padding covered with towel or blanket
Plastic floor matting allows urine to drain away
Furniture At least two resting forks, on the same or separate poles with a horizontal pole connecting the two
Rough-barked poles are easier to climb
A gently-inclined pole from the ground to a raised fork may enable a weaker koala to reach an elevated position
If very weak or unable to climb, a stable fork or other structure for support at ground level will be required
Other Drinking water should be made available in a stable shallow bowl on the floor
Wombats11
Enclosure Robust and escape-proof
A solid walled den or stall, avoid mesh or chain-link fences, standard hospital cages for IC and juveniles
Substrate Soil, sand, straw, leaf litter, wood mulch
If hospitalized for short periods do not need opportunity to dig and should be discouraged for debilitated or ill wombats as they may expend a large amount of energy
Shelter Burrow substitute to provide shelter and privacy: sturdy wooden box, large diameter concrete pipe, large hollow log
Other Common wombats <25° C, hairy-nosed wombats <30° C, supplemental heat for debilitated animals
Dasyurids28 and Opossums35
Enclosure 10 millimeters (mm) solid wood, glass fronted for small species, standard hospital cages for large species, sturdier accommodation with solid walls for quolls and Tasmanian devils
Substrate News, shredded or pelleted paper
Furniture Climbing structures for arboreal species, pool for water opossums
Shelter Wooden or cardboard nest boxes filled with shredded paper or wood shavings
Elevated for arboreal species
Other Supplemental heat may be required
For opossums 10–30° C (22° C most appropriate), humidity >58%
Possums and Gliders33
Enclosure Standard hospital cages covered with cloth or towel
Substrate Paper
Furniture Branches with leaves for cover and climbing
Shelter Elevated wooden nest box relevant to the size of the animal
Other Food and water bowls on the floor or elevated
Bandicoots and Bilbies41
Enclosure Standard hospital cages covered with cloth or towel
Walls should be solid or wire vertical bars, rather than mesh, to prevent nail damage
Substrate Nonabrasive (epoxy flooring, paper, clean towels)
Shelter Wooden or cardboard nest box relevant to the size of the animal
Other Can be kept in such enclosures for lengthy periods while under treatment, avoid frequent handling


Feeding


Compared with eutherians, most marsupials have a lower basal metabolic rate and therefore lower maintenance requirements for energy, protein, water and other nutrients. Requirements may generally be met with lower food intake and often fairly poor-quality, high-fiber diets. In captivity, marsupials are often fed in excess and fed concentrated diets of low fiber content, which results in obesity and dental and gastrointestinal (GI) disease.29 Energy intake should be monitored and controlled and activity encouraged through behavioral enrichment. Wild and captive diets have been described.2,4,17,32,70,71 Hospital and convalescent diets for marsupials are described in Box 33-2.



Box 33-2


Hospital and Convalescent Diets for Marsupials70



Macropods


Offer normal diet


Inappetent animals may be stimulated to eat with fresh grasses, browse, good-quality hay


Offer finely chopped, grated, or cooked food for animals with dental disease or extractions


Intensive care (IC) patients: offer or hand feed specialized herbivore intensive care supplements



Koalas


Encourage sick koalas to eat leaves


Offer fresh, high-quality leaves of various stages of growth and a variety of species, including known preferred species (sick koalas may change their leaf species preference)


Most do not hand feed and will not generally eat individual leaves removed from branches


May take leaves from small branchlets if not distracted by human presence


Supplementary feeding: low-lactose, high-energy milk powders mixed to a paste with water ± blended leaves



Wombats


Better able to tolerate extended periods of inappetence or anorexia because of low metabolic requirements


Offer a higher-energy diet, with greater quantities of foods such as sweet potato, sweet corn, carrot, apple, and higher-protein herbivore pellets


Grate items to tempt reluctant feeders


Tube feed (under general anesthesia) or “assist-feed” with a syringe, energy-rich mixes or specialized herbivore IC supplements for IC patients. Diazepam (0.1 milligram per kilogram [mg/kg], subcutaneously [SC], daily, 30 minutes before offering food) ± vitamin B complex (1 milliliter per kilogram [mL/kg], SC, once daily [SID], for 3 days) may stimulate appetite



Dasyurids, Bandicoots, Bilbies, Opossums, Possums, and Gliders


Add to standard diet: favorite food items, live insects, cat or dog food, cooked chicken, other meats, semi-solid or liquid convalescent carnivore diets (can be tube fed to IC patients) for carnivores or omnivores; and nectar mixes for possums and gliders


It is recommended that diets of small macropods be supplemented with vitamin E. Some small macropod species are prone to developing a syndrome of weakness and wasting of the hindlimbs, ultimately progressing to paralysis and death from myopathy. The development of this syndrome is not related to diet alone. Stress caused by overcrowding may increase vitamin E requirement.30



Hand Rearing


Successful hand rearing of marsupial PY requires a detailed understanding of neonatal development and physiology, the unique pouch environment, maternal care, passive immunity, development of the immune system, and milk composition.43 The major challenges in hand rearing marsupials are concerned with simulating the functions of the pouch, which provides a stable thermal environment until the PY becomes endothermic, and providing an appropriate milk substitute that may meet the changing needs of the developing PY until weaning and minimize exposure to pathogens.9


The milk of marsupials must support the PY from its embryonic state at birth until independence. The composition, therefore, changes profoundly during the course of lactation. The net effect of these changes is a gradual increase in energy content throughout lactation, meeting the increasing energetic demands of the growing PY as it becomes more active and develops endothermy. Calcium, phosphorus, sodium, and potassium concentrations also change during lactation.32,43,67


Marsupial milk has very low levels of lactose, oligosaccharides being the predominant carbohydrates for most of lactation. The transport of sugars into the intestinal mucosal cells is a relatively slow process. Mother-reared PY drink small volumes frequently. Hand-reared PY are fed larger volumes less frequently. When hand-reared PY are fed milk containing lactose, the capacity of the mechanism for transporting sugars into the cells is exceeded; hence unabsorbed lactose accumulates within the intestinal lumen, increasing the osmolality of the gut contents, resulting in watery diarrhea, dehydration, malabsorption of other nutrients, malnutrition, and retarded growth. Oligosaccharides are significantly larger than lactose and thus exert a lower osmotic effect.43,49


Numerous milk formulas have been used. Critical factors in the choice of a formula are low lactose content, and the formula should mirror the changing composition of natural milk from early to late lactation. A number of formulae that satisfy these requirements are available.43 Nevertheless, hand-reared PY of a wide range of species have thrived on a wide range of formulae, and the formula chosen is not the only key to success. Hygiene, husbandry, stress management, consistency, carer experience, and a maternalistic, nurturing instinct are equally as important.


The weaning process needs to be carefully managed for many species. Herbivorous species require inoculation of the gut with appropriate bacteria at this time. Hand-reared koalas that have not consumed pap must be fed natural pap or a substitute. Macropod and wombat young should be given access to fresh feces from healthy adults or mixed with water or formula and fed as a slurry.



Restraint and Handling


Capture and Physical Restraint


The principles of capture and physical restraint of marsupials is not different from those of other taxa, and appropriate methods have been described.27,32,70 The unique factor in marsupials is that females may eject the PY during pursuit and restraint. Excessive fear, exertion, or both may result in capture myopathy in macropods (see Box 33-9). Smaller species may spin violently when held by the tail, which results in fractures or dislocations.


Macropods may be caught in large, wide-mouthed hoop nets or by hand by grasping the base of the tail. Koalas may be encouraged to back into a bag. Docile koalas may be picked up from behind, by grasping around the wrists; alternatively, first the wrists and then the ankles may be grasped so that the koala is restrained in a sitting position, facing away from the handler. Wombats may be approached from behind and quickly grasped just behind the front legs with both arms. Small marsupials may be caught in a nest box or small enclosure by hand (protected by small towel or cloth bag) or small net. Larger dasyurids and opossums may be caught in a net or by grasping the tail between midway and the base.


Once captured, the animal should be physically restrained for only minor and quick procedures or anesthetic induction. All but the most tractable animals should be transferred into a bag for examination, drug administration, or transport. The head should remain covered at all times. Macropods held for longer periods should be suspended in bags off the ground. The animals should be kept cool.



Chemical Restraint27,70


Injectable chemical restraint agents may be administered by hand, intravenously (IV) or intramuscularly (IM), or remotely by using darts in larger species. In wombats, the sacral plate over the rump makes it impossible to give injections or dart in this area. Inhalational agents may be administered via a face mask or induction chamber (small species) or via an endotracheal tube after induction. Intubation of macropods, koalas, and wombats may be difficult. They have a narrow gape and dental arcade, and the distance from the oral opening to the larynx is substantial. Koalas have a long soft palate. In macropods and wombats, lateral recumbency, with the head extended, is preferable, whereas in koalas, intubation is possible in lateral, sternal, or dorsal recumbency. A long, narrow-bladed laryngoscope, a small rigid endoscope, or a long, curved transilluminator may be used to visualize the glottis. Long endotracheal tubes are required. A guide stylet may be inserted into the trachea and the endotracheal tube passed over it. Blind intubation may also be achieved by grasping the larynx between the thumb and forefinger of one hand and passing the endotracheal tube over the tongue with the other until the tube touches the glottis. As the animal takes a breath and air is heard rushing through the tube, the tube is inserted into the trachea. Larger dasyurids, possums, gliders, bandicoots, bilbies, and opossums are easily intubated with the aid of a small, narrow-bladed laryngoscope. A stylet may be required. For some possums and gliders, ventral recumbency, with the neck extended and head held vertically (similar to intubating a rabbit), may be used.


Preanesthetic fasting is not generally necessary for macropods, koalas, wombats, bandicoots, and bilbies; however, regurgitation may occasionally occur (particularly in macropods), and intubation is recommended for longer procedures. Preanesthetic fasting for 6 to 8 hours is recommended for dasyurids and 1 to 2 hours for larger possums, gliders, and opossums. In koalas, periods of apnea and, in unintubated animals, respiratory stridor caused by the long soft palate is relatively common. Profound and prolonged tranquillization has been seen in wombats with the use of long-acting neuroleptic agents. Ptyalism, poor relaxation, constant limb and jaw movements, and prolonged recoveries may be seen with tiletamine/ zolazepam in some species. In addition tachycardia, respiratory depression, apnea, muscle rigidity and deaths have been seen in possums and gliders.


Box 33-3 provides a list of chemical restraint agents, regimens, and doses used in marsupials.



Box 33-3


Chemical Restraint Agents, Regimens, and Doses Used in Marsupials.27,70



























Macropods


Koalas Wombats


Sedation or Tranquillization


Diazepam 0.5–1 mg/kg, IM; 0.5 mg/kg, IV




Dasyurids Bandicoots and Bilbies


Sedation or Tranquillization


Diazepam 1–2 mg/kg, IM




Possums and Gliders Opossums




Sedation Tranquillization


Diazepam 0.5–2 mg/kg, IM, orally (PO), IVd




image



a Joe Smith, personal communication.



b Simone Vitali, personal communication.




d Doses for Virginia opossum.35



Surgery4


Common indications for surgery are repair of traumatic injuries (soft tissue and bone), repair of tissues damaged by infectious processes, tumor excision, GI accidents, exploratory laparotomy, and reproductive procedures. Most of the procedures below are described for macropods but are equally applicable to other marsupial species.



Laparotomy


Consideration must be given to the voluminous GI tract in some species, the presence of a pouch (with or without PY) in females, and the epipubic bones. With the animal in dorsal recumbency, a ventral midline approach is used. If access to the caudal abdomen is required, tilt the body head down to about 30 degrees. In both sexes, when access to the cranial abdomen is required, the approach is straight forward. In females with a pouch, the approach will depend on the size of the pouch and the presence of PY. If the pouch is empty or the PY may be temporarily removed, a midline incision may be made inside the pouch, midway between the teats and the cranial border of the pouch. A useful technique is to use stay sutures to hold the pouch open. If a PY is present and cannot be removed, an incision may be made lateral to the pouch opening at the cranial end of the epipubic bone. The skin is then reflected toward the midline to expose the linea alba.


In the koala, extreme care is required when opening the abdominal cavity through a ventral midline incision. Subcutaneous fat is absent; the linea alba is thin; the abdominal muscles are 2 to 3 mm thick over the ventrolateral abdominal wall; and the cecum and proximal colon lie immediately below the incision site.8



Surgical Sterilization


Ovariectomy and Ovariohysterectomy


The animal is prepared as for laparotomy, and the head is tilted down to 30 degrees. An incision is made midway between the tip of the epipubic bones and the pubis. The reproductive tract is visualized, and one side exteriorized with the use of a spay hook. For ovariectomy, one uterus is located, and the corresponding ovary is exteriorized. The fimbria and ampulla of the oviduct are teased off the ovary to enable clear visualization of the ovarian vessels. The vessels are clamped and ligated, and the ovary is removed. Complications such as pyometra have not been reported.


Ovariohysterectomy is technically more difficult and risky because of limited access and the unique anatomy of the reproductive tract. The only indication for the surgery may be therapeutic reasons. The approach is as for ovariectomy. A hole is made in the broad ligament just lateral but close to the ovaries to avoid catching the ureters (which should be visualized). The ovaries are exteriorized with gentle traction on the suspensory ligament. The vessels are clamped and ligated. Once both ovaries are ligated and detached, the broad ligament is torn off, staying as close to the lateral margins of the blood vessels as possible to avoid damaging the ureters. The uteri are ligated at the immediate proximal end of the cervices (see Figure 33-1). They are first ligated separately, and then a single ligature may be placed around both uteri. Transfixation ligatures may be required. Once the uteri are removed, a continuous suture to close the stump may be necessary.


Sterilization of koalas and macropods may also be performed via laparoscopic tubal ligation or ovariectomy. The animal is positioned as above. Following routine surgical preparation, the abdomen is insufflated with carbon dioxide (CO2). Three small incisions are made to allow insertion of the grasping forceps, laparoscope, and cautery scissors into the caudal abdomen. For tubal ligation, each oviduct is visualized and manipulated with the forceps so that transection and cautery may be achieved. For ovariectomy, the ovary is manipulated and elevated with the grasping forceps and removed from the ovarian bursa. Electrocautery (with or without endoclips for large animals) is used to ligate the ovarian vessels. Laparoscopic long-blade scissors are then used to free the ovary from its abdominal attachments. Once free, the cannula is retracted through the skin incision to allow direct removal of the ovary from the abdominal cavity through the incision.



Orchiectomy and Scrotal Ablation


The animal is placed in dorsal recumbency. The scrotal septum is prominent, and the testicles are removed through separate incisions in the scrotum on each side at the most ventral point. A standard open castration technique is used. The incisions are left open. For scrotal ablation, castration is performed, as described above; however, the spermatic cords are severed at as high a point as possible. The scrotal pedicle is cut flush with the abdominal wall. The ligated spermatic cords are pushed through the incision toward the inguinal canal. The wound is closed. Orchiectomy and scrotal ablation in sugar gliders with the use of a CO2 laser to sever the scrotal stalk has been described.50



Vasectomy


With the animal in dorsal recumbency, an incision is made, midway between the testicle and the abdominal wall, in the skin and tunica vaginalis over each spermatic cord on the cranial side of the scrotal pedicle. A small portion of the spermatic cord is exteriorized and the vas deferens identified, bluntly dissected out, and exposed. A segment is removed after ligating proximally and distally to the piece being removed. Vas deferens clips may be used. The wounds are sutured.



Orthopedics


All standard orthopedic principles and techniques may be readily applied to fracture repair in marsupials. In macropods, the unique anatomy of the hindlimbs and the massive mechanical stresses that are placed on the bones of the hindlimbs and pelvic girdle during locomotion make adequate stabilization of fractures of these bones difficult. The prognosis for successful repair in adult macropods is generally poor. Hand-reared PY that may be confined to a pouch during convalescence are better candidates for fracture repair. External fixateurs have been used with success to repair fractured tibias in older hand-reared macropods. In small species and perhaps the tamest of larger species, fractures of the metatarsi may be repairable with either internal or external fixation.



Miscellaneous Procedures


Tail amputation has successfully been performed in macropods, with the animals adapting well to the loss of the tail, despite the obvious reliance on the tail for a pentapedal gait.65,68 Standing up from lateral recumbency may occasionally be a problem. A standard technique for tail amputation is used.


Cataract surgery in macropods is technically easy; however, many cases develop postoperative glaucoma, probably secondary to chronic uveitis. The prognosis even with treatment is poor, and many cases require globe evisceration or enucleation or euthanasia. In PY with galactose-induced cataracts, surgical removal of the lens often reveals extensive opacification of the vitreous, making the prognosis for return to normal vision poor. Because of these complications it is difficult to justify cataract surgery in macropods.62


Conjunctival ablation in koalas may be indicated (as an adjunct to topical treatment, systemic treatment, or both) in chronic cases of chlamydial disease, where proliferative conjunctivae obscure vision.8



Therapeutics


Few pharmacokinetic studies have been conducted in marsupials, and drug doses are usually extrapolated from those for domestic animals. As a general rule, drugs seem to be well tolerated and appear to contribute to improvement in clinical condition. It has been proposed that the lower metabolic rate of marsupials should be accounted for by reducing dose and frequency of administration when extrapolating data from eutherian mammals. Recent studies indicate that this is not valid, and some evidence suggests that hindgut-fermenting marsupials may have specific mechanisms for dealing with plant toxins and xenobiotics.18,44,64


Several pharmacokinetic and efficacy studies on marsupials have been published.7,15,16,23,24,37,38,46,48 The koala studies are consistent with what is known about their efficient metabolic pathways and also suggest barriers to oral and subcutaneous absorption.


Very few reports of precautions and adverse drug reactions in marsupials are available. Subadult common ringtail possums (Pseudocheirus peregrinus) appear to be particularly sensitive to antibiotics. A dysbiotic syndrome leading to wasting and death (similar to that seen in other hindgut fermenters) has been reported. In macropods there have been anecdotal reports of dysbiosis in macropods, particularly after oral administration of antibiotics (particularly penicillins). Hand-reared PY are prone to developing candidiasis when on antibiotics (see Box 33-6). Mebendazole toxicity has been described in macropods.58 Wasting and death within 2 to 6 weeks of administration of parenteral oxytetracycline and oral erythromycin has been reported in koalas.8 Nystatin may induce diarrhea when used at higher doses.

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Aug 27, 2016 | Posted by in EXOTIC, WILD, ZOO | Comments Off on Marsupialia (Marsupials)
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