There are 28 species of Australian possums and gliders in six Families. The smallest have an adult body size of less than 10 g while the largest may weigh up to around 4.5 kg (Smith & Winter 1984). All gliders and nearly all possums are arboreal and live in forest or heathland, but some are semi-terrestrial including the mountain pygmy possum (Burramys parvus), rock-haunting ringtail (Petropseudes dahli) and scaly-tailed possum (Wyulda squamicaudata) (Strahan 1995). Due to this habitat requirement, most species are found along the coast and associated ranges. Only a small number of species are found in Tasmania. Many species have a restricted range but some, such as the common brushtail (Trichosurus vulpecula), common ringtail (Pseudocheirus peregrinus) and sugar glider (Petaurus breviceps) have extensive ranges (Smith & Winter 1984). In addition, common brushtails and common ringtails often live in urban areas (How & Kerle 1995; McKay & Ong 1995). These two species are the most common seen in veterinary practice in Australia. Sugar gliders are commonly kept as pets in other countries and the common brushtail was introduced to New Zealand in 1858; it is now a major agricultural and ecological pest there (Tyndale-Biscoe 2005a).
Possums and gliders are nocturnal although some, such as the common spotted cuscus (Spilocuscus maculatus), the feather-tailed glider (Acrobates pygmaeus), the honey possum (Tarsipes rostratus) and the eastern pygmy possum (Cercatetus nanus), may sometimes be active in daylight hours (Renfree 1995; Turner & Ward 1995; Winter & Leung 1995; Woodside 1995). During the day they shelter in constructed nests or pre-existing structures such as tree hollows or rocky outcrops (Menkhorst 1984). Common ringtail and feather-tailed glider nests are known as dreys. These are spherical bark or leaf nests made in tree hollows or suspended in undergrowth (McKay & Ong 1995; Woodside 1995). The basic social unit of possums and gliders may consist of an individual or stable, often family-based group depending on species (Russell et al. 1989). All possums and gliders have cutaneous scent glands and para-cloacal glands that are important for communication. Saliva, urine and faeces are also used for scent marking (Biggins 1984; Dawson et al. 1989; McKay 1989). Some species, such as the yellow-bellied glider (P. australis), common brushtail and sugar glider are very vocal (Biggins 1984; Suckling 1995).
Mountain pygmy possum
Eastern pygmy possum
Herbert River ringtail possum
Source: Menkhorst (2001).
2 ANATOMY AND PHYSIOLOGY
The limbs and tails of possums and gliders reflect their generally arboreal niche (McKay 1989; McKay & Winter 1989; Russell & Renfree 1989; Turner & McKay 1989). The pads of the digits and feet are often granulated or corrugated, which enhances friction. The fore feet are variably arranged between species. Some species such as ringtail possums have a grasping hand with the first two digits opposable to the remaining three (McKay 1989). The striped possum (Dactylopsila trivirgata) uses an elongated fourth fore limb digit and long tongue to extract ants and termites (Smith 1982). Digit one of the hind foot is laterally directed, clawless and opposes the remaining digits. Digits two and three of the hind foot are reduced in size and united by skin (syndactyly) (Smith & Winter 1984). The tails of possums and gliders are long, at least moderately prehensile and often have a hairless friction pad on the underside. Gliders use the tail as a rudder. The tail of the feather-tailed glider has distinctive lateral fringes of long stiff hairs, giving it a feathery appearance, and pygmy possums can store fat in their tail base (McKay 1989; McKay & Winter 1989; Russell & Renfree 1989; Turner & McKay 1989).
Gliders are distinguished from possums by the presence of a gliding membrane (patagium) extending from the hind limb to the fore limb. The gliding membrane consists of a fold of skin, connective tissue and muscle. In Petaurus spp. it extends from the fifth digit of the fore foot to the distal metatarsus or first digit of the hind limb. In the greater glider (Petauroides volans) and feather-tailed glider it extends from the elbow to the distal tibia and stifle respectively. There is elongation of the long bones of the larger gliders (McKay 1989; Suckling 1995; Woodside 1995).
Gliding is a more efficient form of movement than running, climbing or jumping. It enables animals to move quickly from tree to tree, facilitating efficient foraging. Gliding also reduces the need to come to the ground, ensuring that animals remain clean and dry. Scent trails are broken by gliding, which reduces the risk of predation. The gliding membrane provides warmth when wrapped around the body (Lindenmayer 2002).
The pouch opens cranially, has 2–6 teats and may have an incomplete median septum in Petaurus spp. and Leadbeater’s possum (Gymnobelideus leadbeateri) (McKay 1989; McKay & Winter 1989; Russell & Renfree 1989; Turner & McKay 1989). Eccrine sweat glands are restricted in distribution to hairless areas. Cutaneous scent glands are found in all animals and include sternal, frontal, lip and tail glands. Para-cloacal glands also appear to be present in all species (Biggins 1984; Dawson et al. 1989; McKay 1989). The sternal gland in brushtail possums (Trichosurus spp.) is an obvious brown patch which is best developed in males and appears most prominent during the breeding season (McKay & Winter 1989).
The pollen and nectar feeding pygmy possums and the honey possum have a long brush-like tongue with long fine filiform lingual papillae. These probably increase the uptake of nectar. Pollen is mainly collected on the fur and ingested during grooming. In the honey possum, nectar and pollen are removed from the tongue with a series of transverse ridges on the hard palate, some of which have spines (Richardson et al. 1986).
Possums and gliders have diprotodont dentition (Smith & Winter 1984). They have lower incisors reduced to a single functional pair of large procumbent (reclining) teeth, three pairs of upper incisors, variably present canines, one or two pairs of upper and lower premolars and four upper and lower molars. The premolars and molars are well-developed with cusped grinding surfaces. In contrast, the honey possum has flew teeth which, with the exception of the lower incisors, are reduced to peg-like structures (Richardson et al. 1986; Russell & Renfree 1989; Turner & McKay 1989).
Most possums and gliders digest plant material by microbial fermentation in the caecum and colon and have a simple stomach. An expanded caecum is the main site for fermentation in most species. The intestines of the striped possum and honey possum, however, are simple due to the lack of plant material in their diet. The stomach of the honey possum has a large diverticulum, which may have a role in nectar storage (Hume 1982; Smith 1982; Richardson et al. 1986). Coprophagy of caecal contents occurs in at least the common and green ringtails (Pseudochirops archeri) (Strahan 1995; Winter & Goudberg 1995).
Pygmy and honey possums and the feather-tailed, sugar and yellow-bellied gliders enter torpor in response to cold or decreased nutrient intake. They also huddle to conserve energy (Fleming 1980; Russell & Renfree 1989; Turner & McKay 1989; Lindenmayer 2002). Torpor usually last for less than a day. During winter the mountain pygmy possum is able to undergo extended periods resembling true hibernation, with intermittent short periods of normal body temperature and activity (Broome 1995; Geiser & Broome 1993; Geiser 1993). The feather-tailed glider can hibernate for up to 5 d during which its body temperature may decrease by up to 2°C (Fleming 1985; Lindenmayer 2002).
3.1 Reproductive anatomy
The anatomy of the female reproductive tract is typical of most marsupials. There are two lateral vaginae and a median vagina with a temporary central canal through which the young is born. The morphology of the reproductive tract changes with the stage of the breeding cycle. For example, in female sugar gliders the ovaries, lateral vaginae and uteri increase in size during oestrus and early pregnancy. Sugar gliders have elongated lateral vaginae compared with other species of possums and gliders (McKay 1989).
The anatomy of the male reproductive tract of possums and gliders is similar to that of most marsupials. Testes are located in a pre-penile scrotum. Accessory sex glands consist of only a prostate and one or more pairs of bulbourethral (Cowper’s) glands (Temple-Smith 1984). The glans penis is commonly bifid for a short distance terminally, e.g. in ringtail possums and pygmy possums, or may be tapered with (e.g. common brushtail) or without (e.g. honey possum) a urethral process and may have short backward projecting spines (Russell & Renfree 1989; Turner & McKay 1989). When not erect the penis forms an S-shaped curve and is withdrawn into the common vestibule. Sperm production and testes size vary seasonally in the greater glider and the common ringtail (Temple-Smith 1984). The prostate gland and bulbourethral glands of the male sugar glider increase in size during the breeding season, as does the prostate gland but not the testes of the common brushtail (Temple-Smith 1984; Lindenmayer 2002). In some species such as the common brushtail, males may be fertile all year and sperm production and testes size do not vary (McKay 1989). In brushtails a post-copulatory plug that forms from prostatic fluid after mating may prevent subsequent insemination by other males (Kerle 2001).
3.2 Reproductive physiology
Most possums are polyoestrus and polyovular, except for some of the larger species which may be monovular (Kerle 2001). Ovulation occurs on the first 1–2 d of the oestrous cycle. Ovulation is usually suppressed by lactation but females will return to oestrus 8–9 d after losing a PY. Length of gestation is usually less than 60% of the length of the oestrous cycle. However, in mountain pygmy possums, pygmy possums and the honey possum, gestation is longer (Table 12.2).
All gliders are polyoestrus, except for the greater glider which is monoestrus. It also has a short breeding season (March–June). It normally produces one young per year, but will give birth to a second young if the first is lost early in the breeding season. Males produce sperm from March to May, after which the testes reduce in size (Kerle 2001).
Embryonic diapause has traditionally been recognised as a characteristic of macropods. However, diapause has also been described in the honey possum (Oates et al. 2007), the feather-tailed glider and the eastern pygmy possum (Renfree 1981).
Monogamy is reasonably common in most of the larger species of possums and gliders. The smaller species that live in colonies, such as the honey possum, feather-tailed glider, eastern pygmy possum and mountain pygmy possum, are usually polygamous.
Body size is closely related to reproductive parameters such as age at weaning, litter size and growth rate. Larger species produce fewer eggs, have smaller litters and longer lactation periods and their young have lower growth rates. Twinning is common in sugar gliders and common ringtails and occurs occasionally in common brushtails (Hughes & Hall 1984).
Diet, particularly protein content, influences litter size and growth rates of possums and gliders (Lindenmayer 2002). Low protein in the diet of the greater glider may contribute to the production of only one offspring annually, a long lactation period and slow growth rate. The short breeding season of the greater glider corresponds with a short period during which protein levels in eucalypt leaves increase. In comparison, the yellow-bellied glider has a more varied diet and a much longer breeding period of up to 9 mo (Table 12.2). The Herbert River ringtail (Pseudocheirus herbertensis) has a bi-modal breeding season. A major breeding season occurs in early winter and a second shorter period in summer. Leadbeater’s possums may give birth in any season, with peaks in autumn and spring (McKay 1989). These two species are indigenous to more tropical regions of Australia; the more tropical species tend to breed year round. In the sugar glider, spring breeding coincides with increased availability of protein-rich insect prey.
3.3 Emergence from the pouch
Postnatal growth has been described in the sugar glider, squirrel glider (Petaurus norfolcensis), common ringtail and Herbert River ringtail (McKay1989). The general pattern of development is similar to that of other marsupials. After leaving the pouch, the offspring of Pseudocheirus spp. may remain with their mother, clinging to her fur as a back young. In the Herbert River ringtail and Petaurus spp. they may be left in the nest. The age at dispersal varies with species (Table 12.2).
The principles of exhibit design and husbandry for possums and gliders have been reviewed (Jackson 2003). Due to their nocturnal habits the use of reverse day/night cycles is common in the display of most species. Adequate space and height for climbing, exploring and escape from conspecifics is required due to the increased chance of intraspecific aggression in some species in captivity. Common brushtails, common ringtails, eastern pygmy possums, sugar gliders, squirrel gliders and feather-tailed gliders are the most commonly kept exhibit animals. Yellow-bellied gliders and Leadbeater’s possums are kept to a lesser extent in zoological collections in Australia. Sugar gliders are popular pets in North America and the United Kingdom. They are social animals and need to be housed in groups. A typical captive colony comprises one dominant male, two subordinate males and four females. Young should be removed at or soon after weaning to avoid being killed. Adult animals should be checked daily for evidence of fight wounds (Booth 2000). If sugar gliders are kept as pets at least two animals are required (entire males housed together will fight). Unfortunately, in many cases they are kept in isolation as a single pet and frequently develop behavioural problems such as stereotypies. Feather-tailed gliders live in large colonies.
4.1 Hospital and rehabilitation housing
Housing requirements vary according to species, age and sex. If indoor hospitalisation is required, conventional dog or cat cages can be used as long as a nest box and other cover such as leaves are provided and the wire fronts of the cages are covered in mesh fine enough to prevent escape. Animals should always be housed in a quiet environment physically separated from dogs and cats. Animals undergoing rehabilitation can be kept outdoors in secure aviaries in more temperate climates. More solitary species such as common brushtails should be housed singly. More social species such as sugar gliders and common ringtails can be successfully group-housed outdoors in wire mesh pens with dirt, grassed or concrete floors. They should be placed in groups of two or three before being moved into outdoor aviaries. Pens should be well-constructed and vermin- and bird-proof. Outdoor pens should include adequate shelter from extremes of temperature, wind and rain (ANZCCART 2006). Sufficient numbers of nests or nest boxes should be supplied to provide a safe retreat should animals be threatened by each other. Two hanging wire baskets tied together and lined with coconut husk fibre, fine twigs, leaves or other plant material create a comfortable nesting drey for common ringtails (Fig. 12.1). Branches for climbing should also be provided. Gliders should have adequate space for gliding.
4.2 Individual marking and identification techniques
Identification techniques vary for different species, ranging from eartags and ear notching to implanting of passive integrated transponders (microchips). The use of microchips for the identification of individual animals is the most common and practical method. Implants are inserted SC between the scapulae. In smaller species this is best performed with the animal under anaesthesia. The needle hole should be closed using tissue glue to prevent the microchip falling out soon after implanting. Ear notching has been used in feather-tailed gliders and small species such as pygmy possums. Metal eartags are also commonly used.
Nest boxes removed from an enclosure with the animal secured within it can be used for transport. The nest box should be placed in a cat carry cage or pet pack for added security. Most species are readily transported in cloth bags (calico or hessian) which are then placed in a secure and well-ventilated container for transport over longer distances. For transport over long distances animals may be placed in secure wooden boxes with adequate nesting material (e.g. shredded paper) for comfort and cushioning during the journey. Gentle encouragement from one container or enclosure to another is preferable to direct handling.
Possums and gliders may be herbivorous, insectivorous, folivorous, nectivorous or omnivorous. Foods include leaves, fruit, flowers, seeds, sap, gum, insect exudates, insects and occasionally meat (brushtail possums, common spotted cuscus). Some species are specialist feeders and rely entirely on honey and pollen (honey possum), ants (striped possum) or leaves (greater glider) (Smith 1982; Russell et al. 1989; Russell & Renfree 1989).
Common brushtails are cosmopolitan in their dietary habits and eat native foliage, fruits and flowers, some animal protein and insects. They have adapted well to urbanisation and scavenge food scraps and eat exotic flowers and fruits.
Common ringtails eat a wide variety of native flora including the leaves of eucalypts and melaleucas. Although primarily folivorous they also eat native fruits and flowers, especially grevilleas and wattle. They also eat introduced plants such as roses and cultivated fruits. Common ringtails are coprophagic. They produce two types of faeces. Caecotrophs (large soft moist faecal pellets originating from the caecum) are produced during daylight hours when the possum is less active and are eaten immediately. Coprophagy ensures more efficient absorption of nutrients. Harder faecal pellets are passed during the more active nocturnal period and are not usually eaten.
Gliders tend to be more selective. Sugar and squirrel gliders are sap eaters but also eat seeds, including wattle and casuarina, nectar, pollen and insects. They particularly favour psyllids and lerps (or scale insects) and the waxy sweat scale-like covering they produce. They do not eat leaves, flowers or buds. Feather-tailed gliders feed on nectar, pollen, sap, small insects, lerps and flowers. The yellow-bellied glider, the largest of the Petaurus genus, eats the sap from a large variety of eucalypts. Like other members of the genus they also eat insects and nectar. Greater gliders are almost exclusively folivorous, preferring the leaves of a wide range of eucalypts. They also eat the fruit of turpentine (Syncarpia spp.) trees.
Captive animals or those undergoing rehabilitation should be offered a diet as close as possible to that of free-ranging animals. Specific diets for captive possums and gliders have been reviewed in the literature (Jackson 2003; Booth 1994). Suggested daily diets for captive common brushtails are based on a mixture of fruit and vegetables, for captive ringtail possums a mixture of fruit, vegetables, leaves and flowers and for captive sugar gliders fruit and invertebrates such as moths or crickets. This basic diet should be supplemented less frequently with other dietary components (Table 12.3).
The intake of the captive diet can be assessed by monitoring weight, skin and body condition and faecal consistency. Obesity is common in captive possums and gliders due to a plentiful food supply and reduced exercise (Booth 2000). For example, captive sugar gliders are often fed an excess of fat and simple sugars. Mealworms are high in fat and should be avoided or fed only in low quantities. Moths, beetles and crickets provide behavioural enrichment. The inclusion of pine nuts, casuarina seeds and acacia seeds in the diet contributes to good dental health.
Flowers (at least 2×)
Leaves (at least 2×)
Sunflower seeds (2×)
Sunflower seeds (2×)
Soaked dry puppy food (2×)
Dry dog food (3×)
Boiled egg (2×)
Sunflower seeds (2×)
Boiled egg (2×)
Mineralised salt lick (ad lib)
Egg yolk (2×)
Possum nectar mix (1 ×)
Leaves and flowers (3×)
Mineralised salt lick (ad lib)
Possum nectar mix (1 ×)
Possum nectar mix (3X)
Leadbeater mix (1X)
200 g baby rice cereal (e.g. Farex®)1
21 g high-protein baby cereal1
1 tspn glucose powder
1 hard-boiled egg white
1 tspn nutritional supplement powder (e.g. Sustagen®)2
150 mL honey (preferably Eucalypt based)
4 drops infant multivitamin drops (e.g. Pentavite®)3
1 level measure Sustagen®2
Combine the above ingredients and make into a slurry
Blend the above ingredients and add water to make a total volume of 750 mL
Store refrigerated for up to several days
Sources: Booth (1994); M Lynch (pers. comm.).
Manufacturers: 1 Heinz Watties. 2 Mead Johnson Nutritionals. 3 Roche.
Disease syndromes related to poor or inadequate nutrition are common in pet sugar gliders. Owners commonly offer a wide choice of foods, which may lead to nutritional imbalances. Animals tend to select soft sweet fruits which tend to be low in calcium and high in simple sugars. Feeding fruit and a high-sugar diet to folivores such as the common ringtail can lead to bloating with gas or fluid. This condition is frequently irreversible and may be fatal.
6.1 Capture and physical restraint
Capture of free-ranging possums and gliders can be difficult; various techniques have been tried (Goldingay & Kavanagh 1991; Harris & Goldingay 2005; Wayne et al. 2005). Common brushtails are readily trapped in cage traps (Fig. 12.2).
Restraint techniques vary according to species, size and the degree of injury or pain suffered. Pillowslips, small linen bags or sacks for larger species are useful for restraint and transport. Nest boxes or logs with removable lids are useful as the animals are frequently in the box or log and can be readily transferred from box to bag. Most species can be readily picked up, with a towel or cloth bag to cover the hands. Even the larger gliders can be handled this way. Gloves should not be used except perhaps with brushtails. Possums can be held by the tail, but they may turn around and bite. Brushtails and common ringtails can be grasped with one hand on the tail base or rump and the other around the neck and shoulders. This technique should only be used by experienced operators in brushtails as there is a risk of being bitten and of compromising the animal’s breathing (Jackson 2003; Booth 1994) (Fig. 12.3). It is relatively straightforward in ringtails. Physical restraint can be used for minor procedures such as brief examination, medicating or handling prior to induction of anaesthesia. If in a bag, injections can be given through the cloth. Anaesthetic masks may be held over the muzzle of the animal while it is restrained in a bag or nest box. Cat squeeze cages may be used to restrain more fractious animals such as common brushtails for injection. Hollow logs or plastic plumbing pipe can also serve as restraint devices allowing access to the rear of the animal. Captive possums and gliders can become very tame, particularly if handled regularly.
6.2 Chemical restraint
Sedation may be useful prior to inhalation anaesthesia or for minor procedures and transport. Diazepam (0.5–1 mg/kg IM) or butorphanol tartrate (0.4–1 mg/kg SC or IM) have been used (A Olsson & J Roffey pers. comm.).
Pre-anaesthetic fasting for 1–2 hr prior to anaesthesia is adequate as regurgitation under anaesthesia is uncommon in possums and gliders. Pre-anaesthetic handling should be minimised in order to decrease common complications of anaesthesia, such as breath-holding and apnoea. It can be difficult to assess the anaesthetic risk of a patient prior to induction; body mass and demeanour may aid in assessing risk. Approximate body weights of selected possums and gliders are presented in Table 12.1.
Inhalation anaesthesia using isoflurane in oxygen delivered via a face mask and Ayre’s T-piece provides rapid induction in most cases and is the method of choice for induction and maintenance of anaesthesia (Vogelnest 1999; Holz 2002; Booth 2003). Induction with 4–5% isoflurane and oxygen flow rate of at least 1 L/min (200 mL/kg body weight) reducing to 2% isoflurane for maintenance is recommended. In smaller species such as the feather-tailed glider and the eastern pygmy possum an induction chamber may be used with a mask used for maintenance. However, most clinicians prefer masking as animals may become distressed in induction chambers (A Olsson pers. comm.).
Maintenance is usually via mask, however, larger species are easily intubated with the aid of a narrow-bladed laryngoscope. In some cases a stylet may be required. Intubation of sugar gliders has been described using a 1 mm endotracheal tube with stylet and a narrow-bladed laryngoscope (Booth 2000). Small-diameter tubes should be removed at regular intervals during the procedure to check for patency due to the risk of blockage with mucus.
Injectable anaesthetic agents are rarely required but may be useful if inhalation anaesthesia is not available, in field situations or with animals that are difficult to restrain. Ketamine has been used on its own or in combination with other drugs. Duration of anaesthesia and recovery time appear to be dose-related and the swallowing reflex appears to be preserved. Used alone, doses of 10–30 mg/kg are recommended for restraint of common ringtail and brushtail possums depending upon the desired level of restraint (T Bellamy pers. comm.). Surgical anaesthesia was induced within 2 min and lasted about 19 min in common ringtails and cuscuses administered 9–17 mg/kg IM (Salas & Stephens 2004). No adverse effects were observed.
More commonly, ketamine is combined with xylazine or medetomidine, which provides smoother induction and recovery. Doses vary. In common brush-tails, ketamine (2–3 mg/kg IM) can be combined with xylazine (2–5 mg/kg IM) and antagonised with yohimbine (0.2 mg/kg IM). However, others have recommended much higher doses of ketamine (30 mg/kg IM) combined with xylazine (6 mg/kg) without apparent ill effects (Holz 2002; Holz 2003). Ketamine (1–3 mg/kg IM) and medetomidine (0.02–0.1 mg/kg IM) have also been used successfully (Vogelnest 1999). Restraint is antagonised with atipamezole (0.05–0.4 mg/kg IV).
Tiletamine/zolazepam is commonly used in larger species of both captive and free-ranging possums (4–10 mg/kg IM). Induction is usually rapid and smooth with good muscle relaxation. Reported adverse effects include tachycardia, ptyalism, respiratory depression, apnoea and muscle rigidity (Vogelnest 1999; Holz 2002; Viggers & Lindenmayer 1995). Three deaths have been reported in squirrel gliders (Holz 1992). Recovery can be prolonged. It is dose-related and recovering animals must be monitored closely to ensure patency of the airway. One report suggested that the dose required (up to 20 mg/kg) for restraint and anaesthesia of possums is higher than that for other species (Booth 1988; Viggers & Lindenmayer 1995). This is not the author’s experience and lower doses are usually adequate. An advantage of using tiletamine/zolazepam is the low volume required and the rapid induction. Tiletamine/zolazepam can be combined with an a2-agonist such as medetomidine to provide smoother induction and recovery. Tiletamine/zolazepam does not have a specific antagonist but when combined with medetomidine the medetomidine can be reversed with atipamezole at 5 times the medetomidine dose (0.05–0.4 mg/kg IV or IM). Recovery is rapid (Vogelnest 1999).
Alfaxalone (5–8 mg/kg IM) has been used effectively to anaesthetise common brushtails (R Johnson pers. obs.; S Gelis pers. comm.). Using 5 mg/kg IV provides rapid short-acting anaesthesia in common brush-tails and common ringtails, which is useful for brief and relatively non-invasive procedures or for surgical induction. Induction is smooth and recovery rapid and uneventful. Tiletamine/zolazepam (1–3 mg/kg IV) or propofol IV (6 mg/kg) have also been used (Vogelnest 1999).
6.2.3 Local anaesthesia
Bupivacaine 0.5% administered directly onto traumatic or surgical wounds while under general anaesthesia complements other analgesic medications and allows lower levels of chemical restraint. This technique is useful when debriding fight wounds, burns and other skin lesions.
7 CLINICAL PATHOLOGY
7.1 Haematology and biochemistry
7.1.1 Sample collection
Possums and gliders can be physically or chemically restrained for venipuncture. Chemical restraint is preferred as it has the advantages of providing immobility and reducing the effects of excitement on some haematological parameters (Jain 1993). Common sites for blood collection are the jugular vein (under general anaesthesia), lateral saphenous vein, caudal tibial artery and lateral caudal (tail) vein. Brushtail possums, ringtail possums and larger gliders can be bled from the jugular or lateral saphenous vein using a 22 or 23 G needle; for smaller gliders and possums a 25 G or 27 G needle should be used. A scalp vein or butterfly catheters may facilitate collection in smaller species. The caudal tibial artery, located superficially on the medial aspect of the stifle, has been used in species sugar glider size or smaller as an alternative to the lateral saphenous vein (Booth 1999; Clark et al. 2004). The lateral caudal vein is superficially located and suitable for blood collection even in small species.
Other sites for vascular access include the cephalic, femoral, ventral caudal and ear veins, the heart and the periorbital sinus (Presidente & Correa 1981; Hemsley 1992; Viggers & Lindenmayer 1996, 2001; Wells et al. 2000; Clark et al. 2004). The ventral caudal vein is located in the ventral midline of the tail and is found by inserting the needle perpendicular to the skin surface close to the tail base until bone is encountered. The needle is then withdrawn slowly while gentle negative pressure is applied, until blood enters the syringe and a blood sample can be withdrawn (Clark et al. 2004). This site may be useful in smaller species. In sugar gliders, venipuncture can be attempted blindly between the thoracic inlet and the angle of the mandible (Booth 2000). While these sites can be used in most species, more superficially located vessels, which can be visualised, are preferred. Very small volumes of blood can be collected into capillary tubes from incised or pricked superficial veins such as an ear vein or lateral caudal vein or the heel. Cardiac puncture allows collection of relatively large volumes of blood from any species but risks of pericardial haemorrhage, pulmonary laceration and haemorrhage or damage to the heart indicate that it should be used only in anaesthetised animals just prior to euthanasia (Clark et al. 2004; Hemsley 1992). Orbital sinus bleeding using a pipette or capillary tube might be considered in very small species such as the honey possum but it is an invasive procedure which can result in significant ocular damage (Nagy et al. 1995; Van Herck et al. 1998). Both cardiac puncture and orbital sinus bleeding should be avoided in favour of less invasive techniques.
7.1.2 Reference ranges and interpretation
Haematology and biochemistry values for possums and gliders are limited (Tables 12.4 and 12.5). Common brushtails have been the most extensively investigated. In this species age, sex and reproductive status all influence values. Haemoglobin concentration, haematocrit, erythrocyte counts and serum total protein concentrations are lower in immature animals and haemoglobin concentration, haematocrit and erythrocyte counts in adult males are higher than females (Barnett et al. 1979; Presidente & Correa 1981; Viggers & Lindenmayer 1996). Mothers with large young have lower haematocrit and haemoglobin and serum total protein concentrations than non-lactating females or those with small young (Presidente & Correa 1981). Seasonal effects have been reported in short-eared possums (T. caninus), with higher levels of urea and serum protein in spring and summer respectively, possibly due to variation in dietary protein intake (Barnett et al. 1979; Viggers & Lindenmayer 1996). Occasional circulating nucleated erythrocytes have been reported in apparently normal common brushtails, sugar gliders, striped possums and yellow-bellied gliders (ISIS 2002; ISIS in-house, Taronga Zoo 2005). There is little published information on the haematological and biochemical responses of possums and gliders to physiological and pathological processes. Until this becomes available, clinical judgment based on responses as seen in eutherian mammals may be appropriate.
Urine can be collected by cystocentesis from anaesthetised animals or by opportunistic collection of voided samples. There are no published reference ranges for normal possum and glider urine. Samples from three common brushtails and two common ringtails without evidence of urinary dysfunction were light to moderately yellow. It was clear to slightly turbid in the common brushtails and moderately turbid in the common ringtails, possibly due to amorphous sulphate and sometimes urates, which have been reported as making the urine of the latter species turbid (Cunningham 1994; Hemsley 1992). Urine specific gravity was 1.011–1.030 in the brushtails and 1.034–1.040 in the ringtails and pH was 6.0–6.5. Trace protein and glucose levels, indicated by commercial dipstick tests, were most likely spurious results. It should be noted that normal common brushtail urine is sometimes red, presumably due to the presence of pigments.
8.1 Reasons for orphaning
Orphaning of free-ranging possums and gliders is commonly a result of the mother being preyed on by dogs and cats or suffering motor vehicle trauma. In captivity, mothers have been known to abandon PY due to a range of stressors.
Low-lactose formulas available for possums and gliders in Australia include Di-Vetelact (Sharpe Laboratories), Wombaroo (Wombaroo Food Products) and Biolac (Biolac Milk Products). Biolac offers several formulas within the one brand, increasing the total solids (fat and protein) content as dietary requirements change from the furless or just furred PY to those emerging from the pouch. Two stages of Wombaroo possum milk are available, <0.8 and >0.8, the latter with a higher fat and lower protein content than the former. The formula required depends on the PY’s stage of development. According to the manufacturer, the possum milk replacers are suitable for all species of possums and gliders.
8.3 Prognosis for different age classes
Generally, furless PY are much more difficult to rear than furred ones and even in the hands of experienced carers hand-rearing can be difficult. Factors to consider before commencing the task of hand-rearing a furless PY include the increased chance of problems arising later in the hand-rearing process (failure to thrive, diarrhoea) and the time, expertise and expense involved, which may be used more productively in caring for animals with a better prognosis. More importantly, undue distress to the PY and emotional attachment may be avoided if the decision not to rear is made sooner rather than later. Furless PY should be checked for palatal and lip injuries as they are often pulled off the teat, causing trauma to the oral cavity. PY should be carefully examined for the presence of any cat bite wounds.
Experienced carers recommend that common brushtails under 70 g body weight should not be hand-reared (Bishop 2005; Smith 1995). The survival rate of furless common ringtails is poor (Stanvic 1992). Possums considered for hand-rearing should, at the very least, have a fine velvety covering of hair. Common ringtail PY as small as 30 g have been raised successfully (Bishop 2005), but the survival rate improves rapidly once they reach the 60–80 g weight range (Smith 1995). Sugar gliders less than 10 g cannot be reared successfully but PY are relatively easy to rear once furred (Stanvic 1992).
8.4 Rearing techniques
Due to the high incidence of multiple births and their social habits, common ringtails and sugar gliders are best raised in groups. Substitute pouches for hand-rearing can be made from a variety of materials including calico or wool with a woven cotton liner. Hairless possums can be wrapped in a cotton handkerchief then the end of a stocking. Pouch young are unable to thermoregulate adequately and require supplementary heating at earlier stages of rearing. Furless PY should be kept at 34–3 6°C gradually reducing to 30°C as fur develops. After emerging the PY can be moved to a more natural environment, with the pouch suspended over a heating pad. As the animal matures the heating pad can be removed during the day and later at night as well (Tables 12.6–12.8). Heaters should be thermostatically controlled to avoid both hyperthermia and hypothermia. The pouch is a high-humidity environment and furless PY are subject to drying of the skin. Moisturisers such as lanolin should be applied frequently. Temperature and humidity should be regulated, e.g. with a humidicrib, but an alternative is commercially available bird hotboxes with a thermostatically controlled heating source and humidity provided via an open container of water in the box (Stanvic 1992; Bellamy 1994).
Formula should always be fed at a comfortable temperature (36°C) (Bellamy 1994). Guidelines for volumes required at different growth stages are mentioned below, but manufacturers’ recommendations for use should be referred to. Syringes or eyedroppers with attached custom-made teats (longer than dog and cat teats) are used. For very small animals bicycle tyre valve rubber, a plastic IV catheter, infant gastric feeding tube or trimmed infusion set tubing may be used instead of a teat to achieve small and uniform droplet flow (Bellamy 1994; Smith 1995). During the feeding process it may be easier to keep the PY within the pouch, limiting movement. Older furred young can be encouraged to lap from a spoon or dish (Fig. 12.5). After each feed the perineal area should be gently wiped with a warm moistened tissue to stimulate defecation and urination. Overzealous wiping will cause inflammation and dermatitis and, occasionally, prolapse of the cloaca. This process should be continued until at least the 80 g stage in common ringtails and 300 g in common brushtails (Smith 1995). Furred PY should be brushed with a soft brush (Stanvic 1992). If reared in isolation from adults, inoculation of the gut with micro-organisms is recommended as digestion relies on hindgut fermentation. This is most easily accomplished by allowing access to faeces of adult conspecifics (Finnie 1976), but donor faeces should first be smear tested to ensure that yeasts are not present.
Frequency of feeding depends upon the PY’s stage of growth (Tables 12.6–12.8). Furless PY should be fed every 2–3 hr, which reduces gradually to around 5 times per day when fur is developing and to 2–3 times per day at full emergence from the pouch. It is important to keep good records and measure and weigh the PY at least 3 times per week.
The total amount of formula fed daily depends on the composition of the formula, but should generally be 10–20% of body weight per day except in very small PY when up to 50% of body weight may be needed (Bellamy 1994). The volume of milk to be fed varies according to manufacturer recommendations.
The following suggested volumes are based on Wombaroo® product information (E Arthur pers. comm.).
Common ringtails should be drinking 2–3 mL/day at 6 g body weight, increasing to 4 mL at 10 g and 11 mL at 50 g. At this stage milk should be offered in a bowl to encourage lapping. When ringtails start to emerge from the pouch, at approximately 75 g, they should be drinking 15 mL daily. This volume should not be increased, to encourage feeding on solids. Full emergence occurs at 120 g body weight.
Common brushtails should be drinking up to 6 mL/day at 20 g body weight, increasing to 11 mL at 50 g. At 80 g body weight the PY should be offered milk in a bowl to encourage lapping. At this stage they should be consuming 18 mL daily. Once they reach 120 g the volume increases to 20 mL. Pouch emergence begins at 130 g, the PY being fully emerged at 400 g when it should be consuming about 46 mL daily.
At 6 g body weight sugar gliders should be drinking 3 mL/day, increasing to 4 mL daily at 10 g. At this stage native browse should also be offered. PY heavier than 12 g usually lap from a shallow spoon. At the start of pouch emergence (20 g) PY should be consuming 5 mL daily. At 50 g they take up to 9 mL daily, and are fully emerged from the nest. Sugar gliders are ready for release once they reach 80 g body weight, when they should be consuming up to 10 mL of formula daily.
8.4.3 Solid food
During the hand-rearing process a variety of solid food as similar as possible to the natural diet should be offered (Smith 1995). For common ringtails this includes the tips and flowers of eucalypts, tea trees (Leptospermum spp.), bottlebrush (Callistemon spp.) and paperbark (Melaleuca spp.) as well as grevillea and wattle flowers. Hand-reared common ringtail PY should not be offered fruit as the high sugar content can predispose to bloat (see 9.8.3). For common brushtails, bark, the tips and flowers of eucalyptus, grevillea, bottlebrush and wattle can be offered. They also occasionally eat insects, such as beetles or crickets. Some fruit and vegetables such as apples, carrots, pears, rockmelon, grapes and sweet potato can be offered. Sprinkling food with a commercially available high-protein baby food supplement is recommended. For sugar gliders, natural dietary constituents such as insects, pollen, nectar, lerps, thrips, borers and the sap of eucalypts and other native trees should be offered if possible. In addition, apple, rockmelon, grapes, grevillea, banksia and wattle flowers can be offered. A high-protein supplement is recommended.
A common concern is apparent constipation in common ringtails a few weeks after weaning commences. The possum appears healthy and has a good appetite but no longer defecates on stimulation and faeces are no longer found in the artificial pouch. The animals are always normal on examination. It is thought that this must be the stage when they commence caecotrophy during the day; carers fail to find the small hard pellets passed during nocturnal foraging. After becoming aware of this situation carers generally look for and find these pellets (McCracken 2001).
8.4.4 Transition to release
At approximately 100–200 g body weight hand-reared common ringtails should be transferred to a large bird cage (approximately 900 × 900 × 900 mm). There should be a nest box hanging inside the cage and the wire mesh should be no larger than 19 × 19 mm. Multiple cages can be placed side by side to encourage socialisation. At 300–450 g body weight they should be moved to a release aviary. A suitable release weight for common ringtails is 700–800 g. Common brushtails can be moved to an aviary at 700–800 g body weight. It is important to reduce contact with the animal at this stage in order to facilitate release, which occurs at around 1400 g body weight in common brushtails. Sugar gliders need to be transferred to an aviary at 60–70 g to encourage jumping and gliding to build muscle mass and fitness. They are ready to release at 80–90 g.
9.1 Dermatological diseases
A variety of skin conditions have been diagnosed in possums and gliders. Alopecia occurs frequently in most species and may be discrete patches, diffuse and extensive and symmetrical or asymmetrical. Causes include epilation after an attack by a predator, stress, nutrition, hormones, PY being maintained at too high a temperature or infectious causes (see 9.9.3). Investigation to rule out infectious causes should occur in all cases, but in many cases no specific aetiology is determined. Despite this, identification and correction of potential underlying causes frequently results in resolution.
Bacterial and fungal skin disease is common. Mycotic dermatopathy involving yeasts (Candida spp.) and mixed bacterial infections, often including Pseudomonas aeruginosa, has been seen in feather-tailed gliders (ARWH 2007 case numbers 1468/1, 1468/3, 1468/5, 2192/1, 3650/1, 4674/1). Animals affected ranged from juveniles to adults of both sexes. Accompanying disease conditions included pneumonia, pleuritis and sinusitis. Dermatitis, epidermitis, cellulitis, pyoderma, panniculitis and severe ulceration of the skin have been recorded in common ringtails, sometimes in association with fungal infection (ARWH 2007 case numbers 730/1, 2110/1, 2221/1, 2537/3, 2793/1, 4094/1, 4133/1, 4470/1).
Ectoparasites, viruses and systemic diseases have also been associated with skin problems. A case of exudative dermatitis in a common ringtail was associated with a heavy infestation of the mite Trichosurolaelaps striatus (ARWH 2007 case number 730/1). Poxvirus was suspected as the cause of papillary dermatitis in a common ringtail (ARWH 2007 case number 4133/1). Thyroiditis was diagnosed at necropsy in two common ringtails with skin disease (ARWH 2007 73/1, 2793/1). One animal had bilaterally symmetrical alopecia (73/1), the other had marked ulcerative dermatitis (2793/1). No thyroid function tests were performed on these animals prior to death.
9.1.1 Exudative dermatitis in common brushtails
Exdative dermatitis, also known as lumbosacral dermatitis or rumpiness, is common in common brushtails (Reddacliff 1981; Hemsley 1992; Hemsley & Canfield 1993b; Hemsley 1994). There is chronic ulcerative or proliferative dermatitis and a neutrophilic leukocytosis (Hemsley 1994). Lesions typically include alopecia, exudation, crusting and in severe cases ulceration in the lumbosacral or tail base region; they can also occur on the face, trunk or limbs (Fig. 12.6). An offensive odour is often present and the fur is matted and easily depilated. The aetiology of the condition is unclear but is likely to be multifactorial and may involve hypersensitivity, a variety of ectoparasitic, bacterial and fungal agents, trauma and stress (Finnie 1978; Reddacliff 1981; Munday; 1988; Hemsley 1994). Mixed bacteria such as Staphylococci, Streptococci and Corynebacteria are commonly present (Reddacliff 1981; Hemsley 1994) but are likely to represent secondary infection. Trichosurolaelaps crassipes mites are the common ectoparasite associated with lesions. However, a recent study monitoring a wild population of mountain brushtails (T. cunninghami) indicated that there is no obvious correlation between pelage condition of the rump, ectoparasite loads, general health parameters or inflammation of the skin. Damage to the pelage of the rump in that population of mountain brushtails seemed to be influenced by season, gender and habitat. Trichosurolaelaps dixoa, Atellana papilio and Haemolaelaps penelope were the most commonly collected mites. Ticks identified included Ixodes tasmani, I. trichosuri and I. cornuatus and one Acanthopsylla spp. was found (Hufschmid 2005). The rat mange mite, Notoedres muris, has been recorded as the cause of crusty lesions affecting the ears, tail, snout and eyelids of brushtail possums in Victoria (Booth 1994). The species of possum was not mentioned.
Figure 12.6 Exudative dermatitis (a) on the legs of a common brushtail and (b) on the face of a common brushtail. Note the large numbers of stick-fast fleas, Echidnophagia myrmecobii, at the base of the ear. Photos: a) Robert Johnson and b) Larry Vogelnest.
Possible predisposing factors may include prolonged periods of rain, high humidity and overcrowding (Reddacliff 1981). The condition is most common in subadult and adult males and where population density is high, possibly indicating an association with territorial disputes and social stress (Munday 1988). It is frequently seen in dispersing subadult males. Some cases have been associated with underlying disease processes such as anaemia, encephalitis, hepatitis, lymphadenopathy and pneumonia (Hemsley 1994). Many animals that present with exudative dermatitis are also victims of trauma such as dog attack, possibly being more susceptible because of debilitation.
When deciding if cases of exudative dermatitis should be treated consideration must be given to the animal’s fate once it has recovered. Releasing the animal into an area where it will be re-exposed to the environmental and social stressors that led to its condition may not be in its best interests. Euthanasia should be considered in severe cases, particularly young males (L Vogelnest pers. comm.). Treatment may be successful when there are no significant confounding factors present. A systemic acaracide such as ivermectin 200 μg/kg SC or a topical preparation such as selamectin (6 mg/kg topically once a month) should be used when mites are present (J Roffey pers. comm.). Topical antibacterial treatment of skin lesions is frequently required in addition to parenteral therapy although mild lesions may heal after a single injection of long-acting penicillin (Reddacliff & Spielman 1990). More severe cases may require a longer course of oral or parenteral antibiotics such as amoxycillin or amoxycillin/clavulanic acid (20 mg/kg sid SC or IM or bid PO for up to 4 wk) (L Vogelnest pers. comm.). Possums frequently resent applications of medications, especially on raw or ulcerated lesions. Spray preparations of chlorhexidine 0.05% can be used, or compliant animals may be placed in a pillowslip and gently lowered into a shallow bath of chlorhexidine 0.05% for 1–2 min, ensuring that the head is above water at all times. In severe cases, anaesthetised animals may need to be clipped and bathed using antiseptic shampoo. Ointments containing silver sulphadiazine and chlorhexidine digluconate (Silvazine®, Smith & Nephew) or other commonly available topical antibiotic, antifungal and corticosteroid preparations may be applied.