Wombats are diprotodont marsupials in the Family Vombatidae, and are most closely related to the koala. They occur only on mainland and off-shore islands of Australia, including Tasmania. There are three species in two Genera. The common wombat (Vombatus ursinus) lives in temperate forests and forest edges of south-eastern Australia, where habitat is suitable for burrowing. Its density is limited by food availability. There are three subspecies, which are found on the mainland, Flinders Island and Tasmania (Strahan 1995). The southern hairy-nosed wombat (Lasiorhinus latifrons) inhabits semi-arid grasslands and is limited to areas of South Australia, western Victoria and far eastern Western Australia. When habitat and climate are suitable, it can be found in significant numbers. The northern hairy-nosed wombat (Lasiorhinus krefftii) also lives in semi-arid grasslands and is now restricted to Epping Forest National Park in central Queensland. It is critically endangered with only about 100 animals remaining (IUCN Species Survival Commission 2001). The range of all three species has decreased significantly since European settlement (Strahan 1995).
Common wombats and southern hairy-nosed wombats are often kept in zoos and wildlife parks. Wild and orphaned wombats of these two species are often presented for veterinary care. No northern hairy-nosed wombats are kept in captivity (Horsup 1998).
The three wombat species are broadly similar in appearance. The common wombat has bare skin on the nose and a coarse short coat. The ears are small and rounded. In contrast, hairy-nosed wombats have longer silky fur, soft furred muzzles and longer pointier ears. Northern hairy-nosed wombats are similar in appearance to the southern species, with a larger square muzzle (Strahan 1995). Adult wombats of all three species weigh about 20–35 kg. Males are larger than females except in the northern hairy-nosed species where females are larger in every dimension except neck girth (Johnson & Crossman 1991).
All three species of wombats were viewed as pests by European settlers and have been subject to persecution by land owners. Perceived problems include degradation of the environment through burrowing, damage to fencing and grazing competition with stock. In more recent times, burrows of southern hairy-nosed wombats have interfered with underground telecommunications cables.
Until the mid 20th century, common wombats were declared vermin with a bounty on their heads and in some cases there were attempts to eradicate populations. In most areas, wombats are now protected but land holders may obtain permits to cull if they are causing damage (Triggs 1996).
Other threats to wombats include land clearing, introduced and endemic diseases, motor vehicle trauma, inadvertent poisoning and predation by dogs and foxes. Changing pasture composition (from native perennial to annual and exotic plants) as a result of domestic stock or rabbit grazing may have a significant negative effect on wombat populations (Strahan 1995).
Wombats, in particular the hairy-nosed species, have a great ability to survive in a harsh drought-susceptible environment due to their energetically frugal lifestyle (Evans et al. 2003). They are dependent on their burrows and spend most of their time underground, emerging in darkness to graze. Burrows provide protection against predators, bushfire and, most importantly, extremes of temperature and humidity (Tyndale-Biscoe 2005). Common wombats build fairly simple burrows, whereas hairy-nosed wombats create extensive multi-entrance warren systems which may be occupied by several animals at the same time. All wombats are expert burrowers, using their fore limbs for digging and their incisors for cutting and removing obstacles. The hind limbs move soil away from the excavation site (Wells 1989).
Wombats occupy relatively small home ranges (up to 25 ha). Common wombats are solitary and defend their individual territories during contact with other wombats in areas where population densities are high. Hairy-nosed wombats may form loose social communities, sharing warren systems. Wombat territories may overlap extensively. Individuals stake their territories by scent-marking with dung and urine, scratching in dirt wallows and rubbing pheromones on posts, tree trunks and similar landmarks (Johnson 1998; Strahan 1995). Olfaction is the primary communication method; they also communicate through a variety of vocalisations including growls, grunts, huffs and squeals.
2 ANATOMY AND PHYSIOLOGY
Wombats are large, herbivorous, mainly nocturnal burrowing marsupials. They have stocky powerful bodies with short muscular limbs, well-suited for digging. They have a number of anatomic and physiological specialisations which allow them to thrive in their environmental niche.
2.1 Musculoskeletal system
Wombats have large flattened heads, thick skulls, solid jaws and a short neck. Both pectoral and pelvic girdles are strong. The short muscular legs and strong clawed feet are ideally suited for burrowing. There are five digits on both front and hind feet. The first digit of the hind foot is reduced to a small nub and the second and third toes are syndactylus. Wombats walk on the soles of their feet with a characteristic rolling gait. They walk, trot or bound and are capable of moving at high speed (40 km/hr) for short distances when necessary (Wells 1989). Wombats have a very short vestigial tail.
The skin of wombats is considerably thicker than that of other marsupials and quite inelastic. Wombats of all three species have a characteristic sacral plate on the rump which is almost as rigid as bone. The plate is used to help compact burrow walls and may also provide protection against predators.
2.3 Digestive system
Wombat dentition is specially adapted to cope with grazing high-fibre high-silica grasses. All teeth are rootless and continue to grow throughout life. Wombats have one pair of incisors, one pair of premolars and four pairs of molars in both upper and lower jaws. Wombats are diprotodont (one pair of lower incisors) but are unique in that they are the only diprotodont marsupial with one pair of upper incisors. The cheek teeth are hypsodont and the incisors have enamel over the labial surface only. The differential wear between the harder anterior enamelled surface and the softer dentine covering the posterior surface of the incisors results in the maintenance of a chisel-like biting edge (Murray 1998). All species of wombats have a split upper lip. This allows the wombat’s incisor teeth to delicately pick individual blades of grass close to the ground. They use their molars and specialised jaw musculature to grind food to an extremely fine particle size, much finer than any other grazing marsupial (Tyndale-Biscoe 2005).
Wombats are hindgut fermenters with a simple gastrointestinal system, a simple stomach (with a cardiogastric gland), a relatively short small intestine, a very large sacculated colon and a very small caecum. Proteins and soluble carbohydrates are digested in the stomach and absorbed in the small intestine. The majority of energy is derived from bacterial fermentation in the colon. Wombats have a slow gut passage time (averaging 3 d but up to 8 d). This, along with the fine particulate size of ingesta, enables them to extract maximum energy and moisture from their generally poor-quality natural diet. Wombat faeces are among the driest of any animal (Hume 1999).
2.4 Reproductive system
Female reproductive anatomy is similar to that of other marsupials. The ovaries occupy an ovarian bursa. There are paired lateral uteri each of which 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. During parturition the foetus tunnels through this septal tissue to form a median vagina. The urogenital sinus enters the common vestibule or cloaca at the level of the termination of the rectum (Tyndale-Biscoe & Renfree 1987).
There are two mammary glands located over the caudal ventral abdominal wall of the pouch, although wombats only raise one PY at a time (Wells 1989). The wombat pouch is rear-opening with a well-developed sphincter muscle. Pouch condition varies with reproductive status. In the juvenile animal the two teats are small and inverted and the pouch is little more than a shallow pocket held closed by the strong sphincter. Teats become everted at sexual maturity, at 2+ yr of age. As the wombat grows the pouch deepens and is often observed to be soiled, containing an exuded dry brown scale, dust and other debris (Wells 1989).
The male has a pre-penile non pendulous scrotum, a relatively large carrot-shaped prostate and three pairs of bulbourethral glands. There are no seminal vesicles or ampullae (MacCallum 2004). The non-erect penis has a sigmoid flexure and occupies a preputial sac adjacent to the cloacal opening. The glans is bifurcate and, proximal to the bifurcation, there are a series of caudally directed spines arranged circumferentially around the penile shaft. The size of the testes, prostate and paired bulbourethral glands (located either side of the cloaca) increases in sexually mature males during the breeding season, most notably in the hairy-nosed wombats (Wells 1989).
2.5 Metabolism, water balance and ecological adaptations
All wombats, in particular the hairy-nosed species, have extremely low energy, protein and water requirements. They are able to maintain condition on a low-quality and often low-quantity herbivorous diet. Hairy-nosed wombats have a very low basal metabolic rate, only 64% of the average marsupial, or 44% of the average placental mammal. The metabolic rate of common wombats is close to that of the average marsupial (Hume 1999).
Hairy-nosed wombats receive sufficient moisture from their diet and do not need to drink. Wombats recycle urea, releasing it back into the hindgut where it aids bacterial proliferation. Because less urea is excreted in the urine, water turnover is further reduced (Tyndale-Biscoe 2005). The kidneys of the common wombat are proportionally much larger than those of the hairy-nosed wombat, however, the urine-concentrating ability of the hairy-nosed species appears to be far greater (McAllan et al. 1995). Under most conditions, wombats do not produce highly concentrated urine as they maintain water balance primarily through ecological adaptations and the ability to resorb moisture from the colon (Wells & Green 1998).
The low body temperature of wombats (34–35°C) also conserves energy and water. In the hairy-nosed wombat, body temperature falls below this level during burrow resting times (Strahan 1995). Plasma concentrations of thyroid hormones in wombats are the lowest recorded for any mammal (see Table 9.3) (Barboza et al. 1993).
All wombats are more tolerant of cold than heat. Wombats cannot sweat, but in warm environments they lie on their backs, shedding heat by exposing their thinly furred axillae and inguinal areas. Wombats may also salivate on their fore legs and chest to aid cooling (Wells 1989).
Wombats alter their behaviour patterns in response to environmental conditions. They spend much of their time resting or sleeping in their burrows, which maintain remarkably stable environmental conditions despite extreme fluctuations in temperature and humidity on the ground surface. The average daytime temperature in a southern hairy-nosed wombat burrow is 26°C in summer (compared to 38°C outside) and 14°C in winter (2°C outside). The thermoneutral range of the hairy-nosed species is 14–26°C (Tyndale-Biscoe 2005). High humidity in the burrow minimises water loss (Wells 1989).
On average wombats spend 2–6 hr a day grazing, but if conditions are unsuitable they may not emerge from the burrow at all (Tyndale-Biscoe 2005). In winter, they may emerge from burrows to graze in late afternoon, avoiding the falling temperatures of night. In hot months they graze closer to dawn, seeking the coolest temperatures and maximising moisture intake through dewfall. Throughout the day, wombats will move to different areas of the burrow to micromanage their ambient temperature and humidity (Tyndale-Biscoe 2005).
Wombats, like most burrowing mammals, are physiologically tolerant of low oxygen and high carbon dioxide levels (Tyndale-Biscoe 2005). Because burrowing requires large amounts of energy and time, newly independent young wombats occupy burrows already constructed and vacated by adults (Johnson 1998).
Olfaction and hearing are the best developed and most important senses in wombats. Vision is better developed and more important for wombats than traditionally assumed (Strahan 1995).
Study of reproductive behaviour and physiology in wild wombats has been hampered by the fact that they are nocturnal, fossorial and cryptic. Lack of breeding success in captive animals has limited the opportunity to study wombat reproduction in zoos.
Reproduction conforms to the marsupial pattern. There is a brief in utero phase, birth of altricial young and an extended and sophisticated lactational phase of which a significant proportion is spent in the pouch. Wombats have a relatively long intergenerational interval due to a long pouch life and period of association with the dam before independence. Under optimal conditions, female wombats raise only one offspring every 2 yr. In drought conditions, ovulation in the female southern hairy-nosed wombats and sperm production in the male may cease (Strahan 1995). Successful reproduction depends on good-quality forage near the burrow, to support both the lactating female and the weaned young (Tyndale-Biscoe 2005).
3.1 Reproductive physiology
Female wombats are monovular and polyoestrus. There are some notable differences in the reproductive strategy of common and hairy-nosed wombats. Southern hairy-nosed wombats have a defined breeding season with births occurring between November and January (Gaughwin & Wells 1978).
Free-ranging common wombats have seasonal peaks of breeding with variations, dependent on latitude and altitude, which coincide with optimum pasture availability (Strahan 1995). Births can occur at any time of year but are most frequent around spring (Moritz et al. 1998).
An early report based on urogenital cytology estimated oestrous cycle length in common wombats to average 33 d (Peters & Rose 1979). More recent studies have estimated the cycle to be significantly longer than this. One study based on behaviour and the measurement of plasma and faecal progestogens reported a mean oestrous cycle length of about 55±11 d (Paris et al. 2002a). Another study based on vaginal cytology and plasma progestogen analysis reported oestrous cycle length in the common wombat to range between 45 and 51 d (West et al. 2004). Ovulation is likely to be spontaneous in wombats.
There are no reliable estimates of the length of gestation in common wombats. Estimates of southern hairy-nosed wombat gestational length are based on observations of a mating and subsequent appearance of a newborn PY 20–22 d later in a single individual (Crowcroft & Sunderland 1997).
3.2 Breeding and life stages
One study reported that the female wombat pouch became dirty 10 d after oestrus and clean again 9–6 d prior to oestrus (Peters & Rose 1979). The periparturient pouch is also observed to be clean and moist (Triggs 1996).
Cyclic increases in activity, vocalisation and aggression have all been reported in female wombats thought to be in oestrus, as has swelling of the urogenital opening (Peters & Rose 1979). However, there have been no reports validating these indicators of oestrus by correlation with breeding behaviour, endocrine changes or visualisation of gonads. One study revealed that a male common wombat displayed increased flehmen behaviour in the period before the female’s luteal phase, as defined by measured elevations in female faecal pregnanes, suggesting this male behaviour may be useful as an indirect indicator of oestrus (Paris et al. 2002).
In southern hairy-nosed wombats there may be an increase in aggressive behaviours during the breeding season. Males in particular may show evidence of bites, usually to the ears, rump and flanks. Vocalisations increase, including a cough-like vocalisation from the female when in oestrus (Wells 1978).
Courtship behaviour and mating has been observed in free-ranging common wombats. A report described chasing of the female by the male in circles and a figure-eight pattern. The female periodically slowed and allowed the male to catch up, whereupon he delivered a powerful bite to her hindquarters. She stopped in response to this and allowed the male to roll her on her side and mount. During copulation, which lasted approximately 3.5 min, the female moved from lateral to sternal recumbency. After mating the female broke from coitus and initiated another chase sequence during which several unsuccessful attempts were made by the male to bite her before she slowed again and the copulation/chase sequence was repeated. This occurred seven times over a 25 min period (Marks 1998). A report describing courtship and mating in a captive pair of common wombats divided the process into five phases:
- attraction—during which the female followed the male, made nose-to-nose contact when they passed and frequently stopped in front of and perpendicular to him presenting her cloaca by extending her hind limbs (3–4 min);
- interim—during which the animals called and responded with a series of grunts (2–3 min);
- chasing—during which the male chased the female attempting to bite her from behind (30 min);
- copulation—during which the male grasped the female around the hips, rolled onto his side and mated her (approximately 30 min);
- post-copulatory—during which the animals separated and lay in lateral recumbency (several minutes) (Boer 1998).
Courtship and mating have not been observed in free-ranging southern hairy-nosed wombats although captive mating events have been observed. In these animals copulation occurred in lateral recumbency and was preceded by the female’s resistance to mating attempts and the male biting the female’s hindquarters.
The life stages of the wombat are similar for all three species (Table 9.1). Early pouch life, where the young is altricial and pouch-dependent, continues up to 6 mo of age. After this time the PY’s head begins to emerge occasionally from the pouch. At 7 mo the PY begins to exit the pouch, in the safety of the burrow. Around 9 mo the young emerges from the burrow to graze beside the mother. At this time, common wombat young may feed on a special soft faecal pellet produced by the dam. It is thought that this fulfils the same requirement as pap feeding in koalas, to inoculate the developing herbivorous intestine with the necessary bacterial flora (Tyndale-Biscoe 2005). Wombats are usually weaned at 12–15 mo and remain at foot until independence, around 18 mo (Tyndale-Biscoe 2005). Adult size is reached at 2–3 yr, depending on food availability and growth rates. Sexual maturity occurs at 2–4 yr of age, with males reaching maturity later than females (Wells 1989). The average life span of a wombat is 12–15 yr, although individuals have lived up to 23 yr in the wild and 30 yr in captivity (Jackson 2003).
4.1 Captive housing
Wombats are strong powerful diggers and can chew through most materials. They are adept at climbing over barriers, swimming through water moats and crossing electric fences. Housing for wombats needs to be robust and escape-proof.
A solid walled den or stable can be used as a temporary holding area for a wombat. Wombats may damage themselves on mesh or chainlink fences and tend to pace and fret when there are no visual barriers. Floors should be solid (e.g. concrete) or have mesh buried under soil to prevent escape. Alternatively, fencing can be buried into the ground to a depth of 1 m. Wombats digging on concrete floors can damage their feet. Soil, sand, straw, leaf litter and wood mulch can be used as substrate. Damp floors may lead to foot problems. Wombats held in captivity for short periods do not need to have the opportunity to dig. When debilitated wombats first enter captivity, it is often advisable to limit their opportunity to dig as they can expend a large amount of energy on this behaviour. All wombats need a burrow substitute to provide both security and protection against temperature extremes. Suitable items include a sturdy wooden box, large diameter concrete pipe or large secure hollow log. Straw can be used as bedding in the shelter area.
Wombats held in long-term captivity should be provided with as much space as possible and the opportunity to dig. A minimum area of 45 m2 has been recommended for two wombats, with an extra 9 m2 for each additional wombat if housed in groups. Ideally, enclosures should be much larger than this to reduce the likelihood of escape and stress behaviours (Jackson 2003). Care must be taken with the type of soil substrate provided and the use of heavy enclosure furnishings such as boulders and logs, as burrow collapse has resulted in the death of captive wombats. Enclosures are typically surrounded by solid smooth lined fencing (concrete, building blocks, glass panels or sheet metal) to a minimum height of 1.2 m (Jackson 2003). Water-filled moats and electric fences are not reliable barriers for wombats. Outdoor enclosures should be secure against predators, including cats, which may transmit toxoplasmosis (Booth 1999). Shade and shelter from rain and wind should be provided over part of the main enclosure. Wombats held long-term may be housed indoors; reversed daylight cycles may be used to allow visitors to observe the animals during their more active hours. Wombats are generally only active for a few hours each day and spend the remainder of the time frugally conserving energy. Behavioural enrichment for long-term captive wombats should include the provision of an adequate depth of soil for digging; browse, logs and branches (with bark attached) and native grasses (planted in enclosures or provided in clumps with roots and dirt attached) for animals to chew and dig up (Jackson 2003) along with a high point (such as a dirt mound or boulder) for surveying the territory and posts for scent-marking (Fig. 9.1).
Wombats are susceptible to heat stress and captive wombats need to be housed in an appropriate thermal environment. Common wombats may suffer heat stress at temperatures above 25°C whereas hairy-nosed wombats tolerate temperatures up to 30°C (Tyndale-Biscoe 2005). Air-conditioning, misting sprinklers and climate-conscious exhibit design, including a well-insulated burrow system and a well-ventilated outdoor area, can be used to maintain appropriate environmental temperatures. Debilitated animals may need supplemental heat in the form of a heat lamp. When ambient temperatures are cooler, wombats like to bask in the sunshine.
Wombats in temporary care should be housed individually. In long-term captivity, hairy-nosed wombats may be housed in compatible groups. Common wombats are often housed individually in captivity, although hand-reared animals are frequently paired up as juveniles (same or opposite sex pairs) and may remain compatible for life. More details on short-term and long-term housing of wombats including complex captive burrow systems can be found in Booth (1999) and Jackson (2003).
4.2 Care in captivity
Although they appear to be stoic and robust animals, wild wombats often adapt poorly to the captive environment. Human interference and other disturbances (loud noises, domestic animals) should be kept at a minimum.
Wombats may not show obvious signs of stress. Indicators include loud vocalisations (‘screams’); teeth gnashing; aggression (such as biting, scratching or charging without prior threat displays); pacing and escape behaviour. Escape attempts and pacing may not be readily observed and may only occur at night. Signs of pain in wombats include listlessness, teeth grinding and pawing at the abdomen. Chronic stress may manifest as bilateral alopecia or generalised immunosuppression with other disease processes developing (Spielman 1994).
Sick wombats should be disturbed as little as possible. Fresh food and water should be provided daily (although wombats are seldom seen to drink) and enclosure hygiene must be well-maintained. Health observations should be made at least daily, or more frequently if indicated. It may be necessary to encourage the wombat to move around in order to make a meaningful health assessment.
Transport boxes for wombats need to be strong and well-ventilated. Specially constructed wooden crates with mesh ventilation panels and a sliding door are recommended. A large dog transport crate (plastic and wire) may be suitable in an emergency for a debilitated wombat. Heavy-duty hessian or canvas sacks can be used to hold wombats for short periods only, as animals easily become overheated. Most wombats travel well and do not require sedation (Vogelnest 1999).
4.4 Individual marking and identification
The most common technique used for permanent individual identification of wombats is passive integrated transponders (PIT tags) or microchips. The standard site for insertion of microchips is SC on the dorsal midline between the scapulae. The needle hole should be closed with tissue glue immediately after insertion. Temporary identification methods such as stock mark paints, hair dyes and bleaches have been used. Such methods offer the ability to identify individuals from a distance and are a useful monitoring aid during introductions and field studies (Fig. 9.2).
All wombats are strict herbivores. In the wild they principally graze on native grasses, but also eat roots, fungi, forbs and other bushes when green grass and surface water is not available (Wells 1989). They will also eat introduced grass species. Wombats actively create a ‘lawn’ of fresh green shoots by closely grazing the grasslands in the proximity of their burrow. This allows them to selectively consume high-nutrient high-moisture pastures, in an otherwise low-water and low-nutrient environment (Hume 1999). Generally their wild diet has a low nutrient value. The captive diet should mimic the natural diet as closely as practical.
Captive wombats should be fed high-roughage low-quality palatable hays and native grasses (preferably in clumps with soil attached). Some institutions feed specially formulated high-roughage (15%) low-protein (12.5%) pellets. A small amount of vegetables such as sweetcorn, sweet potato or carrot can be offered. In general, large amounts of vegetables and rich hays such as lucerne and muesli or rolled oats should be avoided as they may lead to bloat, other gastrointestinal diseases and obesity. Wombats should never be fed dog food. In the past, this was a common practice in some institutions. It is believed to be a contributing factor in the development of calcification disorders (Booth 1999) (see 10.6.1b). Wombats in long-term captivity need non-toxic branches or logs to chew on to encourage tooth wear. Water points and food stations are generally suspended (20 cm) off the ground. In temporary situations, heavy ceramic, concrete or metal dishes and bowls may be used. Wombats may destroy or ingest plastic bowls.
An example of a suitable daily ration for a captive wombat is:
- meadow hay and/or oaten hay (ad lib);
- fresh grasses, preferably native (ad lib);
- small amount carrot or sweet potato (200 g);
- fresh cut eucalyptus or wattle branch;
- dried maize (50 g) or fresh sweetcorn (100 g) or cut apple (100 g);
- lucerne hay (fed occasionally, small biscuit only).
Convalescing or debilitated wombats may benefit from a higher-energy diet, with greater quantities of foods such as sweet potato, sweetcorn, carrot, apple and the addition of higher-protein herbivore pellets and judicious amounts of bread. Alterations and additions to diets during convalescence are generally empirical, based on the food preferences and health status of the individual wombat. In all cases, diets should be altered gradually in order to minimise disturbances to gut flora and function. Favoured foods, including bread, may be used as a vehicle to administer oral medications.
Wild adult wombats, especially hairy-nosed wombats, often refuse to eat for days or weeks when first brought into captivity. Freshly cut native grasses may be the only food these animals will recognise or eat. Grated carrot, apple and sweet potato may also tempt reluctant feeders. Due to their low metabolic requirements, wombats (in particular hairy-nosed wombats) appear better able to tolerate extended periods of inappetence or anorexia than other marsupial species. It may be difficult to quantify the energy and fluid needs of the individual and to judge whether dietary intake is inadequate. Body weight fluctuations must be interpreted alongside gut-fill and hydration in inappetant animals, as wombats may dramatically decrease in body weight through decreased gut-fill alone.
On occasion, debilitated wombats have been force-fed (via stomach tube) under general anaesthesia or assist-fed (using a 60 mL syringe placed into the commissure of the mouth) under manual restraint. An energy-rich gruel of marsupial milk replacer powder, pureed vegetables and psyllium husk for additional fibre has been used. Adult anorexic wild-caught southern hairy-nosed wombats have been force-fed under anaesthesia, twice weekly, with 750 mL of the following pureed mix:
- 2 cups soaked kangaroo pellets;
- 200 g sweet potato;
- 2 apples;
- 2 carrots;
- 600 mL oral rehydration solution.
In the author’s opinion, the usefulness of such intervention is debatable as the stress of force-feeding appears to negate the benefits of increased energy and fluid consumption. Diazepam (0.1 mg/kg SC, given daily 30 min before offering food) with or without the addition of vitamin B complex (1 mL/kg SC sid for 3 d) has also been used to stimulate appetite in debilitated and recently captive wombats (R Woods pers. comm.).
6.1 Capture and physical restraint
Wombats are extremely strong animals; their teeth and claws can cause serious injury. Some wombats (usually common wombats) may charge if cornered. All wombats, in particular hand-reared males, may become very aggressive, sometimes without apparent provocation.
Wombats may be physically restrained for very minor procedures or for induction of anaesthesia. Most clinical procedures on adult wombats (e.g. physical examination, blood collection) will require heavy sedation or general anaesthesia.
Wombats in burrows or burrow substitutes can be difficult to access and restrain. Wombats often present their rear end towards the handler as a natural defence mechanism. When restraint is attempted, they may attempt to crush the handler against the roof of the burrow with their rump.
With adequate experience and strength, all wombats, even large adults, can be picked up and held for a few minutes. This is done by approaching the wombat from behind and quickly grasping it just behind the front legs with both arms and lifting it off the ground in a bear hug. The wombat should be held firmly against the handler’s chest (Fig. 9.3). Depending on the procedure, it is often more comfortable if the handler sits down once the animal has been restrained (Vogelnest 1999). Care should be taken when releasing the animal so that it does not have the opportunity to turn around and bite. Once restrained, the animal can then be placed in a sack or transport crate or injected by hand or an anaesthetic mask placed over its face (Fig. 9.5). Some animals can be run into a large open sack for restraint or transport. A blanket thrown over a sick or injured wombat may aid capture.
Wombats are innately trap-shy but have been successfully caught in purpose-built metal cage traps. These traps are usually of a walk-through design, positioned at burrow entrances (Fig. 9.4). Wombats attempting to exit burrows must traverse the trap and trip a wire which releases a slide, so capturing the animal (Horsup 1998).
6.2 Chemical restraint
In adult wombats sedation or anaesthesia is commonly achieved using injectable agents, given by hand, following brief physical restraint. IM injections can be given in the lateral thigh, shoulder or lumbar area. The hard dermal plate over the rump makes it impossible to give injections in this area. Wombats can be darted with injectable anaesthetic agents in the same sites.
Diazepam at 0.5–1.0 mg/kg IM provides adequate sedation for several hours (Booth 1999; Vogelnest 1999). Higher doses may be needed in agitated individuals. Midazolam at 0.5 mg/kg IM provides sedation of shorter duration than diazepam (Booth 1999).
The use of long-acting neuroleptic agents in wombats requires further evaluation and cannot be recommended at this time. Evidence suggests that wombats may be very sensitive to this class of drugs. Fluphenazine decanoate at 2 mg/kg IM used in a captive southern hairy-nosed wombat resulted in profound and prolonged (approximately 4 wk) tranquillisation with inappetence (Taronga Zoo records). A similar response was seen in a recently captured northern hairy-nosed wombat (Western Plains Zoo records).
Anaesthesia in wombats is generally uncomplicated. No pre-anaesthetic fasting is necessary in adult wombats. In milk-dependent juveniles, a minimum 1 hr fasting is recommended (Vogelnest 1999).
The injectable agent of choice in wombats is tiletamine/zolazepam. This can be given by IM injection and is an effective induction agent for all wombat species. Typically, a dose of 2 mg/kg IM provides heavy sedation, with sufficient relaxation to allow minor procedures or to facilitate induction of inhalation anaesthesia via a face mask. A dose of 3–5 mg/kg IM provides light anaesthesia in most captive wombats. Paddling and continued jaw movements may be seen when lower dose rates of tiletamine/zolazepam are used and supplementation with inhalation agents is generally required to achieve surgical anaesthesia. Very agitated wombats may require tiletamine/zolazepam doses as high as 9 mg/kg IM. Tiletamine/zolazepam doses up to 15 mg/kg IM have been used safely in wombats (Evans et al. 1998). Anaesthetic induction is rapid and smooth with good muscle relaxation at higher dose rates. Respiration and heart rate remain unchanged and palpebral, conjunctival and corneal reflexes are maintained (Evans et al. 1998).
The duration of tiletamine/zolazepam anaesthesia is dose-dependent. The more rapid recovery following low dose rates can be useful for field procedures. At higher dose rates recovery may be several hours; during this time animals are unco-ordinated and may paddle and roll. To avoid injury, recovering wombats should be placed in a secure quiet area such as a transport box or darkened den (Booth 1999).
Medetomidine at 0.125 mg/kg plus ketamine at 2 mg/kg IM has been used in common wombats (Woods 1999). Reliability and effect are less optimal than with tiletamine/zolazepam. This combination may be useful when reversibility of anaesthesia is a priority. Alfaxalone at 3–5 mg/kg IM has been used successfully in wombats. The level of anaesthesia achieved is dose-dependent (J Hanger pers. comm.).
Inhalation anaesthesia using isoflurane in oxygen is widely used in wombats. Isoflurane may be used as the primary induction agent (via face mask) for smaller, tractable or sedated animals and is commonly used to supplement tiletamine/zolazepam anaesthesia in all age classes (Fig. 9.5). Halothane has also been safely used in wombats.
Intubation of wombats is difficult due to the narrow gape and dental arcade making visualisation of the glottis difficult. The larynx is also a considerable distance from the oral opening. With the animal in lateral recumbency and an assistant maintaining full extension of the head (using a tie looped around the upper incisors and a fist pressed into the dorsal neck behind the head) a long-bladed laryngoscope can be used to allow visualisation of the glottis. An alternative is to pass a stylet (a urinary catheter can be used) into the trachea via the oral cavity and guide the endotracheal tube over this (Booth 1999). Blind intubation is also possible. The larynx is palpated externally and an assistant extends the head and applies traction to the tongue. The tube is then passed over the base of the tongue until it touches the glottis. The tube is advanced as the animal takes a breath. A cuffied endotracheal tube of 5–7 mm diameter is usually suitable for an adult wombat. In many cases, wombats are maintained on face masks for the duration of anaesthesia.
6.2.3 Anaesthetic monitoring
Normal vital signs for wombats under anaesthesia are heart rate 60–120 bpm, respiratory rate 12–30 bpm and body temperature 32–36.5°C. Femoral and other peripheral pulses are easily palpated. Pulse oximetry probes may be placed on the pouch, penis, cloacal mucosa, lip or tongue although readings may be unreliable.
7 PHYSICAL EXAMINATION
Wherever possible, the physical examination of a wombat should begin with a distant observation of the undisturbed animal. Demeanour, responsiveness, behaviours, signs of disease and relevant environmental conditions should be noted. Although wombats are often active during the early morning and late afternoon hours, a free-ranging wombat seen grazing or moving around in the heat of the day is usually sick.
In most wombats a thorough physical examination will require general anaesthesia. Particular points to note when examining wombats include the following.
- Body condition is determined by assessing muscle and fat coverage of the ribs, pelvis and backbone.
- Gut fill gives an indication of recent feeding and digestion. In the healthy animal the abdomen feels full and doughy. Because of the slow passage time and large volume of the wombat gastrointestinal system, changes in body weight should be assessed in conjunction with gut fill (especially in inappetant animals) (see section 5).
- Hydration is difficult to assess clinically because wombat skin is very thick and inelastic. The oral and conjunctival mucosa appear dry even in a well-hydrated animal.
- Body temperature is taken rectally, via the cloaca. Because of wombats’ very low body temperatures, regular digital thermometers may be inadequate. Mercury thermometers may measure lower temperatures.
- Integument is often unhealthy in appearance, with scarred skin and damaged coat. Ectoparasites are common. Grass seeds, other foreign matter and dried mucus are often found in nostrils and ear canals. Damaged claws and nail beds, sometimes with resultant pedal osteomyelitis, are not uncommon.
- Musculoskeletal injuries and disease can be difficult to detect due to the solid build of wombats. Radiographs are often indicated.
- Oral cavity and dental problems are often seen in wombats due to their continually growing teeth. Thorough oral examination for malocclusion, dental spurs and oral trauma will require general anaesthesia and a long-bladed laryngoscope or transilluminator.
8 CLINICAL PATHOLOGY
8.1 Haematology and biochemistry
8.1.1 Sample collection
Blood collection usually requires sedation or anaesthesia in wombats. Venipuncture sites include the radial, cephalic, brachial, medial metatarsal, caudal tibial, femoral or jugular vein (Booth 1999