The dingo, Canis lupus dingo, is closely related to the domestic dog, Canis lupus familiaris, both being subspecies of the grey wolf, Canis lupus. In general terms, the veterinary management of the dingo is based on that of the domestic dog. This chapter will focus on aspects specific to the dingo.
Dingoes are found wild in Australia and parts of south-east Asia (Corbett 2001). They are thought to have evolved from the Indian wolf, Canis lupus pallipes, 6–10 000 yr ago and probably arrived in Australia about 4000–5000 yr ago with south-east Asian seafarers (Savolainen et al. 2004). The dingo is Australia’s largest terrestrial predator, is distributed over most of the mainland and can be found in diverse environments from tropical to alpine, and coastal to arid inland. However, it has never reached Tasmania. European arrival allowed great increase in dingo numbers due to pastoralism and the use of artesian bores. As a result of dingo predation on livestock a dingo fence was built, that has partly excluded the dingo from the main sheep and cereal-growing areas of south-eastern Australia. The dingo is afforded protection in some parts of its range (e.g. national parks), while in other parts it is considered a pest and, along with other wild dogs, is subject to control measures. Poisoning with 1080 (sodium fluoroacetate) in shallow-buried or helicopter-dropped meat baits is the main method of control. Targeted padded-jaw traps, exclusion fencing, opportunistic shooting and livestock guard dogs are also used (Fleming et al. 2001). Increasing hybridisation with domestic dogs, however, poses the biggest threat to conservation of the dingo (Corbett 2001; Fleming et al. 2001; Woodall et al. 1996) and it has recently been listed as vulnerable on the IUCN Red List of Threatened Species (Corbett 2004).
The dingo is held in zoos and animal parks in Australia and overseas, particularly in Europe and North America. In New South Wales it can be kept as a pet without a licence (Corbett 2004; Davis 2001; Fleming et al. 2001; Oakman 2001). However, dingoes are by nature highly sensitive, wary and elusive. Even when well-socialised with humans they remain independent and unpredictable, and liable to revert to aggressive behaviour when frightened or threatened. For this reason, they do not generally make good pets. Dingoes can live for 12–14 yr in captivity, but rarely live longer than 10 yr in the wild (Corbett 2001).
2 ANATOMY AND PHYSIOLOGY
The dingo is a medium sized short-coated dog with a bushy tail. Average shoulder height is about 60 cm. Body weight ranges from 10–20 kg, with males being heavier than females. Dingoes from arid central Australia tend to be smaller than those from cooler or tropical areas. Skull measurements, body size and coat colour show a cline between tropical, alpine and desert dingoes. Ginger with white points is the predominant coat colour, but black, black and tan, and white dingoes also occur. While these coat colours can occur in domestic dogs and hybrids, patches, sable and brindle patterns are not seen in pure dingoes (Corbett 2001).
Many wild dogs and dingo hybrids are visually indistinguishable from pure dingoes, making differentiating pure dingoes difficult. Dingoes can, however, be differentiated from wild dogs and hybrids by a composite score based on a series of skull measurements. Unfortunately, these are best performed at necropsy (Corbett 2001). In the live animal, microsatellite studies have attempted to distinguish pure dingoes from those that have undergone hybridisation with dogs. Past hybridisation events, particularly recent ones, can be detected by this method but a reliable source of pure dingo DNA, such as pelts collected by early explorers, is needed to make these studies definitive (Wilton 2001).
Dingoes can be classed as pups, juveniles, yearlings or adults based on characteristics of canine teeth (Thomson & Rose 1992). An accurate method of estimating the age of adult dingoes and wild dogs uses pulp cavity as a proportion of tooth width, measured 15 mm from the root tip and averaged over both upper canines. These measurements are made from lateral radiographs and applied to a formula to give an age estimate (Kershaw et al. 2005).
The anatomy of the dingo is essentially identical to that of the domestic dog. There is no evidence of special physiological adaptations to the Australian environment (Newsome & Coman 1989). The dingo does, however, differ from the domestic dog in social behaviour and reproductive pattern.
Wild dingoes are essentially crepuscular, particularly in hotter parts of their range, while captive dingoes are more active during the day. They are generally not nomadic and confine their activity to a home range, which varies in size from less than 20 km2 to more than 100 km2 depending on region and prey abundance (Corbett 2001; Green & Catling 1977; Harden 1978). Dingoes are often seen alone but are usually part of a small flexible socially integrated pack that comes together for breeding or co-operative hunting. Solitary animals are more common where small to medium sized prey such as rodents or rabbits abound, since these are easily caught by one animal. Increasing social cohesion and larger packs form with greater reliance on larger prey such as wallabies and kangaroos (Fleming et al. 2001). Dingoes communicate by scent marking and a variety of howls (Corbett 2001). Barking is rare (Newsome & Coman 1989). Within packs, dingoes display a strong dominance hierarchy between and within sexes. The frequency of aggressive interactions within a pack varies with the pack stability but is generally higher between males; the intensity of these interactions may increase during the breeding season (Corbett 1988). The dominant male and female dingo are generally the only pair to raise offspring. In captivity, it is difficult to establish a stable social group with unrelated animals from different sources. Dingoes are therefore best kept in pairs with their offspring (Jackson 2003). Desexed animals may be kept in groups, but this is not always successful.
In common with most wild canids, dingoes are seasonal breeders and produce one litter each year; domestic dogs and dingo/dog hybrids may have two oestrous periods per year. Most matings take place in April and May, with most births in June or July (Catling et al. 1992; Thomson 1992a). A copulatory tie occurs as in other canids. Behavioural data suggests a pro-oestrus period of 1–2 mo (Thomson 1992a), however, vaginal cytology is more indicative of a 10–12 d pro-oestrus and oestrus (Corbett 2001). Gestation averages 63 d with one to eight pups per litter (average three to five) (Harden 1978; Newsome & Coman 1989). Only a small percentage of females breed in their first year (Corbett 2001). Male dingoes in central Australia show a marked seasonal variation in reproductive parameters. There is an increase in testis weight, prostate weight and semen volume, which peak in April and May. Males from cooler areas of south-east Australia do not show such seasonal changes and are capable of breeding year-round. In response to drought, there is a reduction and delay in reproductive response (Catling et al. 1992). All oestrous females mate (usually with the dominant male) and some become pregnant (Corbett 1988). In a pack, offspring of subordinate females are usually killed by the dominant female—the subordinate females then help to rear her pups. Thus only one litter per pack is raised (Corbett 1988). Whelping takes place in a den using available rocky outcrops, hollow logs or burrow entrances. Preference is shown for elevated sites near water. In addition to the mother, other pack members may regurgitate food for the pups. Pups leave the den at about 8 wk of age and increasingly accompany adults on feeding forays (Thomson 1992a), becoming independent from as early as 4 mo (Corbett 2001). Mortality is highest in recently independent pups that do not remain associated with their parents as subadults (Harden 1978). Captive dingoes may show an increase in intensity of aggression during the breeding season, especially between members of the same sex (Green & Catling 1977), which presents challenges for management.
Individual dingoes can be identified by a combination of visual characteristics, ear tags, ear tattoos or passive integrated transponders (PIT tags). PIT tags are usually implanted under the skin between the scapulae and provide the most reliable permanent form of identification. Ear tags are easily lost during fighting or other trauma and may result in permanent tears and notches in the ear pinna.
5.2 Exhibit design
Exhibit design and holding facilities have been well-described (Jackson 2003). The suggested minimum area for a compatible pair of dingoes is 220 m2 with 6.6 m2per additional animal (EAPA 2003). Fencing should be constructed to prevent dingoes from climbing, jumping or digging their way out. As long as adequate shelter is available, additional heating or cooling is generally not required. A holding area with a den should be available, allowing the dingoes to be held off-exhibit singly or in pairs and to be fed individually. Visual barriers or solid fencing may be needed between enclosures if there is a high level of aggression between animals.
5.3 Hospital housing
Where possible, animals undergoing veterinary treatment should be maintained in their familiar areas. If a dingo’s condition warrants it being taken off-exhibit or isolated from other dingoes, the animal may be restricted to its holding area. This allows continued visual, auditory, olfactory and limited tactile contact with conspecifics. If a serious contagious disease is present or the dingo requires intensive treatment, hospitalisation may be necessary. Removing a dingo from its companions for a prolonged time (as little as 12–24 hr for some individuals) may involve a lengthy reintroduction period to avoid extensive fighting (see 5.4).
Suitable hospital facilities depend on the nature of the dingo and how ill it is. Tame or severely ill animals may be kept in a hospital cage suitable for domestic dogs, though not in a room with other animals. Wild dingoes will need a larger holding pen with a den open on one side. Two adjacent holding pens with a slide between is ideal—the dingo can be moved from one to the other to facilitate cleaning without the handler having to go in with the animal. The enclosure should allow the dingo privacy while still giving access to capture it by hand, net or dart.
5.4 Reintroduction to a group
If prolonged separation cannot be avoided, the animal to be reintroduced should be placed in visual, auditory and olfactory contact with the group while remaining protected from attack. If the dingo is not subject to aggressive advances from group members, it can be allowed access to the group. Reintroduction should take place at the beginning of the day so there is opportunity to watch the group for a long period. Plans should be made to separate animals quickly if fighting occurs. It may be wise to feed the group prior to reintroduction, to avoid food-motivated fighting. In some situations, introduction may occur with a feed so that animals are distracted.
The neuroleptic drug zuclopenthixol dihydrochloride at 3.5 mg/kg PO twice daily was given to a group of dingoes to facilitate reintroduction of an animal. The group and the animal to be introduced were all medicated for 1 wk before and 1 wk after the introduction, which went without incident (Vogelnest 1999).
6.1 Natural diet
Dingoes consume prey items including insects, lizards, rodents, rabbits, birds, macropods, sheep, cattle and horses. Mammals predominate, and small to medium sized macropods and rabbits are particularly important prey species. Domestic stock may be killed by dingoes (Fleming et al. 2001) but do not make a significant contribution to the diet (Corbett 2001). Free-ranging dingoes consume about 7% of their body weight per day in food, which equates to approximately 1 kg per day of prey for an average sized dingo. Dingoes in desert regions require 100 mL/kg/d of water in summer, reducing to 70 mL/kg/d in winter. Lactating bitches require 100 mL/kg/d, though extra fluid is gained by ingesting urine and faeces of pups elicited during licking. It has been suggested that ingested mammalian prey may meet the daily water needs at times of lower requirement (Green & Catling 1977).
6.2 Captive diet
Captive diets should match wild diets in nutritional value, texture and variety. Obesity may become a problem in captive dingoes and food intake should be adjusted to maintain a lean body condition. Food intake of 4–5% of body weight per day is suggested as a guide. Captive diets should be based on whole prey items to maintain dental health and contribute to behavioural enrichment. Whole rabbits or chickens, and kangaroo, beef or horsemeat with hide and bone included are good options. Rabbit carcasses should be frozen for ≥1 wk prior to thawing and feeding out to kill tissue stages of the rabbit tapeworms Taenia pisiformis and T. serialis, since the dingo can act as definitive host. Meaty bones such as shank bones should be offered regularly. Good-quality dry dog food may replace some of the prey items. Dingoes should be fed individually once or twice a day; complete starve days are unnecessary. If a varied and balanced diet is offered, supplements are unnecessary. Where diets are based on meat alone, a calcium supplement will be necessary to correct the calcium: phosphorus ratio, as for domestic dogs. Energy requirements increase by up to 60% during late pregnancy and lactation. Drinking water should be available at all times. Medications may be hidden in items such as unsalted butter or liverwurst, which are generally well-accepted.
7.1 Capture and physical restraint
Due to their unpredictable nature, dingoes that will allow handling should always be muzzled and firmly restrained for examination regardless of temperament. Manual restraint methods do not differ from those for domestic dogs. More tractable dingoes, once muzzled, can be picked up off the ground and examined, treated or injected while being held by the handler. This may also be done with the animal standing on the ground or on a table. Dingoes that will not tolerate handling may be confined to a small pen and caught in a net as they run past. Animal handlers must be experienced, so that the dingo is not chased for a prolonged period prior to capture, as hyperthermia may result. IV or IM anaesthetic agents may be administered through the net or, in the case of IV agents, by withdrawing one hind leg to access the lateral saphenous vein. Care must be taken to restrain the dingo’s head to avoid being bitten during injection and to prevent the animal from traumatising its gums and fracturing teeth on the net. The dingo’s eyes should be covered with a cloth or towel during restraint to minimise visual stimuli. Darting is preferred if facilities and experienced personnel for netting are not available (see 7.2).
Cage traps may be used for semi-habituated animals, though wild dingoes are too wary to enterr (Corbett 2001). As with excessive physical exertion, prolonged time in a trap may lead to hyperthermia. Wild dingoes may be caught with padded foothold traps. One study reported a 10% mortality rate (Thomson 1992b), however, over 100 wild dogs or dingoes have been successfully caught without incident by the following method. The animal is caught in a foothold trap and, as soon as possible, its head is restrained by a person using a dog-catching noose (pole with rope noose at the end). A second handler takes hold of the hind legs and the animal is carried, with trap still attached, to a restraint board. The animal is strapped to the board with three straps (one just anterior to the pelvis, one slightly posterior to the front legs and one over the neck), its head is covered with a cloth and the trap is removed. Dingoes will lie quietly without struggling for procedures such as blood collection, skin biopsy or radio-collaring without requiring sedation (D Jenkins pers. comm.). If chemical restraint is needed for a dingo in a leghold trap, drugs can be administered by hand or pole syringe after noosing or netting.
7.2 Chemical restraint
Chemical restraint agents may be administered via hand-held syringe, pole syringe or dart. Dingoes may be darted using a blowpipe or CO2 powered pistol or rifle. More powerful projectors, such as those that use powder charges, are less suitable. Darts should be air-inject and lightweight with fine short barbless needles, e.g. 20 G ×1“ (0.9 × 24 mm) for blowpipes, 18 G × ¾“ (1.5 × 20 mm) for pistol or rifle, to avoid dart impact injury. The large muscle mass of the thigh is the preferred site for dart injection. The weight of the dart and its velocity at impact both play a part in determining any impact injury. Even lightweight darts fired at high speed may result in broken bones or severe muscle trauma.
As with other carnivores, food and water should be withheld for 12 hr prior to general anaesthesia.
Sedatives and tranquillisers used in domestic dogs would be suitable for use in dingoes. The use of neuroleptic agents other than zuclopenthixol (see 5.4) has not been reported in dingoes. In a hospital situation, acepromazine or diazepam may sedate a dingo sufficiently for intensive treatment.
Dingoes can be anaesthetised using any drug or drug combination at dose rates for domestic dogs, providing they can be safely and correctly administered. IV access may be difficult in less tractable animals, so IM drugs are often more useful. Where drug dose rates are quoted as a range, it is preferable to choose the higher end of the range rather than the lower end to ensure adequate immobilisation, particularly in the field where body weights must be estimated and animals are frequently active or apprehensive. If supplemental doses are required to achieve adequate restraint, an additional half-dose of the primary immobilising agent may be given. In the field, or in captive situations where prompt return to the pack is desirable, use of drugs or drug combinations that can be antagonised is an advantage. This also allows the option of daily immobilisations for treatment with immediate return to the pack, and minimises potential problems associated with prolonged recovery.
IV agents such as propofol, alphaxalone and thiopentone are all suitable for use in dingoes at standard canine dose rates. Tiletamine/zolazepam at 1.5–2 mg/kg IV or 8–10 mg/kg IM is usually sufficient for short procedures or to facilitate intubation. This combination has a wide safety margin and smooth induction and recovery, though recoveries can be prolonged (up to 8 hr) with higher doses. A single dose of 120 mg ketamine and 60 mg xylazine was suggested for immobilisation of wild dingoes (13–18 kg) by helicopter-darting (Thomson 1992a). A standard dose of 0.5 mg etorphine plus 2.5 mg acepromazine was also considered a useful reversible combination for immobilising wild dingoes (Green 1976). Though their use has not been reported in dingoes, ketamine 2.0–5.0 mg/kg with medetomidine 0.04–0.1 mg/kg IM or tiletamine/zolazepam at 1–3 mg/kg combined with 0.03–0.08 mg/kg medetomidine IM provides light to surgical level of anaesthesia in wild canids, depending on the dose (Kreeger 1999; Kennedy-Stoskopf 2003), and could be considered in dingoes. The medetomidine may be reversed using atipamazole at 4 times the medetomidine dose IM. Butorphanol/xylazine can be used on relatively calm captive canids (Kreeger 1992). Dose rates given for grey wolves are 2 mg/kg xylazine and 0.4 mg/kg butorphanol IM, antagonised by naloxone 0.05 mg/kg and yohimbine 0.125 mg/kg IV (Kreeger et al. 1989). These combinations could be considered for use in dingoes.
Whenever a dingo is removed from its pack for more than a few hours, there is the potential for a change in group dynamics and resultant fighting. Even in a relatively stable pack, the animal being reintroduced may be severely injured or killed. Elective procedures should be carefully timed to avoid peak aggression times such as breeding season. Animals should be fully recovered from anaesthetics before being reintroduced. There should be adequate daytime left to observe behaviour of the group, and sufficient staff and facilities to quickly separate animals if serious fighting occurs.
8 CLINICAL PATHOLOGY
Collection and analysis of samples for diagnostic purposes are similar to those used for domestic dogs. Clinical pathology values, including haematology and serum biochemistry, fall within reference ranges for domestic dogs. The morphology of the blood cells in dingoes is similar to those of domestic dogs (Clark 2004) and they share many of the same blood groups (Symons & Bell 1992).
9 REPRODUCTIVE MANAGEMENT
Dingoes breed readily in captivity so assisted reproduction techniques are usually not required. Permanent contraception or injectable or implantable forms of temporary contraception are generally preferred as compliance with oral dosing is often difficult.
9.1 Permanent contraception
In a non-breeding group, it is preferable that all females be ovariohysterectomised and all males castrated to avoid more intense fighting and loss of condition associated with the breeding season. Vasectomy or castration of the male will not prevent potential adverse effects in females from prolonged cyclic exposure to endogenous steroids associated with the obligate hormonal pseudopregnancy that follows ovulation. Elective procedures such as these are best undertaken outside the breeding season. Surgical sterilisation may be performed prior to sexual maturity; this may assist in pack stabilisation although desexed dingoes still fight.
9.2 Temporary contraception
9.2.1 GnRH agonist implants
Deslorelin (Suprelorin®, Peptech Animal Health), a GnRH agonist implant, is considered the safest reversible contraceptive for female canids (AZA Wildlife Contraception Centre 2006