The intelligence of Homo sapiens enabled it to subdue the largest and fiercest of the wild animals and the story of this subjugation is probably as old as the history of human race on the earth. The only difference with the modern time is probably that the primitive man did this in the crude methods of their times and the modern man has fine-tuned the techniques by gathering all the experiences of the past. The availability of the potent stupefying drugs and the precision syringe delivery systems from afar in the past few decades have nearly revolutionized the science and art of restraining wild animals. Restraint varies from confinement in an unnatural enclosure to complete restriction of muscular activity or immobilization (hypokinesis).The elimination of the troublesome wild animal in human context was the <italic>modus operandi</italic> of wild life conservation departments only a hundred years ago. But at the face of rapid industrialization, urbanization and human population explosion after the World War-II, much precious wild life has perished and the remaining few have been pushed into a few pockets in Asia and the African continents. Because of the ever increasing human-animal conflict as the human settlement continues to dig into wild animal habitats, lots of precious wild animals are left injured by the farmers in an attempt to protect their farms. The poachers also leave many wild animals injured while trying to kill and decamp with the meat and/or trophies. Safe restraints of these injured animals for rendering necessary treatment has become a routine work of the wild life veterinarians as every individual animal has become precious at the face of their rapidly dwindling number. Many animals stray deep into human settlements or washed away by the flood and need to be brought back safely. Sometimes a single animal or even an entire population of wild animals isolated in an island or a patch of forest delimited by human settlement has to be immobilized for translocation into a suitable habitat elsewhere. Wild animals also need to be immobilized for biological research, bio-telemetry, rescue of trapped animals, controlling of a rogue and many other such situations.<sec id="sec001"><title>Physical methods of restraints

IJVS

Indian Journal of Veterinary Surgery

0254-4105

Indian Society for Veterinary Surgery

ijvs-26-2-001

RESEARCH NOTE

Restraint and anesthesia in wild animals: A review

Sarma

K.K.

Associate Professor

Department of Surgery and Radiology, College of Veterinary Science Assam Agricultural University, Khanapara, Guwahati-781 022

122005

2627584122004

The intelligence of Homo sapiens enabled it to subdue the largest and fiercest of the wild animals and the story of this subjugation is probably as old as the history of human race on the earth. The only difference with the modern time is probably that the primitive man did this in the crude methods of their times and the modern man has fine-tuned the techniques by gathering all the experiences of the past. The availability of the potent stupefying drugs and the precision syringe delivery systems from afar in the past few decades have nearly revolutionized the science and art of restraining wild animals. Restraint varies from confinement in an unnatural enclosure to complete restriction of muscular activity or immobilization (hypokinesis).The elimination of the troublesome wild animal in human context was the <italic>modus operandi</italic> of wild life conservation departments only a hundred years ago. But at the face of rapid industrialization, urbanization and human population explosion after the World War-II, much precious wild life has perished and the remaining few have been pushed into a few pockets in Asia and the African continents. Because of the ever increasing human-animal conflict as the human settlement continues to dig into wild animal habitats, lots of precious wild animals are left injured by the farmers in an attempt to protect their farms. The poachers also leave many wild animals injured while trying to kill and decamp with the meat and/or trophies. Safe restraints of these injured animals for rendering necessary treatment has become a routine work of the wild life veterinarians as every individual animal has become precious at the face of their rapidly dwindling number. Many animals stray deep into human settlements or washed away by the flood and need to be brought back safely. Sometimes a single animal or even an entire population of wild animals isolated in an island or a patch of forest delimited by human settlement has to be immobilized for translocation into a suitable habitat elsewhere. Wild animals also need to be immobilized for biological research, bio-telemetry, rescue of trapped animals, controlling of a rogue and many other such situations.<sec id="sec001"><title>Physical methods of restraints

There is plenty of literature giving exhaustive account of the physical methods of restraining wild animals. Bateman (1971; 1979) has presented vivid details of the ancient and the modern physical methods of trapping fish, birds and mammals. The ancient India invented many methods for trapping and catching wild animals and a very detailed account of various methods used for the purpose by the aborigines are available (Kirkpatrick, 1954). The common langoors were caught by trap nets, tigers and panthers were trapped and killed ingeniously and smaller mammals were easily foxed into booby traps laid using the traditional knowledge about their behaviour. The elephant capture techniques are still in practice in large parts of Asia, though the sheer traditional artistry of subduing the largest terrestrial mammal by physical means is in a rapid decline due to the official restrictions on capture. Stracey (1969) has given a detailed account of various methods adopted by the people of different geographical areas like the Kraal method of Myanmar, pit method of South India, noosing techniques of Assam, Nepal, Indonesia and the Kheda method adopted by the British in Myanmar and India for capturing wild elephants. Barua (1996) elaborated on the elephant capturing techniques of North-East India. Fowler (1974; 1978) reviewed the various rope works and physical restraint techniques of wild and captive animals. Schmidt (1986) outlined the various physical and chemical restraint techniques of captive elephants.

Baring the elephants, bear, monkeys and some birds, which were captured for domestication either for work, play or amusements, most of the other animals were captured for meat till the beginning of the 18^th century. Later, some people observed the crowd pulling potentials of caged wild animals and performing wild animals in the circuses and zoos, and hence large-scale captures were performed in their habitats. The traditional restraint devices were modified suitably by applying modern technical expertises. Fortunately, the chemical capture techniques have developed rapidly in the second half of the 20^th century making the restraint operations easier and safer. But owing to the difficulties of physically darting some smaller, sensitive and elusive wild animals, people are still adopting the physical restraint techniques to capture some of the free rangingwild animals (Larsen, 1967; Ramsey, 1968; Jones, 1984), which are later supplemented with suitable anaesthetic drugs, whenever required. Physical restraint can suitably be used along with chemical agents even in the larger wild mammals.

Neuromuscular blocking (NMB) drugs

Crude curare muscle relaxants of plant origin and delivered by crossbow arrows were probably the earliest chemical immobilizing agents used by mankind to restrain big wild game. The ancient African tribes discovered this "miracle herbal" powers to subdue big wild animals to kill them later for food. Despite their long history of use, NMB drugs are generally inferior to modern drugs. Two major disadvantages of these drugs include very low therapeutic index and dosage errors of only 10% can result in either no effect or death (IWVS, 1992). Mortality rates as high as 70% have occurred. The second disadvantage is that these drugs are unable to cross the blood brain barrier and have no central nervous system effects and do not affect the level of consciousness. However, advantages of the NMB drugs are that they are generally very fast acting (3–5 min) and their action is short lived (15–30 min) (Kreeger, 1999).

The depolarizing muscle relaxants are typified by succinylcholine chloride that acts by depolarizing the motor endplate and disrupting impulse transmission to the skeletal muscles. Other similar drugs like suxamethonium and decamethonium have also been used. These drugs produce only relaxation but no unconsciousness nor analgesia. Therefore, this group of drugs while being efficient in restraining the wild animals, produce severe psychological stress in the fully awake wild animals leading to death and other complications subsequently due to shock. The animals may be affected by psychological, auditory and even visual stimulations. Cessation of respiration is a natural result of succinylcholine chloride immobilization. Therefore, procedures should not be attempted without resuscitation equipment ready in hands (Fowler, 1978). These drugs also produce tachycardia and elevated blood pressure. Moreover, there is no specific antidote to reverse the effects of these drugs. There are several reports of use of depolarizing muscle relaxants in wild animals, particularly in the deer species (Pistey and Wright, 1961; Harthoorn, 1965, 1973, 1976; Miller, 1968; Allen, 1970; Jacobson et al., 1976; Amstrup and Segerstorm, 1981), alligator and crocodiles (Klide and Klen, 1973; Messel and Stephens,1980) but is not favoured any more due to low margin of safety and lack of sedative and analgesic properties.

Gallamine is a phenolic ether with quarternary ammonium groups, similar in its action to curare, which raises the threshold for depolarization of the motor end plate by acetylcholine. It has been successfully used for the immobilization of crocodile (Crocodylus niloticus) mainly in Zimbabwe (Loveridge and Blake, 1972; Loveridge, 1979). The researchers found gallamine to be a safe anaesthetic agent for the crocodiles for its wide therapeutic index with doses ranging from 0.64 to 7.74 mg/kg, i.m. No undue bradycardia or respiratory impairment was evident following its administration. Neostigmine methyl sulphate (0.03–0.06 mg/kg) was found to be a good antidote to gallamine.

Opioids

The early history of opioid use in medicine involved opium, the first known analgesic, which has been used for over 2,000 years. It is probable that the first chemists who discussed drug immobilization techniques were prehistoric hunters (Hofmeyr, 1973; Van der Walt, 1973). Administration on a scientific basis was only possible after Serturner isolated the active principle, which he called morphicum (Snyder, 1977; Janssen, 1981; Vigeura, 1986). The first investigation of the use on morphine for premedication was probably made by Bernard in 1869 (Haigh, 1990); by 1872, morphine was administered by subcutaneous injection for minor surgery. In 1900, a combination of morphine and scopolamine was used by Schneiderlein as a general anaesthetic. The technique caused several deaths and was soon abandoned.

Various morphine derivatives were introduced in the beginning of 20^th century and the first entirely synthetic opiate, pethidine, was introduced in 1933. The first opiate antagonist, nalorphine was not introduced until 1951. In last 40 years or so, several extremely potent opioids have been investigated. One of these was f entanyl. The most potent of the opioids described to date is carfentanil. The first reports of a synthetic opioid for animal capture described the use of diethyl-thiambutene for the capture of African ungulates (Harthoorn, 1962; Hungerford, 1988). The dose required for an adult rhinoceros was about 20 mL.

Later, reports on the oripavine derivative etorphine HCl, which had been tested in several species were published (Beeman et al., 1974; Bongso and Perera, 1978). The quantity of this drug required for immobilization of large herbivores was very low and the availability of etorphine (M₉₉) in the seventies has revolutionized the field of chemical restraint of wild animals (Haigh, 1979; Harthoorn, 1967; Harthoorn, 1973; Harthoorn, 1976; Harthoorn and Bligh, 1965; Pienaar, 1969; Woolf, 1970). Etorphine hydrochloride is still the drug of choice for immobilizing many large wild mammals like elephant, rhinoceros, tapir and zebra (Boever, 1987). We have observed that no drug is in fact capable of immobilizing rhinoceros (Rhinoceros unicornis) other than an opioid. Explanations of the great potency of etorphine relative to other opioids centre on its molecular structure and lipophilia. The structure of etorphine molecule increases its affinity for the receptors 20 times more than that of morphine and itslipophilia is also 300 times as greater, and hence more efficient in crossing the blood brain barrier (Snyder, 1977; Bongso and Perera, 1978).

Approximately concurrent with the development of etorphine, fentanyl was synthesized and introduced for wild animal capture (Harthoorn, 1976; Janssen, 1981). Fentanyl is a 4-amino-piperidine derivative first synthesized in 1960. This drug has been extensively used in Africa (Keep, 1973; Pienaar, 1969; 1973; Haigh, 1976, 1977; Harthoorn, 1976; Haigh et al., 1983). One of the principal advantages of fentanyl is that many species immobilized with it remain standing (Haigh et al., 1977), which is particularly useful for animals caught for translocation and placed directly in crates. Combination of fentanyl and etorphine has the advantage of a more rapid induction than when used alone. The dose of antagonist required for reversal was also less (Keep, 1973; Patenaude, 1979).

Around 1970, carfentanil citrate was synthesized (Janssen, 1981). It is also a 4-amino-piperidine derivative and is the most potent opioid known (Wallach et al., 1967; de Vos, 1978). It is effective at a very low dose of 1 µg/kg for some species (Haigh et al., 1983). One problem with this drug is that successful reversal requires substantially higher doses of antagonist than any other agonist tested (de Vos, 1978; Franzman et al. 1984; Weisner et al., 1984; Joseph and Cornell, 1987).

The latest opioid to be described in the context of wildlife immobilization is another 4-amino-piperidine derivative, A3080, which appears to have about half the potency of carfentanil but is extremely safe and fast acting (Janssen et al., 1991, 1993). Several animals recovered without being given a reversal agent.

Limited overdosing with opioids is generally safer than underdosing. The excitement, struggle and resultant overheating seen in the induction phase is much reduced or eliminated at higher doses, providing less opportunity for the animal to overheat and develop capture myopathy or heat stress (Pienaar, 1969; Miller and Will, 1974; Harthoorn, 1976).

A number of drugs with synergistic interaction have been used to improve the quality of immobilization with opioids. In particular, hyaluronidase has been used for speeding induction (Woolf et al., 1973; Haigh, 1979; Franzman, 1982; Osofsky, 1995). The three main classes of neuroleptic drugs that have been used to enhance opioid effects are the phenothiazine derivatives (acepromazine), the butyrophenones (droperidol) and the á₂-adrenoceptor agonists (xylazine).

Acepromazine with etorphine (Immobilon) has been the most widely used immobilizing combination for the large ungulates in Africa and Asia (Harthoorn, 1967, 1976; Bongso and Perera, 1978, Bristol et al., 1984; Sarma, 2002). Garcia et al. (1996) observed excellent immobilization of free ranging Baird's Tapir (Tapirus bairdii) with 1.88 mg of etorphine and 7.7mg of acepromazine. The acepromazine permitted a 63% reduction in etorphine dose and shortened induction time. In equidae, acepromazine has been shown to ameliorate some of the hypertensive effects of etorphine. But phenothiazines are not without risks. They have been incriminated in extrapyramidal effects, such as torticollis and fatal disturbance of heat regulation (Harthoorn, 1965; 1976; Pienaar, 1969; Jones, 1972; Hebert and McFetridge, 1976; Tobey and Ballard, 1985; Fletcher, 1986; Blumer, 1991). Acepromazine being a phenothiazine derivative was found to induce severe photosensitization in elephants (Cheeran et al., 2002).

The butyrophenones have also been used widely as synergists with opioids. The group includes azaperone, fluanisone, droperidol and haloperidol. This mixing reduces both total dose requirements and induction time (Marsboom, 1969; Haigh et al., 1983). Some advantages of azaperone over the phenothiazines include a lack of effect on thermoregulation. Fentanyl when mixed with Azaperone, produced excellent immobilization in sea otters (Williams and Kocher, 1978; Williams et al., 1981). Fentanyl citrate forms a very popular neuroleptanalgesic combination Innovar-Vet with droperidol (each mL containing 0.4 mg sublimaze-fentanyl and 20 mg inaspine-droperidol). Two mL of fentanyl immobilized an Indian wild dog within one minute of injection that recovered spontaneously in an hour (Kotwal, 1981). Unlike morphine, Innovar-Vet does not usually cause vomition in canidae. The drug combination induces a typical condition where the animal is unconcerned with regards to the environment although it is not asleep, nor is it alert. Administration to monkeys at 1 mg/kg produced profound psychomotor sedation and complete analgesia (Field et al., 1966). Extensive series of experiments with fentanyl have been conducted on wild African ungulates (Pienaar, 1968). Treatment in case of adverse reaction to fentanyl consists principally of atropine administration to counteract a depressant effect on the heart (Harthoorn, 1976). The effects of fentanyl may be reversed with the usual morphine antagonists such as nalorphine, naloxone and levallorphan, which do not of course reverse the effects of the tranquillizer present in the combination.

The á₂-adrenoceptor agonists, particularly xylazine, have been widely used as part of opioid-based mixtures for immobilization of a variety of ungulates (Harthoorn, 1973, 1976; Bush et al., 1976; de Vos, 1978; Haigh, 1977, 1978; Franzman, 1982; Machado et al., 1983; Franzman et al., 1984; Jessup et al., 1984, Kock and Berger, 1987). For Giraffes, the addition of xylazine produced the best results in a series of trials of different combinations based on carfentanil (Bush and de Vos, 1987). In etorphine/xylazine mixtures, xylazine dose of 1mg/kg was associated with prolonged recovery periods in moose, whereas in the same study, dose of 0.6 mg/kg did not have the same effect (Franzman andArneson, 1974). Xylazine added to carfentanil for the immobilization of mule deer (Odocoileus hemionus) caused prolonged and pronounced post-recovery sedation. This problem was mitigated by lowering the dose of xylazine in the mixture from 1 mg/kg to 0.6 mg/kg b.wt (Jessup et al., 1984). In another experiment, Delvaux et al. (1999) observed that carfentanil/xylazine combination was better when compared to succinylcholine and xylazine as single agents in the free ranging moose (Alces alces). Scimitar horned oryx (Oryx tao) could not be immobilized without xylazine in the mixture with opioids (Kock and Pearce, 1985), and in the related Arabian oryx (Oryx leucoryx), xylazine eliminated the extreme excitement seen during induction with either etorphine alone or in combination with acepromazine (Machado et al., 1983). Xylazine also eliminated side effects of etorphine immobilization in pygmy hippopotamus (Pearce et al., 1985).

On rare occasions, diazepam was also used alongwith the opioids. Williams and Kocher (1978) observed that etorphine @0.75 mg per adult sea otter along with diazepam @1.25 mg/kg b.wt met most of the requirements for field anaesthesia of the species. Pusateri et al. (1982), however, cautioned against combining diazepam with other aqueous preparations.

Opioid antagonists

Perhaps the biggest advancement in wildlife management techniques in the last 40 years has been the development of agonist and antagonist opioids, which enabled the wildlife veterinarian the opportunity to control the immobilization according to the length of the procedures. There are several antagonists for use and all the antagonists so far developed for use in animals are derived from the basic phenanthrene structure that is similar to that of thebaine. Interestingly, few of the drugs used initially as opioid antagonists namely, nalorphine and levallorphan have agonistic effects as well, and considerable care has to be exercised in their use, especially if repeat doses are to be given (Harthoorn,1976; Summerhays,1976; Weisner et al., 1984). Diprenorphine was much faster than levallorphan as antagonist to carfentanil in red deer, moose, andmouflon (Ovis musimon). Both diprenorphine and cyprenorphine were developed more or less at the same time as etorphine. Diprenorphine has become the major antagonist for etorphine in majority of the countries except in South Africa, where both the antagonists are still used extensively (Haigh, 1990). In some circumstances, nalorphine was preferred to cyprenorphine because it produced a more thorough and complete reversal of narcosis (Hofmeyr, 1974).

Naloxone is a highly specific opioid antagonist with almost no agonistic properties. It has become widely used drug for the reversal of all of the immobilizing opioids (Beeman et al., 1974; de Vos, 1978; Higgins and Kock, 1984). Naloxone has been reported to have a very short half-life, which is a major drawback of the drug (Pace et al., 1979; Bryson, 1989). Naltrexone is another specific opioid antagonist that is characterized by a long half-life.

Alpha-2 adrenoceptor agonists

Xylazine, the first drug of this non-narcotic group of compounds is a thiazine derivative. Since the development of xylazine in the late 1960's, it has been extensively used in nondomestic animal immobilization as the sole agent or in combination with cyclohexosamines or opioids, to improve the quality of the chemical immobilization. Xylazine is a potent α₂-adrenergic agonist. It acts upon the CNS by activation of α-adrenoceptors; this increases sympathetic discharge and reduces release of norepinephrine. Through the central stimulation of α₂ adrenergic receptors, xylazine has potent antinociceptive activity, in addition xylazine has α₁ adrenergic effects; eliciting both central and peripheral action upon these adrenergic receptor subtypes. Xylazine also produces skeletal muscle relaxation by inhibition of intraneuronal transmission of impulses at the level of CNS. Because of its potency, ease of handling and high margin of safety, xylazine attracted the veterinary professionals, which prompted its application in wide range of domestic and wild animal species. The drug was used in numerous wild species with fairly good results (York and Huggins, 1972; Young and Whyte, 1973; Shmidl, 1974; Roughton,1975; Schmidt, 1975; Bongso, 1979; Raptopoulos and Weaver, 1984; Trembath, 1985; Pathak et al., 1990; Ranganath et al., 1993; Sarma and Dutta, 1996, 1997; Sarma, 1999, 2003; Sarma et al., 1997; Sarma and Pathak, 2001).

Xylazine hydrochloride produces standing sedation with an average induction period of 25–30 min in elephants. Stimulation during inductionstage may delay or prevent optimum sedation (Sarma, 1994). When subjected to a too-rapid approach, a seemingly sedated animal may rouse explosively, jeopardizing the safety of the operators (Fowler, 1978). The drug can be administered in both i.m. as well as i.v. routes. There is wide species variation in the optimum dosage. Immobilization occurs in 3–5 min following i.v. and 25–30 min after i.m. administrations. Though the sedation and relaxations persists for 1–2 h, analgesia is short-lived and does not last for over 30 min, hence no painful procedure should be performed after 30 min and some physical restrain should also be applied while handling an animal immobilized with xylazine. Rhinos (Rhinoceros unicornis) could not be satisfactorily immobilized even with very high doses of xylazine (Sarma et al., 1997). Occasionally, elephants behave erratically following administration of xylazine (Sarma, 1999).

Muscle tremor, apnoea, respiratory depression, bradycardia and partial A-V block occasionally occur at standard doses of xylazine (Clark et al., 1982; Kolataand Rawlings, 1982). Explosive response to stimuli can result in injury (Knight, 1980), therefore, waiting 5–10 min after an animal goes down is advisable before it is approached slowly and quietly. Depression of thermoregulation and significant hyperglycaemia are some other common hazards of xylazine sedation (Sarma, 1994). Xylazine HCl produces additive effects when combined with tranquillizers and barbiturates (Cronin et al., 1983), therefore when the drugs are to be combined, dosages should be reduced and caution should be exercised (Karesh et al., 1986).

Xylazine HCl can be used for mild sedation to complete immobilization (Bauditz, 1972). Xylazine in combination with ketamine provides excellent immobilization of bears, wolves (Ballard et al., 1982, Kreeger et al., 1986), sloth bear (Murthy et al., 2004), wild monkeys (Maiti et al., 2004), Asian elephants (Elephus maximus) (Sarma, 1994), captive blue bulls (Boselephus tragocamelus) (Sarma et al., 1997), Asiatic lions (Kumar, 2004), Smooth-coated otter (Hussain et al., 1996), Chital (Axis axis), tiger, leopard, hyena, and sambar (Dhoot et al., 2004) and many other non-domestic species of animals. Combination with ketamine was found to mitigate a few undesirable side effects of xylazine in elephants (Sarma, 1994).

Yohimbine (Jessup et al., 1983; Jacobson and Kollias, 1984; Ramsay et al., 1985; Kreeger and Seal, 1986; Sarma, 1994), doxapram (MacKintosh and Van Reenen, 1984; Hatch et al., 1985; Hsu et al., 1985), 4-aminopyridine and tolazoline (Kreeger et al., 1986) have been used successfully for reversal of xylazine induced sedation in different non-domestic animals.

Medetomidine is another α₂- adrenoceptor agonist that has become popular in wild animal anaesthesia. Medetomidine acts by modulating nor-adrenaline release at adrenergic nerve terminals. Alone, it induces sedation, which is dose dependant (Jalanka, 1991). The extent of sedation and analgesia are controlled by the dosage at lower levels but after attaining an optimal level of sedation, additional dosages influence only the duration of the effect (Short, 1992). Medetomidine is reported to be 30 times as potent as xylazine (Jalanka, 1989). The drug has a wide margin of safety and is reported to have no untoward effects on pregnancy (Jalanka and Roeken, 1990). Vie and Thoisy (1996) used medetomidine i.m. (0.15mg/kg) alongwith ketamine (4 mg/kg) in Red Howler monkeys (Alouatta seniculus) that produced excellent anaesthesia. Medetomidine has been proved to be a very useful and safe anaesthetic in the deer species in combination with other drugs like ketamine and tiletamine (Moran and Peinado, 1996). Caulkett et al. (1996a) has standardized the immobilizing dose of medetomidine-ketamine and its reversal with atipamezole in free ranging woodland Caribou (Rangifer tarandus caribou) and described it as a safe and effective immobilizing combination for the species. Caulkett et al. (1996b) also evaluated medetomidine in respect of its cardiopulmonary effects in polar bear (Ursus maritimus). Cattet et al. (1997) reported the use of medetomidine along with zolazepam and tiletamine in polar bear. Haulena et al. (2000) safely used medetomidine 140 µg/kg and 2.5 mg/kg ketamine combined in Californea sea lions (Zalophus californianus). Medetomidine has also been found to be very useful at a low dose of 5 µg/kg b. wt for anaesthetizing both free ranging and captive Asian elephants (Sarma, 2001; Sarma et al., 2002). The high therapeutic index, rapid and smooth induction, relaxation of the trunk, and smooth and spontaneous recoveries were some of the highlights of medetomidine anaesthesia in elephants. The ability of the elephant to remain standing during deep sedation with medetomidine was a major advantage. Atipamezole was the drug of choice for reversal of medetomidine-induced sedation in all the animals. Virtanen and MacDonald (1987) and Kreeger (1999) observed that atipamezole promises to be the drug of choice for antagonizing anaesthesia induced by any a₂-adrenoceptor agonists, particularly medetomidine, because it can effectively antagonize the behavioural, cardiovascular, gastrointestinal, neurochemical and hypothermic effects of medetomidine.

Dissociative agents

Phencyclidine and its derivatives are called "dissociative agents", because they disrupt communications between various sections of the CNS, with combined stimulations and depressions. The predominant manifestation is determined by species and dosage (Fowler, 1978). Muscle relaxation is poor and in some cases it actually produces excessive muscle tone. Phencyclidine hydrochloride has been extensively used in nonhuman primates and carnivores. Ketamine hydrochloride, its newer analogue has replaced phencyclidine hydrochloride, except when small volumes are required to dart large carnivores and primates. It is also a desirable agent when prolonged immobilization is necessary. Doses vary from 0.5 to 2mg/kg b. wt. The onset of anaesthesia is seen in 15–20 min and immobilization lasts from 1 to 2 h, but the animal remains depressed for 5–48 h (Sarma et al., 1993).

Ketamine HCl, a derivative of phencyclidine HCl is extensively used in wild animal immobilization in combination with various other agents. The animal usually retains normal pharyngeal-laryngeal reflexes that preclude the fear of regurgitation and aspiration pneumonia, but the animal can not be intubated when ketamine HCl is used alone. Ketamine does not produce skeletal muscle relaxation but produces profound analgesia except in the peritoneum (Beck et al., 1971). Ketamine crosses the placental barrier in all species but is not known to cause abortion when used in pregnant animals (Harthoorn, 1976).Ketamine produces tono-clonic convulsions in a small percentage of wild felids. Convulsive effects can be obviated by administering diazepam (0.25–0.5 mg/ kg) with ketamine. Acepromazine maleate is often used in combination with ketamine. Acepromazine decreases catatonia and provides better muscle relaxation (Fazekas et al., 1957, Hankoff et al., 1957).

Tiletamine HCl and zolazepam HCl combined to produce a non-narcotic, non-barbiturate, injectable anaesthestic. True to its group characteristics, tiletamine HCl produces profound analgesia and cataleptoid anaesthesia characterized by rapid induction, and normal pharyngeal and laryngeal reflexes. When it is combined with zolazepam HCl, good muscle relaxation is attained. Low doses produce tranquil state, permitting or expediting procedures not requiring complete anaesthesia. Higher doses are required for excited animals (Kaufman and Hahnenberger, 1975, Taylor et al., 1989). This combination has a wide dose variation depending on species (Schobert, 1987).

First sign of induction appear 2–6 min after injection and immobilization is complete in 5–10 min. Downtime and recovery times are variable among species. Immobilization time is usually 30–60 min, but full recovery may require up to 5 hr. During induction, motor paralysis proceeds from the rear limbs to the f orelimbs (Clausen et al., 1984), which is reversed upon recovery. The drug combination often induces irregular breathing pattern, which may be stabilized by administering doxapram (Hsu et al., 1985). Administration of doxapram may significantly shorten arousal time, but it should be used only when absolutely necessary because doxapram HCl is a powerful stimulant that increases oxygen requirements of tissues and can produce brain damage or even death. Mild to severe ataxia may occur. Hypothermia may occur if prolonged, deep anaesthesia is maintained during cold weather. Doxapram HCl may shorten the arousal time (Hatch et al., 1984, 1985; Hsu et al., 1985), but arousal may be brief.

The combination of tiletamine HCl and zolazepam HCl has a wide margin of safety in a variety of species. This combination is especially suited for the larger carnivores (Haigh et al., 1985, Taylor et al., 1989, Kreeger et al., 1990, Sarma, 2002). Telazol 3.3 mg/kg in combination with xylazine 1.6 mg/kg has been used in 144 wild pigs (Sus scrofa) by Sweltzer et al. (1997); although recovery was prolonged, the combination was credited to be safe and effective for the species.

Conclusions

The wildlife immobilization and restraint has developed into a specialized branch of veterinary medicine in the recent decades. Chemical restraint is the pre-requisite for the handling of wild animal and, therefore, has become the mainstay of the wildlife healthcare programme. Scientists have been using one or the other drug or their combinations for any given species. The wildlife veterinarian is much disadvantaged and often handicapped due to diversity in wildlife fauna without even knowing the exact body weight or health status of the animal to be immobilized, not to speak of any specialized pre-anaesthetic evaluation. Therefore, it is extremely essential to have stupefying drugs with very wide margin of safety and with efficient reversal agents.

Species specificity and dose variations are other big problems with wildlife immobilization procedures.

The search for the best and ideal drug that can satisfy all the requirements in the restrain and immobilization of wild animal is on and will continue as no single drug can fulfill the requirements of sedation, muscle relaxation and analgesia on its own and need to be combined with other agents. Moreover, the craft of drug delivery is equally important, as only efficient delivery mechanism can ensure complete and prompt administration while ensuring safety of the sniper.

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