F:\ALCES\Vol_39\p65\3926.PDF ALCES VOL. 39, 2003 ARNEMO ET AL. – IMMOBILIZATION OF MOOSE 243 CHEMICAL IMMOBILIZATION OF FREE-RANGING MOOSE Jon M. Arnemo1,2, Terry J. Kreeger3, and Timo Soveri4 1Department of Arctic Veterinary Medicine, The Norwegian School of Veterinary Science, NO-9292 Tromsø, Norway; 2Department of Forestry and Wilderness Management, Hedmark University College, Evenstad, NO-2480 Koppang, Norway; 3Wyoming Game and Fish Department, 2362 Highway 34, Wheatland, Wyoming 82201, USA; 4Department of Clinical Veterinary Medicine, Faculty of Veterinary Medicine, University of Helsinki, FI-04920 Saarentaus, Finland ABSTRACT: A wide range of drugs and drug combinations have been used to capture free-ranging moose (Alces alces). Currently, potent opioids are considered the drugs of choice for capture of free-ranging moose. Recommended doses are carfentanil at 0.01 mg/kg or etorphine at 7.5 mg/adult. Combining an opioid with a sedative drug like xylazine will increase the risk of bloat, regurgitation, and aspiration of rumen contents. Extreme toxicity for humans and lost darts are major concerns when using potent opioids under field conditions. The best non-opioid alternative is medetomidine at 40-50 mg/adult combined with ketamine at 600 mg/adult. Carfentanil, etorphine, and medetomidine- ketamine have wide safety margins in moose and the risk of severe anesthetic side effects in healthy animals is minimal. Chemical immobilization from a helicopter in winter is considered the best capture method for moose. Due to animal welfare considerations and a low therapeutic index, neuromuscular blocking agents should not be used in moose. A mortality rate greater than 2% during immobilization and a one month post capture period is not acceptable for routine moose captures. ALCES VOL. 39: 243-253 (2003) Key words: Alces alces, anesthesia, capture, carfentanil, etorphine, immobilization, ketamine, medetomidine, xylazine Free-ranging moose (Alces alces) are chemically immobilized for various research and management purposes: radiotransmitter deployment, collection of biological materi- als, morphometry, health examination, and translocation. Most moose are approached with a helicopter or occasionally by snowmobile, all-terrain vehicle, car, boat, or on foot, and drugs are administered by projectile darts fired from a dart gun. The first chemical immobilization of free-rang- ing moose was carried out in Alaska in 1957-58 with nicotine, a neuromuscular blocking (NMB) agent (Rausch and Ritcey 1961). Since then a wide range of drugs and drug combinations have been used to cap- ture free-ranging moose in North America and Europe, including other NMB agents, tranquilizers, sedatives, and anesthetics. Franzmann (1982, 1998) has published ex- cellent reviews of moose chemical immobi- lization. Here we present an update on recommended drugs, doses, and methods for chemical capture of free-ranging moose. CHEMICAL CAPTURE VERSUS NET-GUNNING Although helicopter net-gunning has been successfully used on moose, with an immediate capture mortality rate of less than 1% (Carpenter and Innes 1995), mor- tality rates as high as 14% have been re- ported from other projects using this method (Olterman et al. 1994). There is no doubt that helicopter net-gunning is a useful method for capture of free-ranging ungu- lates, and in some species it is even consid- ered to be better than chemical immobiliza- tion (Kock et al. 1987a,b,c). In moose, however, we are not aware of a single IMMOBILIZATION OF MOOSE – ARNEMO ET AL. ALCES VOL. 39, 2003 244 publication on stress physiology or possible long-term negative effects (e.g., exertional myopathy, increased risk of predation, re- duced calving success, and reduced sur- vival of offspring) after capture by helicop- ter net-gunning. Whether net-gunning is an acceptable method for moose capture re- mains to be documented. IMMOBILIZING DRUGS There are three major groups of drugs currently used for wildlife capture: Alpha-2 adrenoceptor agonists, opioid agonists, and cyclohexanes (Kreeger et al. 2002). The NMB agents are a fourth group that was extensively used during the pioneer days of chemical immobilization. NMB drugs cause muscular paralysis but the animal is con- scious, aware of its surroundings and fully sensory, and can feel pain and experience psychogenic stress. Due to a very narrow range between effective immobilizing doses and lethal doses, mortality rates as high as 70% have occurred with NMB agents (Kreeger et al. 2002). Although inferior to modern immobilizing drugs, the NMB agent succinylcholine has been used for moose capture in recent years (Delvaux et al. 1999). However, the reported mortality rate due to respiratory paralysis was 7% and only 63% of the immobilization attempts were successful. Due to animal welfare considerations and the low therapeutic in- dex (effective dose:lethal dose), succinyl- choline or other NMB agents should not be used for moose immobilization. Alpha-2 adrenoceptor agonists include xylazine, romifidine, detomidine, and medetomidine. These agents induce dose- dependent sedation and analgesia and they have anxiolytic and muscle relaxing proper- ties. The difference in potency between the alpha-2 agonists is species dependent, but no controlled studies have been done in moose or other wildlife species. In sheep, the equipotent sedative doses (mg/kg) for xylazine, romifidine, detomidine, and medetomidine are 0.15, 0.05, 0.03, and 0.01, respectively (Kreeger et al. 2002). Al- though these drugs may induce deep seda- tion and immobilization in large doses, sud- den arousal may occur. In highly excited animals, induction times are usually pro- longed and immobilization may be impossi- ble regardless of the dose administered. Alpha-2 agonists should therefore never be used as the sole agent for capture of free- ranging moose. They are, however, very useful in combination with opioids or cyclohexanes. Alpha-2 agonists have the ability to potentiate other CNS-drugs; e.g., if ketamine is combined with medetomidine the effective anesthetic dose of ketamine is reduced by as much as 75% in some species (Jalanka and Roken 1990). The effects of alpha-2 agonists can be rapidly and perma- nently reversed by atipamezole, a potent and specific alpha-2 adrenoceptor antago- nist (Kreeger et al. 2002). Other less specific reversal agents, such as yohimbine and tolazoline, can be used to antagonize xylazine, the least potent of the alpha-2 agonists. Opioid agonists used for wildlife immo- bilization include carfentanil, etorphine, fen- tanyl, and, to some extent, thiafentanil and sufentanil (Kreeger et al. 2002). In moose and other cervids, carfentanil (North America) and etorphine (Europe) have been the primary opioids, either alone or in com- bination with xylazine (Kreeger et al. 2002). Carfentanil and etorphine both have high therapeutic indices in moose; i.e., the same dose can be used in most adults regardless of body weight. Underdosing with opioids may cause excitement and hyperthermia and overdosing is therefore considered to be better than underdosing. Although not a “new” agent for wildlife captures (Stanley et al. 1988, 1989), thiafentanil (formerly identified as A-3080) is still an investigational drug for wild animal capture (Citino et al. ALCES VOL. 39, 2003 ARNEMO ET AL. – IMMOBILIZATION OF MOOSE 245 2001, Grobler et al. 2001, Kreeger et al. 2001, Citino et al. 2002). The relative potencies of carfentanil, etorphine, and thiafentanil in moose are approximately 2:1:1 (McJames et al. 1994, Kreeger et al. 2002). The effects of opioids can be reversed by several opioid antagonists. Naltrexone is the preferred agent due to its potency and l o n g d u r a t i o n ( i . e . , l e s s r i s k o f renarcotization). Other opioid antagonists include naloxone, nalmefene, nalbuphine, and diprenorphine. Cyclohexanes (also known as NMDA antagonists) include ketamine and tiletamine. These drugs are general anesthetics; i.e., they induce unconsciousness and amnesia. However, due to severe side effects like muscle rigidity, frequent convulsions, and rough recoveries, these agents should only be used in combination with an alpha-2 agonist or another tranquilizing or sedative drug (Kreeger et al. 2002). The relative potency between tiletamine and ketamine is approximately 2.5:1 and the duration of action of tiletamine is about three times longer than with ketamine. Tiletamine is not available as a single product and is mar- keted in a 1:1 combination with the benzodiazepine agonist zolazepam. There is no reversal agent to the cyclohexane drugs. Too early administration of an alpha- 2 antagonist in animals immobilized with an alpha-2 agonist in combination with ketamine or tiletamine, may uncover residual side effects of the cyclohexane component and can cause uncontrolled recoveries, hyper- thermia, trauma, and even death (Kreeger et al. 2002). In general, antagonists should be ad- ministered intramuscularly. Intravenous injection of the reversal agent will cause complete recovery in less than one minute in animals immobilized with opioids alone. Such rapid recoveries may be stressful to the animals and may jeopardize the safety of both animals and people. Intravenous administration of reversal agents should therefore only be considered in an emer- gency situation. Carfentanil A large number of free-ranging moose have been immobilized with either carfentanil alone or carfentanil combined with xylazine (Franzmann 1982, 1998; Roffe et al. 2001; Kreeger et al. 2002). Recommended doses of carfentanil alone are 0.01 mg/kg or 3-6 mg/adult. Carfentanil is marketed as a 3 mg/ml solution (Wildnil®, Wildlife Pharma- ceuticals Inc., Ft. Collins, Colorado, USA) and the dose for an adult moose will fit into a standard dart of most remote drug deliv- ery systems. For reversal, naltrexone at 100 mg per mg carfentanil should be admin- istered (Kreeger et al. 2002). In several studies carfentanil at 3-4 mg/ adult has been used in combination with xylazine (e.g., Cervizine® 10 mg/ml, Wild- life Pharmaceuticals Inc.) at 25-175 mg/ adult to improve muscle relaxation and to potentiate the effect of carfentanil so that the opioid part of the combination can be reduced. However, moose immobilized with carfentanil-xylazine are usually not able to support sternal recumbency and may be more susceptible to aspiration pneumonia (Kreeger 2000). Unless there are overrid- ing considerations, the addition of xylazine to opioids in moose is not recommended (Kreeger et al. 2002). If carfentanil is combined with xylazine, the effects of xylazine should be antagonized by either atipamezole (Antisedan® 5 mg/ml, Orion Pharma Animal Health, Turku, Finland) at 1 m g p e r 1 0 m g x y l a z i n e , y o h i m b i n e (Antagonil® 5 mg/ml, Wildlife Pharmaceu- ticals Inc.) at 1 mg per mg xylazine, or tolazoline (Tolazoline® 100 mg/ml, Lloyd Laboratories, Shenandoa, Iowa, USA) at 15 mg per mg xylazine (Roffe et al. 2001, Kreeger et al. 2002, Plumb 2002). IMMOBILIZATION OF MOOSE – ARNEMO ET AL. ALCES VOL. 39, 2003 246 Etorphine Etorphine, alone or in combination with xylazine, has been the drug of choice for moose capture in Scandinavia (Sandegren et al. 1987, Arnemo et al. 2001). Standard doses are 7.5 mg etorphine/adult (Etorphine HCl® 9.8 mg/ml, Vericore Veterinary Prod- ucts, Novartis Animal Health UK Ltd., Litlington, UK) or 2.25 mg etorphine + 10 mg acepromazine/adult (Large Animal Immobilon® 2.25 mg/ml, Vericore Veteri- nary Products, Novartis Animal Health UK Ltd.) combined with 100 mg xylazine/adult (Rompun® Dry Substance, Bayer AG, Leverkusen, Germany). These doses fit into a standard dart of most remote drug delivery systems. Data from 1,464 immobilizations carried out over a 19-year period in Norway (Arnemo et al. 2001; J. M. Arnemo, unpublished data) show that ethorphine alone is an extremely safe and effective drug in moose and there is no indication for combining etorphine with an alpha-2 agonist. Due to the potentiating effect and muscle relaxing properties of alpha-2 agonists, moose immobilized with e t o r p h i n e - x y l a z i n e o r e t o r p h i n e - medetomidine are usually not able to main- tain sternal recumency and regurgitation of rumen contents are frequently seen (J. M. Arnemo, unpublished data). Diprenorphine is a specific antagonist for etorphine and is marketed in the same package as etorphine at a concentration of 1.2 times the concen- tration of etorphine (Diprenorphine HCl® 12 mg/ml and Large Animal Revivon® 3 mg/ml, Vericore Veterinary Products, Novartis Animal Health UK Ltd.). For reversal of etorphine effects in moose, the volume of diprenorphine should be equiva- lent to the total volume of etorphine admin- istered. If etorphine is combined with xylazine or medetomidine, the effects of the alpha-2 agonist should be reversed by atipamezole (Antisedan® 5 mg/ml, Orion Pharma Animal Health, Turku, Finland) at 1 mg per 10 mg xylazine or 5 mg per mg medetomidine (Kreeger et al. 2002). Thiafentanil We are aware of only two reports on the use of thiafentanil for immobilization of free-ranging moose. In one study average down time in moose (n = 18) darted with a standard dose of 10 mg thiafentanil was 1.5 min compared to 4.5 min in moose (n > 100) injected with a standard dose of 4.5 mg carfentanil (Stanley et al. 1989). Reversals of immobilization were achieved with either nalmefene or diprenorphine (no data on a n t a g o n i s t d o s e s w a s p r o v i d e d ) . Renarcotization in animals immobilized with thiafentanil was not observed and the au- thors state that the elimination half-life of thiafentanil is only half as long as the elimi- nation time of carfentanil. Later, McJames et al. (1994) reported that a standard dose of 10 mg thiafentanil was used to immobilize moose from a helicopter in winter. The mean induction time in 59 moose immobi- lized after one injection was 3.6 min. The 10 mg dose was effective for large bulls and safe for calves. Three animals required a second dart to become immobilized and received a total dose of 20 mg thiafentanil. Reversals after different doses of nalmefene (50 and 300 mg) and naltrexone (50 and 100 mg) were rapid and complete with no re- sidual ataxia. Mean standing times ranged from 1.9 to 2.4 min after intramuscular administration of the antagonist in all groups. Renarcotization was not seen and no deaths occurred. Although more studies on its efficacy and safety are required, there are strong indications that thiafentanil may be a very useful drug for immobilization of moose in the future: small volume (1 ml), induction time is rapid, duration of action is short, no major clinical side effects have been re- ported, and renarcotization has not been observed. This view is supported by sev- eral studies on thiafentanil in other ALCES VOL. 39, 2003 ARNEMO ET AL. – IMMOBILIZATION OF MOOSE 247 artiodactylid species (Stanley et al. 1988, Janssen et al. 1993, McJames et al. 1993, Citino et al. 2001, Grobler et al. 2001, Kreeger et al. 2001, Citino et al. 2002). Currently, thiafentanil is only available for investigational purposes (A3080® 10 mg/ ml, Wildlife Pharmaceuticals Inc.). Medetomidine-Ketamine Studies on medetomidine (MED), ketamine (KET), and atipamezole (ATI) in free-ranging moose were performed in Norway and Finland from 1992 to1997. Although some of the data from these stud- ies have been printed in non-indexed sources (Arnemo et al. 1994, Arnemo 1995, Arnemo et al. 1996), they are not easily available to the scientific community. In addition, a lot of useful information is not yet published (J. M. Arnemo and T. Soveri, personal obser- vations). A summary of the results is therefore included here. In summer, 30 mg MED + 400 mg KET (n = 15), 30 mg MED + 500 mg KET (n = 3), and 40 mg MED + 500 mg KET (n = 4) were used to immobilize adults from ground (on foot, stalking, and from a motor vehicle). For reversal, all animals received 5 mg ATI per mg MED, half intravenously or intramuscularly and half subcutaneously. Only a few of the animals were actually seen going down and to avoid stress and excitement during induction, the standard procedure was to wait for 10 min after darting before tracking with a dog was initiated. Mean time (range) from darting until the animal was found was 18 (1-35) min for animals completely immobilized af- ter one dart injection. Mean estimated distance (range) covered after darting was 300 (10-750) m. Two animals darted with 30 MED + 500 KET and one animal darted with 40 mg MED + 500 mg KET required reiteration with a full initial dose to become completely immobilized. One cow in poor body condition darted with 30 mg MED + 400 mg KET developed periodic apnea af- ter 45 min and was treated with ATI (half intravenously and half subcutaneously) to reverse immobilization. One cow injected twice with 40 mg MED + 500 mg KET apparently stopped breathing 40 min after the initial darting and was treated with doxapram (Dopram® 20 mg/ml, Wyeth Lederle, Wyeth-Ayerst International Inc., Philadelphia, Pennsylvania, USA) at 1 mg/ k g i n t r a v e n o u s l y a n d A T I ( h a l f intramuscularly and half subcutaneously). One cow (400 kg) was found drowned in a small creek 13 min after darting with 40 mg MED + 500 KET, 200 m from where she was shot. Necropsy (National Veterinary Institute, Oslo, Norway) revealed no under- lying pathological conditions. No other im- mediate mortalities occurred. Recoveries were uneventful and all animals were stand- ing in less than 11 min after administration of ATI. Animals monitored by radiotracking (n = 17) survived at least 2 months post capture. Data on physiologic parameters (rectal temperature, heart rate, respiratory rate, and relative arterial oxygen saturation) are found in Arnemo et al. (1994) and Arnemo (1995). In winter, 30-40 mg MED + 500 mg KET induced complete immobilization in 6 out of 8 adult cows darted from a motor vehicle at a bait. Four animals were ob- served going down after a mean induction time (range) of 7 (4-11) min while 2 indi- viduals were found after 22 and 43 min, respectively. In two animals the initial dose did not induce recumbency, one of them was manually restrained while the other was captured after an additional dose of 6 mg etorphine. All animals received 5 mg ATI per mg MED for reversal. Recoveries were uneventful and all animals were on their feet in less than 13 min after adminis- tration of ATI. All animals were monitored by radiotracking and survived for at least 9 months post capture. Physiologic data are IMMOBILIZATION OF MOOSE – ARNEMO ET AL. ALCES VOL. 39, 2003 248 found in Arnemo et al. (1994). In winter, 8 adult cows and 5 bulls were darted from a helicopter with 30 mg MED + 400 mg KET (n = 2) or 40 mg MED + 500 mg KET (n = 11). Two animals receiving the highest dose required reiteration with a full initial dose. Mean time (range) from darting to recumbency in animals completely immobilized after one injection was 8 (4-15) min. Two animals injected with the highest dose showed signs of respiratory depres- sion with shallow breathing and periodic apnea. Reversals were achieved with ATI at 5 mg per mg MED injected half intramuscularly and half subcutaneously. One cow that apparently stopped breathing 40 min after darting was treated with doxapram at 1 mg/kg intravenously in addi- tion to ATI, while inspirations were induced by manual chest compressions. This indi- vidual recovered completely. Twelve of the animals were on their feet in less than 10 min after administration of ATI. One bull immobilized with the lowest dose became fully alert after injection of ATI but was apparently unable to get up. The bull was net-lifted with a helicopter to a safe area and was left in sternal recumbency 2.5 hrs post darting. Next morning the bull was tracked for > 1 km with the helicopter but was not observed. All animals were moni- tored by radiotracking and survived for at least 6 months post capture. Based on clinical examination of each individual and the actual body mass of the bull that re- mained recumbent (240 kg), all animals in this part of the study were in very poor body condition. Physiologic data are found in Arnemo et al. (1994). A major part of the MED-KET and ATI evaluation was carried out during 5 winters in Finland from 1993 to 1997. A total of 92 moose were darted from a helicopter: 26 calves (10 females, 16 males), 20 yearlings (17 were of known age) (7 females, 13 males), 26 adult cows, and 20 adult bulls. Standard initial doses were 30 mg MED + 400 mg KET in calves, 40 mg MED + 400 KET in yearlings, and 40 or 50 mg MED + 600 KET in adults. Mean times (range) from darting to recumbency in animals that became completely immobilized after one dart injection were 4.4 (2-7) min in calves (n = 20), 7.6 (5-11) min in yearlings (n = 14), 6.0 (3-10) min (n = 22) in cows, and 5.9 (1-12) min in bulls (n = 14). Animals that required additional dosing to induce com- plete immobilization, animals that were darted more than once due to malfunction- ing darts or bounce offs, and animals that were not observed going down, were not included in the analyses. No animals died during immobilization. However, a total of 4 animals (4.3%) died or were euthanized within 24 hrs post capture. One bull was unable to get up after administration of ATI and was found dead next day. Necropsy (National Veterinary Institute, Oulu, Fin- land) showed very poor body condition, massive lungworm infestation, and signs of circulatory failure. One small calf which was unable to get up after injection of ATI was euthanized next day. Necropsy (Na- tional Veterinary Institute) showed very poor body condition, osteoporosis, and frac- tures in scapula and metatarsus. One small calf and one yearling, both in very poor body condition, recovered after injection of ATI but were found dead next day 100 and 300 m, respectively, from the marking place. Necropsies were not carried out on these two individuals. Three of the deaths (both calves and the yearling) occurred in 1996, a year with extremely harsh winter condi- tions which caused poor body conditions in most of the captured animals. All animals were monitored by radiotracking and no other mortalities occurred within 2 months post capture. The complete set of data from this trial, including serum biochemis- try, is currently being analyzed for publica- tion elsewhere. ALCES VOL. 39, 2003 ARNEMO ET AL. – IMMOBILIZATION OF MOOSE 249 Other Drugs Drug combinations like xylazine- ketamine, xylazine-tiletamine/zolazepam, or medetomidine-tiletamine/zolazepam are not recommended for capture of free-ranging moose (Franzmann 1982, Kreeger et al. 2002; J. M. Arnemo and T. J. Kreeger, unpublished data). Rapid induction is of paramount impor- tance in wildlife capture operations and the enzyme hyaluronidase has been used to increase drug absorption rate (Haigh 1979, Kreeger et al. 2002). However, induction time is more dependent on the injection site and drug dose, and hyaluronidase is prob- ably of benefit only for sub-optimal hits and doses. In addition, there are concerns re- garding the stability of the drug mixture and also the epizootiological aspects of the en- zyme that is a biological product extracted from bovine testes. Moose are often captured during low ambient temperatures in winter and propyl- ene glycol has been added to immobilizing mixtures (xylazine-tiletamine/zolazepam) to avoid freezing (Kreeger et al. 1995). How- ever, in moose darted with 7.5 mg etorphine (1 ml) from a helicopter in winter using standard remote drug delivery equipment (Dan-Inject®, Børkop, Denmark), addition of propylene glycol (0.5 ml) caused delayed inductions (J. M. Arnemo, unpublished data). Ten adult cows were immobilized on 10-11 December 1999, half of them re- ceived etorphine and propylene glycol (group 1) and the other half received etorphine only (group 2). Mean times (range) from initial darting to recumbency were 18 (11-32) min in group 1 and 5 (2-7) min in group 2. Two animals in group 1 required a second dart for immobilization. Mean estimated dis- tances (range) covered after darting were approximately 3 (2-5) km in group 1 and 0.4 (0.1-0.7) km in group 2. The use of propyl- ene glycol as an antifreeze in etorphine mixtures cannot be recommended for moose immobilization. MONITORING AND RISKS Anesthetic Monitoring After capture, immobilized moose should be examined and monitored by a wildlife veterinarian. Clinical problems or injuries should be treated according to established standards in veterinary medicine (Kreeger et al. 2002). Dart wounds are extremely rare in moose if lightweight darts with low impact energy and modern remote drug delivery equipment are used. To avoid bloat and to reduce the risk of regurgitation and aspiration of rumen contents, captured moose should be kept in sternal recumbency with the head higher than the body and the nose lower than the neck. The use of head covers/blinds and ear plugs will reduce stress in animals during handling. For safety reasons, the feet of immobilized animals should be hobbled. Franzmann et al. (1984) established baseline values for rectal temperature (RT), heart rate (HR), and respiratotory rate (RR) in chemically immobilized moose and safe expected ranges were 38.4-38.9 ºC, 70-91 beats/min, and 13-40 respirations/min, re- spectively. Critical values for corrective actions were RT 40.2 ºC, HR 102 beats/ min, and 40 respirations/min. Based on personal experience with moose immobili- zation, we consider these values to be con- servative. Assessment of respiration in immobilized animals can be done by moni- toring of the relative arterial oxygen satura- t i o n ( S p O 2 ) w i t h a p u l s e o x i m e t e r . Hypoxemia is defined as SpO 2 < 90%. In field situations, however, SpO 2 values mark- edly below 90% are often recorded, appar- ently with no harm to the animal. A critical SpO 2 value has not been defined but one of the authors (J. M. Arnemo) usually insti- tutes corrective actions (administration of supplemental oxygen, respiratory stimulants, or specific antagonists) when the SpO 2 falls IMMOBILIZATION OF MOOSE – ARNEMO ET AL. ALCES VOL. 39, 2003 250 below 70%. The trend of SpO 2 values is probably more important than the absolute values and if the SpO 2 steadily decreases, it can be presumed that the animal is in some sort of respiratory crisis (Kreeger et al. 2002). Exertional Myopathy Exertional myopathy (commonly re- ferred to as capture myopathy) is a well- known, usually fatal syndrome in free-rang- ing artiodactylids (Spraker 1993, Williams and Thorne 1996). Exertional myopathy may be caused by several factors, such as stress, chasing, restraint, and transporta- tion. Clinical signs of exertional myopathy may become apparent during the capture p r o c e s s o r m a y o c c u r w i t h i n h o u r s postcapture. It is, however, important to note that the pathologic manifestations of exertional myopathy can be delayed for up to a month following capture before the animal eventually dies (Spraker 1993, Williams and Thorne 1996). Any evaluation of capture methods and drugs in free-rang- ing moose should therefore include a mini- mum of 4 weeks follow-up by radiotelem- etry to detect delayed mortalities caused by exertional myopathy. Risk of Chemical Capture In moose, chemical immobilization is an invaluable tool both for management and research. Since the pioneer days of the 1950s and 1960s, a large number of free- ranging moose have been chemically immo- bilized for various purposes. During the initial phase of moose chemical capture, mortality rates were often very high. In some instances as much as 26% of the animals died, either during the capture proc- ess, during transport, or shortly after re- lease (Franzmann 1982). Main causes of mortality were respiratory depression, car- diovascular collapse, hyperthermia, trauma, stress, and exertional myopathy. Efficient drugs and antagonists have been available for reversible immobilization of moose for at least 2 decades. In addition, remote delivery systems and lightweight darts were developed for non-traumatic administration of drugs. Access to portable and easy to use monitoring devices like pulse oximeters further improved animal safety during field anesthesia. In spite of this progress, reported mortality rates often range from 6 to 19% in moose captured with carfentanil combinations (Roffe et al. 2001). In contrast, only 7 animals (0.5%) died during 1,464 immobilizations carried out with etorphine from helicopter over a 19-year period in Norway (Arnemo et al. 2001; J. M. Arnemo, unpublished data). More than 97% of the animals in this study were moni- tored by radiotracking and no mortalities due to resedation, predation, or exertional myopathy occurred. In a review of stress and exertional myopathy in artiodactylids, Spraker (1993) stated that a mortality rate greater than 2% during trapping is not acceptable. We be- lieve that this rule should be applied also to chemical capture situations: A capture related mortality rate greater than 2% dur- ing chemical immobilization and a 1-month follow-up period is not acceptable for rou- tine captures of moose and requires that the capture protocol be re-evaluated. At least this should be the rule of thumb when a large number (n > 100) of free-ranging moose are being chemically immobilized. Human Safety Although animal welfare is important, the first concern when dealing with wild animals should be the safety of humans (Fowler 1995). Carfentanil, etorphine, and thiafentanil are up to 10,000 times more potent than morphine and minuscule amounts of drug are theoretically lethal to people (Kreeger et al. 2002). Extreme care should therefore be taken when working with po- ALCES VOL. 39, 2003 ARNEMO ET AL. – IMMOBILIZATION OF MOOSE 251 tent opioids and lost darts should be of major concern. Other drugs and drug combina- tions at doses prepared for moose are also potentially dangerous and all personnel in- volved in moose captures should therefore be qualified to perform first aid on humans. A brief update on human medical treatment following accidental exposure to immobilis- ing drugs is found in Kreeger et al. (2002). Most drugs used for moose capture are colourless. As a safety precaution, drugs may be coloured to make it easier to detect leakage from vials, needles, darts, and in- jection sites. Congo red and cobalt blue are commonly used for this purpose (Nielsen 1999). The use of dart guns requires an understanding of ballistics and gun safety and readers are referred to recent publica- tions on wildlife chemical immobilization (Nielsen 1999, Kreeger et al. 2002). Overviews of safety aspects regarding heli- copter operations were provided by Nielsen (1999). RECOMMENDATIONS For routine immobilization of free-rang- ing moose, we recommend carfentanil at 0.01 mg/kg or etorphine at 7.5 mg total dose per adult. At these doses most animals are able to maintain sternal recumbency. We do not advocate combining opioids with xylazine or other sedative drugs because this will often induce lateral recumbency and thereby increase the risk for tympany, regurgitation, and aspiration of rumen con- tents. 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