Survival and immobilizing moose with carfentanil and xylazine

Animal

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Survival

Care

and

Handling

MOOSE IMMOBILIZATION

and

moose immobilizing carfentanil and xylazine

with

ThomasJ. Roffe, KennethCoffin,and Joel Berger Abstract The use of carfentanilwith other drugsto immobilize moose (Alces alces) has yielded

mixed results. Previousworkon chemicallyimmobilizingmoose with these drugsreported mortalityof 6-19%. Eventhe most recentstudyof free-rangingmoose usingthe same drug combinationas we used in this report(carfentaniland xylazine) had 6% mortality within several days of immobilization. Anotherrecent study suggestedthat carfentanilxylazine produced unsatisfactoryresults in moose throughexacerbatedmortalityrisks induced by xylazine. As partof an ongoing studyof carnivoreeffectson moose populations, we chemically immobilized48 moose (41 adult females, one immaturemale, 6 calves) by charge-powereddart. Low-stresstechniques were used, including quiet groundstalksby one individualand use of blindfoldsand low noise duringprocessing.

On our few aerial captureswe immediatelywithdrewthe helicopteronce the dartwas placed and landed during induction. We found that capture-relatedmortalitycan be minimizedby using effective immobilizationdosages that maintainsternalrecumbency, and subcutaneousroutes,by effectivelyantagby providingnaltrexoneby intramuscular and low-stress onizing xylazine, by using techniques. Femalemoose survivalwas diminished when body conditionwas below a threshold,and some mortalityoccurred,likely due to poor condition per se and not as a direct resultof immobilization.We providea field protocoland drugdoses thatwildlife managerscan use to safely immobilizemoose.

GreaterYellowstone Area,moose, naltrexone,xylazine Key words carfentanil,chemicalimmobilization, Carfentanil has been used successfully to immobilize moose (Alces alces) since the early 1980s (Franzmann et al. 1984, Meuleman et al. 1984, Seal et al. 1985, Schmitt and Dalton 1987, Delvaux et al.

1999) with more consistency than other drugs, such as ketamine-xylazine orTelazol? (Franzmann 1982, Garner and Addison 1994). However, mortality rates typically ranged from 6 to 19%, and when carfentanil was combined with xylazine in a captive setting, mortality exceeded 80% (Kreeger 2000). Other potent narcotics, e.g., etorphine (Gasaway et al.

1978, Lynch 1981), can produce mortality rates typical of carfentanil. Different studies arrive at discordant conclusions about the effectiveness of drugs

based on success of operations. We suggest that methodology, including field capture protocol and drug types and doses, is related causally to variation in immobilization performance and animal survival.

As part of a broader study of the effects on moose of recolonizing wolves (Canis lupus) and grizzly bears (Ursus arctos) (Berger et al. 1999, Berger et al.

2001), we captured moose to fit radiocollars for long-term monitoring of reproduction in known individuals. We also caught moose as part of management responses in Montana. Here we report extremely low capture-related mortality in these moose from southern Montana and northwest Wyoming. Understanding sources of capture-

AddressforThomasJ. Roffeand KennethCoffin:BiologicalResourcesDivision,UnitedStatesGeologicalSurvey,FWPBuilding, MontanaStateUniversity,1400 S 19th St., Bozeman,MT 59718-5496, USA;e-mailfor Roffe:troffe@montana.edu.

Addressfor Joel Berger:WildlifeConservationSociety,Box 340, Moose,WY83012.

WildlifeSociety Bulletin2001, 29(4):1140-1146

Peerrefereed

Moose immobilization * Roffe et al.

Following immobilization, a cow moose fitted with a radiocollar departs the capture scene in Grand Teton National Park.

related mortality is important to managers in selecting a capture protocol. Whereas our drug doses were similar to those in past studies (see Delvaux et al. 1999), we believe our low mortality was a consequence of our low-stress ground darting techniques.

However, we also experienced greater success than others using ground darting, and this is likely related to drug dose and delivery (Kreeger 2000).

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longer than 5 minutes. For analyses of doses and immobilization times, we used data from 40 of the 48 moose (36 adults, 4 calves) because they were all captured with a single dart, once/year, and we have accurate induction times. Induction time was measured from dart strike to recumbency. Down time was from recumbency to standing. Recovery time was from injection of antagonists until standing and ambulatory. Antagonists were delivered individually by hand injection using a 12-ml syringe and 18-gauge, 3.8-cm needle.

Immobilized moose were approached quietly and a blindfold was placed across the eyes. Talking and other noises were kept to a minimum, and personnel were moved >18 m from the moose during the recovery phase. We monitored for rumen reflux by observation and occasionally for aspiration by auscultation.

Physical condition is frequently assessed in domestic ruminants by palpation, particularly over bony prominences with greater soft-tissue thickness

Methods We immobilized 41 female, one subadult male (included with adults), and 6 calf moose during winter (Jan-Feb) in Grand Teton 1996-2000 National Park and Grey's River,Wyoming (42053' to 43?52'N, 110032' to 110051'W), and southwest Montana. The 45 moose in Wyoming received radiocollars (Advanced Telemetry Systems, Isanti, Minn., USA), providing the opportunity for longterm followup.

We approached 42 moose by snowshoeing to within 20-60 m. Only 1-2 people approached before the animal was immobilized. We darted 6 adult moose from a helicopter in January 1999. Following successful dart delivery, the helicopter was pulled away and grounded during induction. Helicopter darting was used on the few moose too difficult to approach from the ground.

We remotely delivered immobilizing drugs (carfentanil 3 mg/mL [Wildnil?], and xylazine 100 mg/mL [Cervizine?] ,Wildlife Pharmaceuticals, Fort Collins, Colo., USA) by 2-cc disposable darts (3.8-cm barbed needle) from a 0.50-caliber scoped Pneudart Model 193 rifle (Pneudart, Williamsport, Pa., USA). Helicopter darting was done with an opensite Model 193 rifle, and we did not chase moose

Dr. T. J. Roffe collects blood from immobilized moose while assistant Gabriel Roffe positions head and neck.

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Wildlife Society Bulletin 2001, 29(4):1140-1146

indicative of better (greater fat) condition (Terra 1990). Body-condition indices frequently include rib prominence as an assessment criterion (Maas 1990). Based on these routine veterinary procedures and our previous experience with assessing body condition at postmortem, we decided to try simple measurement of moose rib fat to index body condition. We determined rib fat by separating the hair and making a small stab incision with a clean scalpel over the mid-shaft last rib to the perios-

was 127(+9.6):1. We administered naltrexone predominantly by intramuscular and subcutaneous injection (divided roughly 1/3 and 2/3, respectively), although in 1996 we reversed some animals by including an intravenous route of administration (providing 50 mg by this route). We administered yohimbine and tolazoline intravenously. There was no difference (t11=0.9, P=0.38) in recovery times between moose given naltrexone intravenously (recovery time x=5.2 +1.0 minutes) and moose given naltrexone excluding an intravenous dose (recovery time = 5.9+ 1.8 minutes) with the same alpha-adrenergic antagonist. We observed no differences in clinical signs (steadiness, rapidity to standing, gait) between the 2 groups. Mean doses of tolazoline, yohimbine, and naltrexone were 828.6 (?114.6) mg, 46.2 (?8.7) mg, and 447.2 (?31.5) mg, respectively. Mean recovery time was briefer, although not significantly, for animals reversed with tolazoline (4.7 1.5 minutes) than with yohimbine (5.9? 1.9minutes) (t22= 1.9, P= 0.07). Ataxia and decreased alertness (ears and eyes lacking focus on objects and noise) was common in yohimbine-recovered moose and absent in tolazoline-recovered moose.

Four calves received a mean carfentanil dose of 3.15 (?0.52) mg (range=2.7-3.6 mg, estimated

teum. A 1-mm-diametermetal probe, attached and

dosage = 0.005 mg/kg-0.04

calibrated to a micrometer, was inserted into the incision and depth was measured. The site was not otherwise manipulated.

xylazine dose of 50 (?11.5) mg (range=40-60 mg, estimated dosage=0.17 mg/kg-0.3 mg/kg). Mean naltrexone dose was 400 (+57.7) mg, mean naltrexone to carfentanil ratio was 127(?2.7):1, and mean tolazoline dose was 575 (?206.2) mg. Mean induction, down, and recovery times were 2.7 (?1.9) minutes, 21.1 (?9.1) minutes, and 5.2 (?0.8) minutes, respectively. We opportunistically darted one small orphaned calf (estimated body mass 90 kg) with an adult dose (3.6mg carfentanil + 60mg xylazine) when searching for an adult animal. After an induction time of 40 seconds, the calf was very limp, but otherwise handled the anesthesia well. We did not measure rib fat on this animal due to depth of anesthesia and our desire to rapidly reverse the anesthesia. She was given intramuscular and subcutaneous naltrexone and intravenous tolazoline, and was monitored for 3 months before recovered, her death due to starvation on 18 May 1998.

Only 2 immobilized adult moose and one calf slumped into partial (adults) or complete (calf) lateral recumbency. We did not observe rumen reflux or auscult fluid sounds over the trachea in any immobilized moose. A few moose coughed forcibly

Immobilized moose shortly after injection of reversing agents, naltrexone and tolazoline. Note the position of the head and body while the animal is under the effects of immobilizing drugs.

Results We used 3.3-3.6 mg (estimated dosage=0.008 mg/kg) carfentanil combined with mg/kg-0.013 50-60 mg (estimated dosage=0.12 mg/kg-0.22 Two moose mg/kg) xylazine in adult moose. required supplemental doses of 0.6 and 0.3 mg carfentanil once sternal. Mean (?SD) carfentanil and xylazine doses for adult moose were 3.52 (?0.12) mg and 58.8 (?3.2) mg, respectively. Mean induction time was 4.4 (?1.9) minutes (range= 1.8-8.8 minutes), and mean down time was 26.0 (?6.1) minutes (range= 12.4-37.4 minutes).

We antagonized our immobilizing drugs with 400-500 mg naltrexone (50 mg/ml; Trexonil?, Wildlife Pharmaceuticals) and 30-60 mg yohimbine (1996-1997; 5 mg/ml; Antagonil?, Wildlife Pharmaceuticals) or 400-900 mg tolazoline (1998-2000; 100 mg/ml; Tolazine?, Lloyd Laboratories, Shenandoah, Ia., USA). Mean naltrexone to carfentanil ratio

mg/kg) and mean

Moose immobilization 2-3 times once recovered and standing. All moose resumed browsing and eating snow after recovery.

One moose died within 10 days of immobilization. This adult was lethargic upon approach and grossly thin to palpation. Her rib fat thickness was 0.30 cm during immobilization, the lowest measured in adult moose, and bone marrow was red and gelatinous at necropsy. An adult moose died of starvation at 2 weeks post-immobilization and the orphaned calf at 5 weeks post-immobilization. At postmortem, bone marrow was red and gelatinous in these 2 moose. Together,these 3 animals had the least rib fat measurements of all moose in the study, and postmortem findings supported starvation as cause of death. Three other starvation-relatedmortalities occurred in adult females >1 year after immobilization. The rib fat thicknesses of these 3 adults (0.38, 0.37, and 0.30 cm taken at postmortem) were less than or equal to fat levels of any adult females that survived. Rib fat measurements of adult moose ranged from 0.30 to 0.79 cm. Mean rib fat of all moose, including calves, was 0.48 cm (?0.13, range=0.28 to 0.79). Female moose that survived winter had greater mean rib fat measures (0.50+0.02 cm) than those that did not (0.35+0.02 cm) (t32= 4.97, P<0.001 for one-tail hypothesis).

Roffe et al.

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result in error at estimating capture-related mortality and consequently failure to accurately assess effectiveness of a capture protocol. Our data from animals we monitored over the 5 years of the study suggest that recently captured moose were no more or less susceptible to starvation-emaciation, and it is unlikely that immobilization played a role in causing starvation.

If we exclude starvation-related mortality, we essentially had no capture-related mortality in moose. Many studies do not defie a post-immobilization time period for capture-related mortality (e.g., Franzmann 1982, Garner and Addison 1994), generally considering only mortality during and immediately following the capture as capture-related. Others use short times such as 12 hours (e.g., Ferreraset al. 1994),"days"(Seal et al. 1985), or up to a week (Schmitt and Dalton 1987). Applyingeven an arbitrarystandardfor capture-relatedmortality,such as any mortality within 10 days, our maximum capture-relatedmortalitywould have been 1/48 (2%).

Renarcotization occurs when opioid antagonist activity decreases to ineffective levels before the agonist is eliminated from the body. This effect can occur by using long half-life agonists, short half-life antagonists, or reabsorption (e.g., enterohepatic recirculation) of the agonist. Antagonists like diprenorphine,which also have some agonistic activDiscussion ity, lead to renarcotization and mortality (Seal et al.

Our data demonstrate that moose can be safely 1985, Schmitt and Aho 1988). Naltrexone is a pure immobilized chemically with carfentanil and narcotic antagonist with a binding affinity for morxylazine with very low mortality rates, provided phine receptor sites thousands of times that of carstress is minimized and potential renarcotization fentanil. The current labeling for naltrexone use sugand aspiration pneumonia are prevented. We pre- gests use of a 100:1 ratio (naltrexone to carfentanil) vented aspiration pneumonia by using drug doses in large wild ungulates, delivered by immediate that allowed the moose to maintain a sternal pos- sequential intravenous and subcutaneous routes. ture and an elevated head. We believe the one mor- Haigh and Gates (1995) recommended a minimum tality within 10 days of immobilization was related ratio of 125:1 to prevent renarcotization in bison to malnutrition and starvation rather than chemical (Bison bison). We used similarly high antagoimmobilization. Our data on rib fat, postmortem nist:agonist ratios in moose and did not experience fat, and postmortem cause-of-death suggest that rib anesthetic-related mortality. However, route of fat is a good index of body condition. Measurement administrationalso may play a role. Delvaux et al. of rib fat during immobilization in this moose pro- (1999) used a 100:1 ratio but delivered naltrexone vided an objective criterion to support our subjec- by intravenousand intramuscularroutes. They expetive assessment of her extremely poor body condi- rienced a 6%mortality rate in moose in Canada.We tion during immobilization. Postmortem supported believe subcutaneous delivery of naltrexone is a diagnosis of emaciation. Of particular note was important but could find no survival or recovery the mortality of an adult female whose postmortem advantagefor intravenous delivery of naltrexone (as rib fat measurement was 0.30 cm. This moose was labeled) versus intramuscularuse. scheduled for a collar replacement but died the day Stress also plays an important role in recovery before we were to immobilize her. Failure to take and subsequent mortality. Effects of stress, hyperthese objective measures of body condition can thermia, and capture myopathy in ungulates have

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Wildlife Society Bulletin 2001, 29(4): 1140-1146

been well documented in the literature (e.g., see study. Our results do not support xylazine as a risk Franzmann 1982). In moose, reports have shown factor for aspiration pneumonia in moose. The clinincreased mortality in animals moved to relocation ical description of anesthesia (Kreeger 2000) sugsites compared to handled and released moose gests that other factors-such as immobilant dose and depth of anesthesia, hay feed, moose density (Schmitt and Dalton 1987). Others have shown that stress associated with helicopter capture and social factors associated with captivity, differincreases mortality, presumably due to the considences in alpha-2 antagonists used, or interactions erably greater running time and elevated body tem- among these variables-are more likely explanaperatures caused by chasing (Lynch 1981, Olter- tions. In our study, most of our moose remained mann et al. 1994). Schwartz et al. (1997) did not sternal,often with head elevated. Moose body mass in moose immobilized mortality was estimated in the Kreeger (2000) and our studexperience they from the ground in a confined environment. These ies; however, our slower induction times support moose were likely habituated and were certainly the possibility that we used a lower dosage. unable to flee to evade capture and thereby increase body temperature. Even though their aniConclusions mals were not wild and free-ranging, their results the of mimic effect low-stress capture methods Our moose capture protocol evolved during the may in free-ranging moose.

5 years of our study. Dosing regimens changed to a Our one-time use of helicopter capture was greater carfentanil:xylazine ratio as we found that restricted to moose that were inaccessible from the moose tolerated the narcotic better than alphaground and needed immediate collar replacement. adrenergics like xylazine. We recommend 3.3-3.6 Our pursuit times were kept to <5 minutes and the mg carfentanil with 50-60 mg xylazine in adult helicopter was grounded during induction. All of female moose regardless of body mass. Our one our captures also were made during winter, usually subadult male of similar body size also was sucin deep snow. Our aerial protocol and environcessfully immobilized with this dose. This dose genmental conditions, therefore, limited pursuit time erally renders the animal immobile, very tractable and provided better ambient cooling. We successfor handling, but sternal with elevated head. We find that an advantage to the combination drug profully immobilized 6 moose from helicopter. While the number is small, all 6 moose remained within tocol is that it provides better relaxation of moose visual range during induction and none moved at a for reproductive examination and blood sampling.

Relaxation also likely reduces the tendency of pace faster than a walk after darting and pulling Our of the moose to fall into lateral recumbency through leg away. technique grounding helicopter on nearby, slightly higher ground during induction movements and rigidity. We also suggest that to get may have lessened the flight response of moose. equivalent depths of anesthesia, less narcotic needs We believe our low-stress techniques, minimizing to be used when combined with xylazine. We recthe buildup of body heat through chases, and quiet ommend covering the eyes and maintaining quiet to minimize external stimuli while handling moose. handling and use of blindfolds played an important role in our success compared to previous reports Our standard antagonist protocol for adult moose consists of 800 mg tolazoline delivered intrausing helicopter darting. While it is likely we could have sustained low mortality using this technique venously, followed immediately by 450 mg naltrexon a larger number of animals, based on moose one, with 30-50% given intramuscular and the remainder subcutaneously. It is likely that lower flight response to initial approaches, helicopter capture is still considerably more stressful than doses of tolazoline, such as 600 mg, would be as ground-based approach. Had we used this techeffective, though moose tolerate this drug quite well. Moose appear more resistant to adverse carnique throughout our study, we may have increased our overall mortality rate for captured moose. diovascular and gastrointestinal side effects of tolathat carfentanilzoline than some other ungulates such as bison (T. Kreeger (2000) reported xylazine was likely responsible for aspiration pneu- J. Roffe, unpublished data). We have found no monia in 9 of 11 moose immobilized with this comadvantage to providing an intravenous dose of nalbination. Although he suggested that xylazine was trexone, but recommend that the narcotic and for the he acknowlresponsible high mortality, alpha-adrenergic be antagonized. Although the other and limitations of his adult edged possibilities immobilizing dose was safe in the few calves

Moose immobilization * Roffe et al. we did at this dosage, the level of anesthesia is deeper than necessary to carry out most handling and minor surgical procedures. Our standard dose for very young calves to yearlings is 2.7 mg carfentanil with 40 mg xylazine.

This anesthesia is reversed by 350 mg naltrexone and 400 mg tolazoline delivered as above.

We thank the staff of Grand Acknowledgments.

Teton National Park for their frequent assistance in visitor and vehicle control, S. Cain and G. Roffe for help in conducting some of the immobilizations, M. Reid for additional ground support, and S. Sweeney for editorial review of this manuscript. Funding was provided by the United States Geological Survey, National Science Foundation, the Wildlife Conservation Society, and University of Nevada, Reno.

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Thomas Roffe (above) is a wildlife veterinarian, ecologist, and program manager with the United States Geological Survey, Biological Resources Division, in Bozeman, Montana. As the Department of Interior's chief expert on brucellosis in the Greater Yellowstone Area, he supervises research and provides technical support to the National ParkService and United States Fish and Wildlife Service on wildlife health issues. Tom holds a B.A. in biology from the University of California, Santa Cruz, a Ph.D. in marine ecology from Oregon State University, a DVM from Oregon and Washington State universities, and a veterinary pathology residency from the University of Tennessee.

Before moving to Bozeman, Tom worked as a wildlife disease

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WildlitfeSociety Bulletin 2001, 29(4): 1140-1146

specialist and section chief at the National Wildlife Health Center in Madison, Wisconsin. Outside of work, he enjoys horseback riding, hunting, and hiking with his dogs. Kenneth W. Coffin (right) received both his B.S. in biology and M.S. in wildlife management from Montana State University. Since 1994, Ken has worked on a variety of wildlife management issues including wildlife diseases, endangered species recovery, and forest carnivore research. Ken is currently a writer-editor with the United States Forest Service on the Tongass National Forest. Joel Berger (left) is a senior field biologist (North America Programs) for the Wildlife Conservation Society, having

obtained his B.A. and M.S. from California State University, Northridge, and his Ph.D. at the University of Colorado, and having done a postdoctoral at the Smithsonian Institution'sConservation and Research Center.

Associate editor. Krausman