Abstract

Twelve plains bison (Bison bison bison) (PB) and eleven bighorn sheep (Ovis canadensis canadensis) (BHS) were successfully immobilized using a partially reversible combination of tiletamine-zolazepam-xylazine-hydromorphone. PB were darted from a helicopter in March 2005 and 2006 in Prince Albert National Park, Canada and BHS were darted from the ground in February 2006 in Kootenay National Park, Canada. Darting was accomplished with either a Dan-inject® (Dan-Inject of North America, Fort Collins, CO) model JM rifle with pressurized darts or a Pneu-dart® (Pneu-Dart Inc., Williamsport, PA) model 196 rifle with powder-charged darts. BHS were either weighed directly (n=7) or body weight was estimated from a chest girth measurement (N=4) while body weights for PB were estimated from PB of known age, sex, and weight occupying similar habitat from Elk Island National Park, Canada. Both xylazine HCl (Bayer Inc., Toronto, ON, Canada) and hydromorphone (Sabex Inc., Boucherville, QC, Canada) were used to reconstitute vials of tiletamine-zolazepam (Telazol®, Fort Dodge Animal Health, Fort Dodge, IA) at a fixed ratio of 1.5 to 1 to 0.2 of tiletamine-zolazepam, xylazine, and hydromorphone, respectively. The drug solution was prepared as follows: 1.32 ml of xylazine HCl (250 mg/ml lyophilized from 100 mg/ml solution and reconstituted) and 0.67 ml of hydromorphone (100 mg/ml) were used to reconstitute a 500 mg vial of tiletamine-zolazepam. The mixed solution had a final volume of 2.6 ml that contained approximately 192 mg/ml of tiletamine-zolazepam, 128 mg/ml of xylazine, and 25 mg/ml of hydromorphone.

Immobilized animals were blindfolded and placed in sternal recumbency. Venous blood was drawn from the jugular vein and arterial blood was drawn from coccygeal or femoral artery in bison. Oxygen saturation and pulse were determined with a pulse oximeter probe placed on either the tongue or inserted in the rectum (Model V3402, Surgivet Inc., Waukesha, WI). Blood gas values were analyzed within three hours with a handheld analyzer (i-STAT Portable Clinical Analyzer, i-STAT Corporation, East Windsor, NJ). Hydromorphone was reversed in both PB and BHS with naltrexone (Wildlife Pharmaceuticals Canada, Calgary, AB) at a dosage of 0.05 to 0.1 mg/kg intramuscularly. In PB, xylazine was reversed with tolazoline HCl (Summit Veterinary Pharmacy, Aurora, ON) at a dosage of 3 to 4 mg/kg injected half IV and half IM in BHS. Xylazine was reversed with either tolazoline as described for PB or atipamezole (Novartis Animal Health Canada Inc., Mississauga, ON) injected IM at 0.1 mg/kg. The zolazepam component of tiletamine-zolazepam was not reversed due to the low dosage used, even though specific benzodiazepine antagonists are available. Statistical significance was assessed using a single factor ANOVA with alpha=0.05 and p≤0.05 considered significantly different for induction time, reversal time, and handling duration.

Dosages and immobilization characteristics were very similar regardless of species (Tables 1 and 2). Higher initial dosages of tiletamine-zolazepam, xylazine, and hydromorphone were used for PB immobilized with a single dart (Table 1) due to capture and pursuit method (helicopter). Multiple darts were required to achieve immobilization in both PB and BHS due to failure of complete ejection of dart contents (n=5), poor dart site (n=2), or weight underestimate (n=1). Induction and reversals were smooth and rapid, and times were comparable to published dosages of medetomidine-tiletamine-zolazepam and carfentanil-xylazine combinations for PB^1,2 and faster than previous studies using tiletamine-zolazepam-xylazine or ketamine-xylazine combinations for BHS.^3,4 Two additional PB did not become immobilized after being darted and chase was abandoned when no drug effects were observed after 10 minutes, while all 11 BHS that were darted were successfully immobilized.

Table 1. Mean (± SD) dosages (mg/kg) of drugs used for immobilization and reversal of plains bison and bighorn sheep

^aTwo or more darts required for induction.

Table 2. Comparative immobilization characteristics for plains bison and bighorn sheep
immobilized with tiletamine-zolazepam-xylazine-hydromorphone (Mean ± SD)

^aTime from dart injection to sternal recumbency.
^bTime from sternal recumbency to standing following reversal.
^cTime from injection of reversal drug until ambulatory.
^dCumulative chase time not including time required to slowly haze bison into open areas.
^eSkewed mean due to single BHS with 48-min induction time due to multiple darts.

In contrast to tiletamine-zolazepam-xylazine combinations without hydromorphone,^1,3 both PB and BHS reversed quickly and smoothly using either tolazoline or atipamezole to reverse xylazine and naltrexone to reverse hydromorphone. No significant difference in reversal time was observed between BHS reversed with tolazoline or atipamezole. Mean induction and reversal times were significantly longer for both PB and BHS immobilized with multiple darts versus single darts, although handling duration did not differ (Table 2). Mean (±SD) oxygen saturation measured with a pulse oximeter was 83.6±7.6% in BHS (range 66–98%) and 82.5±7.9% in PB (range 66–96%). Mild to moderate hypoxemia was observed in both BHS and PB, but values were superior to those reported for bison immobilized with tiletamine-zolazepam-xylazine alone,¹ and supplemental oxygen was not considered necessary in any animal. All animals were tractable, relaxed, and in a satisfactory plane of anesthesia to allow minor procedures such as radio-collaring, rectal palpation, and venipuncture without spontaneous arousal. Profuse salivation was noted in approximately one-third of BHS immobilized with this combination. Blood gas data collected on seven PB (Table 3) indicated mild to moderate hypoxemia with some evidence of hypoventilation based on PaCO₂ values. All PB demonstrated moderate to severe metabolic acidosis and increased serum lactate. This probably resulted from the helicopter pursuit prior to capture. Hypoxemia is a frequent complication when using tiletamine-zolazepam-xylazine or narcotic-alpha-2 agonist combinations in large ungulates.^5,6,7 No mortality or renarcotization was observed in any animal immobilized in this study. Mean drug volumes to achieve immobilization using single darts were 4.24±0.42 ml for PB and 0.78±0.13 ml for BHS, allowing the use of smaller drug volumes compared to tiletamine-zolazepam-xylazine combinations.^1,3 These drug volumes are comparable to other potent drug combinations for PB and BHS.^8,9,10 Reversal times were faster and more complete than reported with tiletamine-zolazepam-xylazine combinations from other studies with BHS³ and PB¹ due to lower dosages of tiletamine-zolazepam and xylazine that could be used as a result of combining these drugs with hydromorphone. This combination seems to be an effective alternative to provide safe, reliable, reversible immobilization of free-ranging BHS and PB with few complications and relatively low cost. Advantages include low volume, rapid and complete reversal, and relative lack of side effects.

Table 3. Blood gas values for plains bison immobilized
with tiletamine-zolazepam-xylazine-hydromorphone (n=7)

Acknowledgments

The assistance of Parks Canada staff in Kootenay and Prince Albert National Parks is gratefully acknowledged, particularly Alan Dibb, Sybilla Helms, Nicole Obee, Ronan Eustace, Dan Frandsen, and Lloyd O’Brodovich. Helicopter capture was possible with the services provided by Bob Doerksen of Transwest Air.

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