Abstract

The study was designed to determine the efficacy and physiologic effects of two potentially useful combinations for the immobilization of bison. Medetomidine-Telazol^® (MZT) is a potent, low volume solution that may be a good choice for immobilization of free-ranging bison. Xylazine-Telazol^® (XZT) is a higher volume solution that may be more effectively used on captive or game-farmed bison. Seven male wood bison (Bison bison athabascae) received 1.5 mg/kg of xylazine + 3 mg/kg of Telazol^®, and on another occasion 60 µg/kg of medetomidine + 1.2 mg/kg of Telazol^®. Both combinations produced effective immobilization. Induction was significantly faster with XZT; recovery was significantly faster with MZT. Quality of immobilization was good with both treatments. Blood pressure was significantly higher with MZT. The major complication was hypoxemia which occurred with both combinations.

Introduction

Bison are becoming increasingly popular as a game-farmed species. Bison must be immobilized for a variety of reasons and can be a difficult animal to work with. Historically, muscle relaxant drugs, such as succinylcholine were used to produce immobilization. Humane aspects and low therapeutic index limit the acceptability of this drug. High doses of xylazine have been advocated, this often fails to immobilize the animal and can result in bloat, regurgitation, and other complications. Telazol^® has been used, but it can result in rough inductions and recoveries. Medetomidine-ketamine immobilization has not been reported in North American bison but has been reported in Wisent (Bison bonasus).⁶ Potent narcotics, such as carfentanil, will produce effective immobilization of free-ranging bison.^4,7 Many wildlife managers and veterinarians are unwilling to use this drug due to safety concerns.

The following paper detail results of a study designed to determine the efficacy and physiologic effects of two potentially useful combinations. Medetomidine-Telazol^® (MZT) is a potent, low volume solution that may be a good choice for immobilization of free-ranging bison. Xylazine-Telazol^® (XZT) is a higher volume solution that may be more effectively used on captive or game-farmed bison, where small, accurate darting systems are less critical.

Materials and Methods

This study was performed during February of 1998, in Elk Island National Park, AB, Canada. Seven male wood bison were used in the study (five 3-year-olds, one 4-year-old, and one 5-year-old). The average weight of the bison was 413±35 kg (386–462 kg). Bison were fasted for at least 24 hours prior to drug injection. Each bison received both combinations in random order. The treatments were administered 1 week apart to allow for drug metabolism and excretion. The drug solutions were prepared as follows. For XZT 2.5 ml of xylazine was added to a vial of Telazol^®, the resulting solution had a volume of 2.8 ml and contained approximately 89 mg/ml of xylazine and 178 mg/ml of Telazol^®. For MZT 2.5 ml of 10 mg/ml medetomidine solution was added to a vial of Telazol^®, the resulting solution contained approximately 8.9 mg/ml of medetomidine and 178 mg/ml of Telazol^®.

On the day of the study the bison was moved through a handling facility into a hydraulic chute. The bison was weighed and received either 1.5 mg/kg of xylazine + 3 mg/kg of Telazol^®, or 60 µg/kg of medetomidine + 1.2 mg/kg of Telazol^®. The drugs were administered by hand injection into the gluteal muscle mass. Following injection, the bison were released from the chute and moved into a holding pen. The time from injection to sternal recumbency and head down was recorded. Once it was safe to move into the pen the bison was restrained in lateral recumbency. A 20-g, 5-cm catheter was placed in the saphenous artery for pressure measurement and arterial blood sampling. The catheter was connected, with non-compliant tubing, to a Baxter^® pressure transducer. The transducer was connected to a Propaq 104 EL^® physiologic monitor. ECG leads were placed in a three-lead axis, and a lead II ECG was constantly monitored. Body temperature was measured rectally with a digital thermometer. Heart rate (HR), respiratory rate (RR), body temperature (temp), and mean arterial pressure (MAP) were recorded every 5 minutes. PaCO₂, PaO₂, pH, and base excess (BE) were measured with a blood gas analyzer at 15-, 30-, 45-, and 60-minutes post injection. Blood gas samples were stored on ice and analyzed within 3 hours from collection. Samples were corrected for hemoglobin concentration and body temperature.

Physical qualities of immobilization, incidence of ruminal tympany, and regurgitation were also noted. At 60-minutes post injection equipment was removed from the animal and alpha-2 antagonist agents were administered. Atipamezole was administered, at a dose of 90 µg/kg IV and 90 µg/kg IM, to antagonize medetomidine. Tolazine was administered, at a dose of 1.5 mg/kg IV and 1.5 mg/kg IM, to antagonize xylazine. The time from antagonist administration to sternal recumbency and standing was recorded.

Results

A comparison of HR, RR, MAP, and temp can be found in Figure 1. A comparison of pH, PaO₂, PaCO₂, and BE can be found in Figure 2. Hyperpnea was present with both combinations, RR was significantly lower with XZT. RR did not change significantly over time. HR was not significantly different between treatments and did not change significantly over time. MAP was significantly lower with XZT and did not change over time with either treatment. Temp was not significantly different between treatments and did not change over time. Arterial pH was not significantly different between treatments. Arterial pH increased significantly over time with both treatments. Both treatments produced some hypoventilation, evidenced by increased PaCO₂. PaCO₂ was significantly higher with XZT. PaCO₂ increased significantly over time during immobilization with MZT. Both combinations produced hypoxemia (PaO₂<60 mm Hg) throughout the immobilization. PaO₂ decreased over time with both treatments. The lowest mean PaO₂ produced by MZT was 46.9±7.6 mm Hg at 45-minutes post injection. The lowest mean PaO₂ produced by XZT was 44.4±5.3 mm Hg at 30-minutes post injection. BE was not significantly different between treatments, and increased significantly over time with both treatments.

Figure 1

Comparison of physiologic responses of seven subadult wood bison during anesthesia with MZT, and during anesthesia with XZT. Means and standard deviation bars are presented for wood bison anesthetized with MZT (“), and with XZT (!). Significant differences (p<0.05) between drug treatments at specific time points are indicated by an asterisk (*).

Figure 2

Comparison of blood gas responses of seven subadult wood bison during anesthesia with MZT and during anesthesia with XZT. Means and standard deviation bars are presented for wood bison anesthetized with MZT (“) and with XZT with (!). Significant differences (p<0.05) between drug treatments at specific time points are indicated by an asterisk (*).

Immobilization data can be found in Table 1. Induction was significantly faster with XZT, recovery was significantly faster with MZT. Quality of immobilization was good with both treatments. XZT appeared to be slightly shorter acting, with some animals demonstrating ear and limb movement at 55-minutes post injection. Mild ruminal tympany was present with both treatments. One animal regurgitated 16-minutes post reversal with tolazoline. The average drug volume used was 7 ml with XZT and 2.78 ml with MZT.

Table 1. Comparative immobilization features of medetomidine-Telazol^® (MZT) anesthesia with atipamezole reversal, and xylazine-Telazol^® (XZT) anesthesia with tolazoline reversal, in wood bison.

Paired t-test used to compare immobilization data of seven wood bison. Statistical significance at p<0.05 indicated by asterisk.

Discussion

Both of these combinations should prove to be useful for immobilization of bison. The major complication of immobilization was hypoxemia. Hypoxemia is common in ruminants anesthetized with medetomidine based protocols.^1-3,5 Hypoxemia has also been noted during xylazine sedation or anesthesia in ruminants.⁸ Two other factors probably contributed to hypoxemia. The animals were restrained in lateral recumbency, this was done to facilitate instrumentation of the animal. Sternal recumbency is a preferable position, and should result in less hypoxemia.^1,8 Ruminal tympany probably contributed to hypoxemia. Hypoventilation was present with both combinations but was not severe (PaCO₂ was always <60 mm Hg). Hypoventilation tended to increase over time with MZT, perhaps as a result of ruminal tympany. Since hypoventilation was not severe, the major cause of hypoxemia was probably ventilation-perfusion mismatch. Increased ventilation-perfusion mismatch has been noted in sheep anesthetized with medetomidine-ketamine. Hypoxemia should respond to supplemental inspired oxygen, and supplemental oxygen is recommended with both of these treatments. When possible, the animal should be maintained in sternal recumbency, to decrease ventilation-perfusion mismatch and facilitate oxygenation.

Blood pressure was significantly higher with MZT. Medetomidine is more potent and selective for the alpha-2 receptor than xylazine. The increased blood pressure is most likely the result of peripheral alpha-2 receptor activation, produced by medetomidine.^1,9 BE and pH were both low in the early stages of immobilization. These values probably reflect increased muscle activity in the bison prior to immobilization. The animals were agitated at being handled and restrained in the chute. The decreased pH and BE may also have been the result of poor tissue perfusion early in the immobilization period. BE and pH improved over time as a result of decreased muscle activity, or increased perfusion. There was no respiratory compensation over time, in fact, the animals were experiencing a respiratory acidosis from the increase in PaCO₂.

Body temperature did not change over time. The mean temperature over time was 40.2°C with MZT and 40.3°C with XZT. This probably is a slight increase in temperature for this species and may reflect increased activity and stress during handling.

Ruminal tympany was never severe, nor was regurgitation a problem. In an unfasted animal, both of these complications have the potential to be more severe. Physical characteristics of immobilization suggest that XZT may be more useful for immobilization of game-farmed or captive animals. Currently, XZT would be the most economic combination, using our formulation it needs to be delivered at a relatively high volume, necessitating the use of larger, less accurate darts. Recovery is also more prolonged with XZT, this would not be a serious problem in a confined animal, but free-ranging animals may be at increased risk of predation. MZT can be delivered in a low volume, induction time is significantly lower than with XZT, but should still be suitable for most situations, recovery is significantly quicker than with XZT. Small volume and rapid recovery make this combination more attractive for free-ranging animals. The animals used in this study were free-ranging animals that were acutely confined for the purpose of this study and were unaccustomed to handling. Induction time may be shorter in game-farmed animals that are more accustomed to human manipulation. Antagonists were administered half IV and half IM. Several animals experienced full recoveries in less than 1 minute. Both atipamezole and tolazine are active IM, and IV administration is probably not advisable unless a safe location can be reached in less than 1 minute.

Conclusions

Both of these combinations will produce effective immobilization of bison. The major complication is hypoxemia. Supplemental oxygen is recommended, and maintenance in sternal recumbency should also be of some benefit, when possible. Recovery can be very rapid if the antagonists are administered IV, particularly following atipamezole administration. Intravenous administration of the antagonist should only be considered if a safe location can be reached quickly.

Acknowledgments

We thank Saskatchewan Agricultural Development Fund for funding this study. We also thank Rob Kaye, and Ron Larson (park wardens), the maintenance staff of Elk Island National Park, Dr. M.J. Limojes, and M. Read for assistance with this study. We thank the staff of the Fort Saskatchewan Hospital for assistance with the laboratory work, and we thank Orion Pharmaceuticals for the medetomidine and atipamezole used in this study.

Literature Cited

1.  Caulkett, N.A., T. Duke, and P.H. Cribb. 1996. Cardiopulmonary effects of medetomidine-ketamine in domestic sheep (Ovis ovis) maintained in sternal recumbency. J Zoo Wildl Med. 27:217–226.

2.  Caulkett, N.A., J.C. Haigh, and P.H. Cribb. 1995. Medetomidine-ketamine and carfentanil-xylazine in mule deer and mule deer hybrids. In: Proceedings of the ACVA annual meeting. Atlanta, GA. 43.

3.  Caulkett, N.A., W.J. Rettie, and J.C. Haigh. 1996. Immobilization of free-ranging woodland caribou (Rangifer tarandus caribou) with medetomidine-ketamine and reversal with atipamezole. In: Proc Amer Assoc Zoo Vet Annual Meeting, Puerto Vallarta, Mexico.

4.  Haigh, J.C., and C.C. Gates. 1995. Capture of wood bison (Bison bison athabascae) using carfentanil-based mixtures. J Wildl Dis. 31:37–42.

5.  Jalanka, H. 1989. Chemical restraint and reversal in captive markhors (Capra falconeri megaceros): a comparison of two methods. J Zoo Wildl Med. 20:413–422.

6.  Jalanka, H.H., and B.O. Roeken. 1990. The use of medetomidine, medetomidine-ketamine combinations, and atipamezole in non-domestic mammals: a review. J Zoo Wildl Med. 21:259–282.

7.  Kock, M.D., and J. Berger. 1987. Chemical immobilization of free-ranging North American bison (Bison bison) in Badlands National Park, South Dakota. J Wildl Dis. 23:625–633.

8.  Mitchell, B., and T.J. Williams. 1976. Respiratory function changes in sheep associated with lying in lateral recumbency and with sedation by xylazine. J Vet Anesth. 6:30–37.

9.  Vanio, O.M., B.C. Bloor, and C. Kim. 1992. Cardiovascular effects of a ketamine-medetomidine combination that produces deep sedation in Yucatan Mini Swine. Lab Anim Sci. 42:582–58.