Bison are becoming increasingly popular as a game farmed species. Reliable immobilization is often difficult and usually requires use of potent opioids. Many wildlife managers and veterinarians are unwilling to handle potent opioids due to safety concerns. The objective of this study was to develop effective, “user friendly” alternatives to opioid immobilization. Seven wood bison, with an average weight of 413 ± 35 kg were used in this study. The bison were fasted 24 hours prior to immobilization. On the day of the study the bison were restrained in a hydraulic chute, weighed, and hand injected in the gluteal muscle mass with 1.5 mg/kg of xylazine + 3 mg/kg of Telazol® (XZT) or 60 ug/kg of medetomidine + 1.2 mg/kg of Telazol® (MZT). The average drug volume required was 7 ml with XZT and 2.78 ml with MZT. Each animal received both treatments one week apart. Immediately following immobilization the animal was placed in lateral recumbency and a 20 gauge, 5 cm catheter was placed in the saphenous artery for direct pressure measurement and withdrawal of arterial blood samples. Lead II ECG was constantly monitored. HR, RR, direct BP, and temperature were recorded every 5 minutes. PaCO2, PaO2, BE, and pH were measured every 15 minutes. Sixty minutes post-drug administration atipamezole, 90 ug/kg IV and 90 ug/kg IM, was administered to antagonize medetomidine. Tolazoline was administered at a dose of 1.5 mg/kg IV + 1.5 mg/kg IM to antagonize xylazine. Physiological measurements were compared between treatments with 2 way ANOVA for repeated measures and over time with a one way ANOVA for repeated measures. Immobilization characteristics were compared with a paired t-test (P < 0.05). Induction was significantly faster with XZT (4.1 ± 0.97 minutes) compared to 7.5 ± 2.11 minutes (mean ± SD) with MZT. Recovery following antagonist administration was significantly faster with MZT, 1.7 ± 0.82 minutes, compared to XZT, 11.8 ± 9.65 minutes. Comparison between treatments revealed significantly higher MAP and RR with MZT and significantly higher PaCO2 with XZT. The major complication of both combinations was hypoxemia with the lowest PaO2 of 46.9 ± 7.6 mmHg occurring at 45 minutes post-injection with MZT and the lowest PaO2 of 44.4 ± 5.3 mmHg occurring at 30 minutes post-injection with XZT. Mild ruminal tympany was observed with both combinations. Spontaneous recovery was faster with XZT, some animals were moving limbs or head at 55 minutes post-injection. Both of these combinations will produce effective immobilization of bison. The lower drug volume with MZT increases its utility if remote delivery is required. Animals receiving these combinations should receive supplemental inspired oxygen.
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