Efficacy of a Butorphanol, Azaperone, and Medetomidine Combination for Helicopter-Based Immobilization of Bison ( Bison bison).

Decreased access to potent narcotics for wildlife applications has stimulated the need to explore alternative drug combinations for ungulate immobilizations. A combination of butorphanol, azaperone, and medetomidine (BAM) has been used for some ungulate species, but information on its use in bison ( Bison bison) is limited. We conducted field trials using BAM, in conjunction with atipamezole and naltrexone as antagonists, for reversible field immobilization of bison during ground- and helicopter-based operations. We compared times to induction and recovery, vital rates (rectal temperature and respiration rate), and the quality of induction, immobilization, and recovery between ground- and helicopter-based immobilizations of bison. Overall, 15 of 21 bison were induced with the volume we used (mean±SD=3.4±0.6 mL); two other animals darted from a helicopter required a full second dose, and four others (two darted from the ground and two from a helicopter) required a supplemental partial dose to achieve induction. All immobilizations achieved a sufficient plane of anesthesia to permit minor invasive procedures (e.g., skin biopsy and blood sampling). All animals recovered, and most (17 of 21) were reversed in ≤5 min. The mean time to induction was 10.8±7.3 min while that for recovery was 5.0±2.1 min. We found few differences in vital rates or the quality of immobilizations between ground- and helicopter-based captures. The drug combination provided good immobilization and was reliably reversed; however, inconsistent inductions at the doses we used may limit its use in field immobilizations of bison, particularly those animals being darted from a helicopter.