Ketamine-Butorphanol-Azaperone-Medetomidine for Helicopter Capture of Free-Ranging Caribou (Rangifer tarandus) in Alaska, USA.

Abstract

Caribou (Rangifer tarandus) are frequently captured for research and management, often using drug combinations that include potent opioids. We evaluated an alternative combination of butorphanol-azaperone-medetomidine (BAM) plus ketamine (KBAM) for helicopter-based captures of free-ranging caribou. The study included 61 animals from four herds captured between October 2024 and April 2025: 30 female calves and 31 adult cows. Initially, 11 calves were immobilized with 1 mL BAM and 50 mg ketamine; subsequently, the ketamine dose was reduced to 30 mg for the remaining calves. Adult cows received 1.75-2.25 mL BAM with 50 mg ketamine. Overall, 22/30 calves were weighed, and doses (mean ±SD [range]) were 0.51±0.04 (0.43-0.60) mg/kg for butorphanol, 0.17±0.01 (0.14-0.20) mg/kg for azaperone, and 0.21±0.01 (0.17-0.24) mg/kg for medetomidine. Mean ketamine doses were 0.96±0.08 (0.85-1.10) mg/kg for calves receiving 50 mg and 0.55±0.04 (0.48-0.63) mg/kg for calves receiving 30 mg. Mean time from darting to recumbency was 4.1 min (range 2-8 min) for calves and 6.3 min (range 3-16 min) for adults, and mean time from intramuscular reversal with atipamezole and naltrexone to standing was 5.4 min (range 1-12 min) for calves and 6.0 min (range 1-38 min) for cows. No capture-related mortalities were observed within 1 mo post-release. All animals experienced hypoxemia, which improved with intranasal oxygen administration. These results suggest that KBAM is an effective alternative to potent opioids for helicopter-based capture of caribou, providing reasonably rapid induction and recovery while minimizing mortality risk.

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