A Mixture of Butorphanol, Azaperone, and Medetomidine for the Immobilization of American Beavers (Castor canadensis)

A total of 58 American beavers (Castor canadensis) was immobilized with butor-phanol, azaperone, and medetomidine (BAM) for the purpose of health assessments, sex determination, and placement of very high-frequency tail transmitters in a subset of animals. Isoflurane gas anesthesia was available to aid with induction when needed, and all animals received supplementary oxygen. Thirty-one beavers immobilized with a mean (SD) dose of 0.65 (0.15) mg/kg butorphanol, 0.22 (0.05) mg/kg azaperone, and 0.26 (0.06) mg/kg medetomidine did not require supplemental isoflurane during induction and the mean induction time was 8 min (range: 3-21 min). This dose was equivalent to 0.024 (0.005) mL of BAM per kilogram. A total of 29 beavers that were immobilized with a mean (SD) of 0.51 (0.07) mg/kg butorphanol, 0.17 (0.02) mg/kg azaperone, and 0.2 (0.03) mg/kg medetomidine needed supplementary isoflurane at 5% and 5 L/min for < 1 min to induce full anesthesia. In none of the beavers did BAM alone provide sufficient depth of anesthesia to drill a hole in the tail for transmitter placement, and supplementary isoflurane was administered to reach a sufficient level of analgesia for the procedure. The beavers were reversed with 5 mg of atipamezole per milligram of medetomidine and 1 mg of naltrexone per milligram of butorphanol. No adverse effects or mortalities were observed. Butorphanol-azaperone-medetomidine can be considered safe for use in American beavers for minor procedures.