Ketamine-medetomidine or isoflurane immobilization of black-footed ferrets

Field immobilization of black-footed ferrets (Mustela nigripes) is required for examination, identification, and attachment of radiocollars, but ferrets must completely recover from anesthesia prior to release. We evaluated 2 anesthetic regimes: (1) a combination of ketamine (KET) and medetomidine (MED) with antagonism by atipamezole (ATI), and (2) isoflurane (ISO) gas anesthesia delivered by a portable anesthetic system. We used hybrid surrogates in dose titration trials for both MED-KET and ISO anesthesia and developed an intramuscular dose of 0.075 mg/kg MED and 3.0 mg/kg KET, or a maintenance ISO concentration of ≥3%. The initial dose of MED-KET induced anesthesia in 11 of 14 ferrets in 7.5 ± 1.6 min (x̄ ± SE); boosters of 1.5 mg/kg KET were required to induce anesthesia in the other 3 ferrets in 12.3 ± 1.3 min. Recovery time after administration of ATI was 6.9 ± 0.6 min. Isoflurane induced anesthesia in 1.1 ± 0.1 min and recovery occurred 16.3 ± 1.4 min after cessation of ISO. Compared to MED-KET, ferrets anesthetized with ISO had faster induction times, slower arousal times, slower recovery times, higher oxygen saturation$(\text{SpO}_{2})$, higher heart rate (HR), and higher body temperature (BT). Field trials confirmed that ferrets can be effectively and safely immobilized with MED-KET or ISO. Ferrets appeared more physiologically normal under ISO anesthesia, although there was no evidence of adverse effects from the use of MED-KET. With either anesthetic regime, biologists are cautioned to monitor ferrets throughout anesthesia for both hypothermia and respiratory depression.