Simple Field Anesthesia for Free-Ranging Microtines

Abstract

Although physical restraint without anesthesia is a common way to immobilize microtines in field settings, tagging can cause pain and stress, and escape-response movements may reduce marking quality. To evaluate if inhaled isoflurane may be a tool to minimize these issues, we anesthetized free-ranging voles (Microtus and Myodes spp.) undergoing subcutaneous injection of a passive integrated transponder tag and dorsal fur clipping. We anesthetized 24 voles for short-duration anesthesia using two 0.2-mL isoflurane doses in a simple drop-chamber system. We used the first dose to induce unconsciousness and the second dose to immediately restore unconsciousness after the vole regained consciousness from the first dose. Median induction times were 54 s for the first dose (interquartile range [IQR], 47-61) and 50 s for the second dose (IQR, 38-55). Median recovery times were 33 s for the first dose (IQR, 26-60) and 62 s for the second dose (IQR, 35-104). No mortalities occurred during the holding period. The technique was simple, inexpensive, and effective. We therefore recommend using isoflurane delivered in a drop chamber when tagging or marking microtines in the field to improve handling.