Use of methoxyfluorane to surgically implant transmitters in muskrats

We tested the feasibility of using methoxyflurane as a field anesthetic on 12 adult muskrats (Ondatra zibethicus) from May through September 1987. Transmitters were successfully implanted into the peritoneal cavity of 8 muskrats. Following release, these animals were monitored for <163 days. Methoxyflurane was adequate as a field anesthetic for use on muskrats, but induction (f = 20 min) and recovery (2 = 2 hr) times were longer than those reported for smaller rodent species. J. WILDL. MANAGE. 53(2):331-333 Implanted radio transmitters have been used to monitor behavior of several species of aquatic and semi-aquatic mammals (Melquist and Hornocker 1979, Garshelis and Siniff 1983, Davis et al. 1984, Eagle et al. 1984), but information on the use of radio transmitters in muskrats is limited. MacArthur (1978, 1979) and MacArthur and Aleksiuk (1979) implanted transmitters into the abdominal cavity of muskrats to examine seasonal body temperature profiles and winter home range, but they provided no information on surgical procedures or effectiveness of the anesthetic employed. We used radio-transmitter implants to monitor muskrat movements and to locate muskrat burrows in peat banks, at 3 sites in Clinton County, New York. Ketamine hydrochloride (Parker and Maxwell 1980) and sodium pentobarbital (MacArthur 1978, 1979; MacArthur and Aleksiuk 1979) have been used in field studies of muskrats; the latter drug has been used to permit surgery. Neither of these was considered desirable for our purposes. Ketamine can induce convulsions requiring the use of sedatives or tranquilizers to ameliorate the condition (Fowler 1978). Sodium pentobarbital has a narrow safety margin requiring carefully measured amounts to prevent overdose (Muir et al. 1986). Methoxyflurane, an inhalant anesthetic, has a wide safety margin and few complicating side effects (Byles and Dobkin 1971, Muir et al. 1986). Methoxyflurane has been applied in field studies of smaller rodents (Barry 1972, Smith and Whitney 1977, Hardy and Taylor 1980, Vogt et al. 1983, Eagle et al. 1984), but more comparative data are eeded to assess the potential of this anesthetic for use on other free-ranging mammals. We report on the use of methoxyflurane as a field anesthetic and include a procedure for surgically implanting radio transmitters into the peritoneal cavity of muskrats. We thank K. B. Adams for helpful advice and logistic support. This research was supported by a Theodore Roosevelt Memorial Fund Grant, the Research Foundation of the State University of New York, the Pennsylvania State University, the William H. Miner Agricultural Research Institute, the Department of Biological Sciences of the State University College at Plattsburgh, and a private donation from P. Blahey and fam-