Immobilization of muskrats (Ondatra zibethicus) with ketamine and xylazine

The effectiveness of ketamine and xylazine as an immobilizing combination for muskrats (Ondatra zibethicus) was evaluated. Eleven muskrats were intramuscularly injected using a high (n = 7) or low (n = 4) dosage of a 20:1 mixture of ketamine (12 or 20 mg) and xylazine (0.6 or 1.0 mg) in Carlton County, Minnesota (USA) from 1 to 4 May 1995. Mean (+/- SD) induction times for muskrats receiving a high dosage (6.5 +/- 2.6 min) or low dosage (7.0 +/- 1.6 min) was similar (P = 0.71). In contrast, muskrats receiving a low dosage recovered sooner (37.0 +/- 15.1 min) than muskrats receiving a high dosage (62.2 +/- 15.6 min) (P = 0.04). There was a positive linear relationship (r2 = 0.75, P = 0.02) between the amount (mg/kg) of ketamine-xylazine injected and recovery time but not between the amount injected and induction time (r2 = 0.49, P = 0.18). Heart rate, respiratory rate, and body temperature were similar (P = 0.20 to 0.62) between high and low dose groups. No mortality occurred nor were short-term adverse effects observed in recaptured individuals. I conclude that a 20:1 mixture of ketamine-xylazine is a safe and effective immobilization agent for muskrats when conducting non-surgical field procedures. Immobilizing muskrats with 15 mg/kg ketamine and 0.75 mg/kg xylazine should provide about 10 min of handling time before arousal and allow full recovery in < 60 min.