Comparison of Intramuscular Ketamine–Medetomidine, Ketamine–Dexmedetomidine and Ketamine–Xylazine for Immobilization of Captive Rhesus Macaques (Macaca mulatta)

Anesthesia protocols in laboratory-held rhesus macaques (Macaca mulatta) are well described, but fewer reports exist in zoo, safari park or field environments. This study recorded and compared the level of sedation, heart rate (HR), respiratory rate (RR), and induction and recovery times of ketamine–medetomidine (KM), ketamine–dexmedetomidine (KD) and ketamine–xylazine (KX) protocols in ninety-five safari-park-managed rhesus macaques. In total, 31 animals received the KM protocol, which included 25 mg ketamine (6.08 ± 1.54 mg/kg) and 0.15 mg medetomidine (0.04 ± 0.01 mg/kg); 33 animals received the KD protocol, which included 25 mg ketamine (6.19 ± 2.42 mg/kg) and 0.08 mg dexmedetomidine (0.02 ± 0.01 mg/kg); and 31 animals received the KX protocol, which included 50 mg ketamine (12.64 ± 3.79 mg/kg) and 1.2 mg xylazine (0.30 ± 0.09 mg/kg). Anesthesia was reversed with atipamezole. The mean bodyweight of the study population was lower than expected, so actual doses were higher than intended; no adverse effects were reported. Induction and recovery times were longer for KX than KD or KM (p < 0.05) but did not differ significantly between KD and KM (p > 0.05). HR and RR did not differ between protocols (p > 0.05). Sedation score was negatively correlated with bodyweight, and mean sedation score was lower for KX than KM or KD. KD and KM provided more rapid and reliable sedation than KX at the doses described; however, alterations in the KX dose may improve reliability.