Abstract

The purpose of this study was to compare the cardiopulmonary, metabolic and anesthetic effects of carfentanil-xylazine and etorphine-xylazine combinations in rhebok (Pelea capreolus), a species of South African antelope that is rarely maintained in captivity. Twelve adult rheboks were immobilized using a combination of 0.4 mg/kg xylazine and either 0.01 mg/kg of carfentanil (n=6) or 0.01 mg/kg etorphine (n=6), delivered intramuscularly using a remote injection system. Induction and recovery times, heart rate, respiratory rate, rectal temperature, oxygen saturation (SPO₂), end-tidal CO₂, anesthetic depth, indirect blood pressures, and arterial blood gases were recorded. Rheboks were not intubated, but nasal oxygen was administered. Anesthesia was antagonized with naltrexone (100 mg naltrexone/1 mg opioid) and yohimbine (0.25 mg/kg), one-half dose administered intravenously and one-half dose administered subcutaneously, approximately 40 minutes after induction. Mean initial heart rates were significantly higher in the carfentanil group than in the etorphine group. During the first 7–10 minutes of anesthesia in both groups, arterial pH decreased, while SPO₂, pO₂ and pCO₂ (pCO₂) increased. These findings were consistent with respiratory acidosis associated with decreased ventilation. Initially, rheboks in the carfentanil group were more responsive to stimuli than rheboks in the etorphine group. Time to first arousal was significantly shorter in the etorphine group (1.3 minutes) than in the carfentanil group (7.6 minutes). Although there were few statistical differences between quantitative data of the two groups, qualitative aspects of the two regimens demonstrated notable differences. Rheboks in the carfentanil group were at a comparatively lighter degree of immobilization, and some required additional manual and chemical restraint. In conclusion, 0.01 mg/kg of etorphine and 0.4 mg/kg of xylazine is recommended over 0.01 mg/kg carfentanil and 0.4 mg/kg xylazine due to qualitatively better anesthetic episodes and shorter recovery times.