Effect of yohimbine on xylazine-induced immobilization in white-tailed deer

Two groups of white-tailed deer were given IM injections of xylazine with a projectile syringe. Deer in one of the groups served as controls and did not receive any treatments other than xylazine. Deer in the other group were given yohimbine IV at various times (15 to 171 minutes) to evaluate its effect on xylazine-induced immobilization. In 5 control deer given 3.7 +/- 1.2 mg of xylazine/kg (mean +/- SD), onset of recumbency was 13 +/- 2 minutes and time to standing was 268 +/- 76 minutes. In 20 principal deer given 2.8 +/- 1.0 mg of xylazine/kg, onset of recumbency was 8 +/- 7 minutes, time to sitting after giving yohimbine was 3 +/- 4 minutes in 18 of the deer, and time to standing after giving yohimbine was 4 +/- 5 minutes in 19 of the deer. Most of these deer were still moderately sedated 30 minutes after injection of yohimbine, but none of them became reimmobilized or as deeply sedated as before the injection of yohimbine. Yohimbine also reversed the bradycardia and respiratory depression induced by xylazine.