Antagonism of xylazine sedation in steers by doxapram and 4-aminopyridine.

Five groups of 6 fasted crossbred steers were injected IM with standard dosages of xylazine hydrochloride (0.3 to 0.5 mg/kg). At maximal sedation, the steers were injected IV with the antagonists' doxapram (1.0 mg/kg), doxapram + yohimbine (0.125 mg of yohimbine/kg), doxapram + 4-aminopyridine (4-AP; 0.3 mg of 4-AP/kg), or 4-AP + yohimbine. One group was given 1.0 ml of saline solution IV instead of antagonists. Doxapram, doxapram + yohimbine, doxapram + 4-AP, and 4-AP + yohimbine decreased mean standing time (time from antagonist injection until animal could stand unaided) to 17.0, 4.3, 3.3, and 4.5 minutes, respectively--significantly (P less than 0.05) down from a control value of 49.8 minutes. Mean total recovery time (time from xylazine injection until animal resumed eating) was decreased to 78 minutes by doxapram and 81.6 minutes by doxapram + 4-AP--significantly (P less than 0.05) down from the control value of 142.9 minutes. Respiratory character was improved (depth of respiration was increased) only by doxapram + 4-AP. Relapses to recumbency and marked sedation were not seen in steers given doxapram + 4-AP or the saline solution. One steer given doxapram, 2 given doxapram + yohimbine, and 1 given 4-AP + yohimbine relapsed to recumbency and sedation. Recovery was relatively smooth in steers given doxapram + 4-AP or 4-AP + yohimbine. Animals given doxapram or doxapram + yohimbine had difficult recoveries.(ABSTRACT TRUNCATED AT 250 WORDS)