Reversal of xylazine-induced sedation in dairy calves with atipamezole: a field trial.

Dairy calves immobilized with xylazine (XYL) were given atipamezole-HCl (ATI) at different XYL:ATI dose ratios (w/w) for reversal and the antagonistic effect of xylazine was evaluated. Control animals received saline for comparison. Intramuscular administration of xylazine (0.139-0.357 mg/kg) induced sedation with complete immobilization in all animals (n = 195) and there were no spontaneous recoveries before injection of atipamezole or saline. Atipamezole was given 10-81 min and saline 25 min after xylazine administration. Intramuscular administration of atipamezole at XYL:ATI dose ratios of 5:2 (n = 11), 10:3 (n = 21), 4:1 (n = 21) and 5:1 (n = 25) effectively antagonized the xylazine-induced immobilization and sedation. The mean times (standard deviation) from injection of atipamezole until the animals were standing for these dose ratio groups were 6.09 (3.12), 5.15 (2.87), 6.35 (2.54) and 7.86 (3.11) min, respectively. The mean time to standing for control animals (n = 11) was 94.1 (3.0) min. Intravenous administration of atipamezole at XYL:ATI dose ratios of 10:3 (n = 7), 4:1 (n = 33), 5:1 (n = 16), 8:1 (n = 27) and 10:1 (n = 9) rapidly reversed the xylazine-induced immobilization and sedation. The mean times (standard deviation) from injection of atipamezole until the animals were standing for these dose ratio groups were 0.98 (0.22), 1.32 (0.48), 1.09 (0.34), 1.39 (0.52) and 1.60 (0.69) min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)