REVERSAL OF XYLAZINE-INDUCED SEDATION IN DAIRY CALVES WITH ATIPAMEZOLE - A FIELD TRIAL

Dairy calves immobilized with xylazine (XYL) were given atipamezole-HC l (ATI) at different XYL:ATI dose ratios (w/w) for reversal and the an tagonistic 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 ani mals (n = 195) and there were no spontaneous recoveries before injecti on of atipamezole or saline. Atipamezole was given 10-81 min and salin e 25 min after xylazine administration. Intramuscular administration o f 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-indu ced immobilization and sedation. The mean times (standard deviation) f rom 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 anima ls (n = 11) was 94.1 (3.0) min. Intravenous administration of atipamez ole 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 dos e 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. The mean time to standing for cont rol animals (n = 14) was 88.1 (13. 1) min. Animals given high doses of atipamezole (dose ratio groups 5:2 intramuscularly, 10:3 intravenousl y and 4:1 intravenously) showed signs of excitement while in animals g iven low doses of atipamezole (dose ratio groups 5:1 intramuscularly a nd 10:1 intravenously) resedation and relapse into recumbency occurred . Medium doses of atipamezole (dose ratio groups 10:3 intramuscularly, 4:1 intramuscularly, 5:1 intravenously and 8:1 intravenously) did not cause any undesirable side-effects or resedation, and can be recommen ded for reversal of xylazine-induced sedation in dairy calves