Chemical capture of free-ranging cattle: Immobilization with xylazine or medetomidine,and reversal with atipamezole

Twenty-nine free-ranging Norwegian cattle were captured with xylazine (n=20) or medetomidine (n=9) using a tranquilizing gun, and the time from darting to recumbency (induction time) was recorded. Twenty-eight animals were given atipamezole IV 15–100 min after darting, and the effects of the antagonist were evaluated. Blood samples (n=19) for haematology and serum chemistry were collected within 10 min after immobilization was induced.Xylazine (0.55±0.18 mg/kg; mean ± SD;n=18) or medetomidine-HCl (0.039±0.10 mg/kg;n=8) induced complete immobilization after a single darting with sternal or lateral recumbency, the induction times being 9.6±3.8 and 12.0±6.8 min, respectively. No difference in the clinical effects of the two drugs was observed.Rapid reversal was achieved with 0.057±0.017 and 0.077±0.019 mg/kg of atipamezole-HCl in xylazine- and medetomidine-treated animals, respectively. All the animals stood within 2 min after IV administration of the antagonist. Seven animals showed signs of excitement shortly after reversal, but these side-effects were of brief duration. Heavy resedation with relapse into recumbency was seen 3–4 h after reversal in two cows captured with xylazine, while moderate resedation was observed in two medetomidine-treated animals 2 h after reversal.Except for the plasma glucose concentration, which was elevated in both xylazine- and medetomidine-treated animals, the mean values of the haematological and plasma chemical parameters were within the reference ranges established for Norwegian cattle.Eight cows captured with xylazine (0.51±0.20 mg/kg) and given atipamezole-HCl (0.045±0.013 mg/kg) for reversal were in the last two months of pregnancy. All these animals calved normally and no cases of premature births or other periparturient disorders were seen.Abbreviations EDTA ethylene diamine tetraacetic acid - IM intramuscular - IV intravenous - SC subcutaneous - SD standard deviation