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.(ABSTRACT TRUNCATED AT 250 WORDS)