Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/23/2006
Publication Date: 5/16/2006
Citation: Shelver, W.L., Smith, D.J. 2006. Tissue residue and urinary excretion of zilpaterol in sheep treated for 10 days with dietary zilpaterol. Meeting Abstract. Fifth International Symposium on Hormone and Veterinary Drug Residue Analysis Meeting, Antwerp, Belgium, May 16-19, 2006. Interpretive Summary:
Technical Abstract: Zilpaterol is a beta-adrenergic growth promoter approved for use in cattle in both Mexico and South Africa but not in the EU or the USA. Understanding the rates of zilpaterol depletion is necessary to develop appropriate strategies for zilpaterol detection. Eight sheep, fed 0.15 mg/kg/day dietary zilpaterol for ten days, were slaughtered in pairs 0, 2, 5, and 9 days after withdrawal from the zilpaterol-containing diet. Tissue zilpaterol levels rapidly decreased during the withdrawal period. Based on LC-MS/MS measurements, initial liver, kidney, and muscle zilpaterol levels were 30.4, 29.8, and 13.5 ng/g, respectively, and 98% of the zilpaterol was eliminated within 5 days. Urinary zilpaterol concentrations during the first 5 days of the withdrawal period followed a first order excretion pattern having an average elimination half life of 12.8 +/- 3.9 hrs. Comparison of concentrations determined using ELISA, HPLC, and LC-MS/MS with external standard calibration showed a high correlation with each other. The regression coefficients were generally within 15-20% of 1.00 indicating the near equivalence of the methods. Because of its simplicity, ELISA is a convenient assay for determining zilpaterol levels in urine and has similar levels to HPLC and LC-MS/MS without requiring the extensive cleanup of the latter methods.