Zilpaterol HCl is a β-agonist feed additive approved in the United States to improve feed and growth efficiency of cattle, but its use is banned domestically and internationally in most food animal species and in human and animal competitive events. The objective of this study was to determine levels of zilpaterol exposure that would return positive results using qualitative and quantitative screening and analytical methods.  Sheep were fed 1.75 kg of feed containing 0.0075, 0.075, or 0.75 mg/kg of zilpaterol for 12 consecutive days. Urine and tissues were analyzed for zilpaterol residues. Zilpaterol was consistently detected by rapid screening assays (LOD = 1.7 ng/mL) in urine during the dosing and withdrawal periods. Rapid screening assays most consistently detected zilpaterol in tissues of animals exposed to the highest dose.  Urine of sheep exposed to 0.0075 mg/kg of dietary zilpaterol consistently tested positive by quantitative LC-MS/MS methods.

Urinary excretion and tissue residues of zilpaterol HCl after trace-level exposures

256th National Meeting (2018)

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