Influence of β-Agonists (Ractopamine HCl and Zilpaterol HCl) on Fecal Shedding of Escherichia coli O157:H7 in Feedlot Cattle

Ractopamine HCl and zilpaterol HCl, β-agonists recently approved for use in feedlot cattle to improve performance traits and carcass leanness, were examined for their effects on fecal shedding of Escherichia coli O157:H7 in feedlot cattle. Fecal samples (n = 2,454) were obtained from four experiments (one ractopamine HCl, three zilpaterol HCl) over the course of a 3-year period, either by rectal palpation (ractopamine HCl experiment) or from pen-floor fecal pats. Samples were cultured quantitatively and qualitatively for E. coli O157:H7. No significant treatment differences were detected for fecal prevalence of E. coli O157:H7 in the ractopamine HCl experiment. Zilpaterol HCl feeding had no effect (P > 0.20) on fecal shedding in the first or second experiments, with overall E. coli O157:H7 prevalence relatively low (