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

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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 (<7%). In the third zilpaterol HCl experiment, the percentage of fecal samples that were E. coli O157:H7 positive following qualitative culture was higher (P < 0.05) in the zilpaterol HCl treatment (10.3%) than for the control (6.1%). The current research showed minimal effects of β-agonists on fecal shedding of E. coli O157:H7 and indicated that these compounds (fed immediately prior to slaughter) are not a cause for concern from a food safety standpoint.

Document Type: Research Article

Affiliations: 1: Food and Feed Safety Research Unit, Agricultural Research Service, U.S. Department of Agriculture, College Station, Texas 77845, USA. 2: Food and Feed Safety Research Unit, Agricultural Research Service, U.S. Department of Agriculture, College Station, Texas 77845 3: Department of Agricultural Sciences, West Texas A&M University, Canyon, Texas 79016 4: Cactus Feeders, Inc., Amarillo, Texas 79116 5: Southeast Colorado Research Center, Colorado State University, Lamar, Colorado 81052 6: Elanco Animal Health, Greenfield, Indiana 46140 7: Intervet/Schering-Plough Animal Health, De Soto, Kansas 66018 8: Desert Research and Extension Center, University of California, El Centro, California 92243, USA

Publication date: December 1, 2009

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