Technical Abstract: Foodborne pathogenic bacteria such as E. coli O157:H7 are threats to the safety of beef and are publically perceived as “hamburger diseases.” Fresh citrus peel and dried orange pulp are by-products from citrus juice production that have a relatively high nutritive value (high TDN). Orange peel and pulp is available at low prices in citrus-producing regions and is thus often incorporated into least-cost ration formulations for beef and dairy cattle. Because of the natural antimicrobial effects of orange peel/pulp, it has been proposed for use as a low-cost feed ingredient that could be used to decrease foodborne pathogenic bacteria populations in cattle. We have previously reported that orange peel and pulp reduced (P < 0.05) populations of E. coli O157:H7 and Salmonella in mixed ruminal fluid fermentations in the laboratory and reduced growth rate (P < 0.05) and final populations (P < 0.05) of pathogens in pure culture studies. Therefore, this study was designed to determine if the antipathogenic effects of orange peel and pulp were effective against E. coli O157:H7 in vivo. Sheep (n = 24) were fed a cracked corn grain-based diet that was supplemented with a 50%/50% mixture of dried orange pellet and fresh orange peel to achieve a final concentration (DM basis, w/w) of 0%, 5%, or 10% pelleted orange peel for 7 d. Following this adaptation period, sheep were artificially inoculated with 1010 CFU E. coli O157:H7 by oral dosing. Fecal shedding of E. coli O157:H7 was measured daily for 5 d before animals were humanely sacrificed, and it was reduced (P < 0.05) in sheep fed 10% OP after 96 hrs post-inoculation. Populations of inoculated E. coli O157:H7 were reduced by OP treatment throughout the gastrointestinal tract; however, this reduction reached significant levels in the rumen (P < 0.05) of sheep fed 10% OP diets. Cecal and rectal populations of E. coli O157:H7 were reduced (P < 0.05) by inclusion of both 5% and 10% OP diets. Our results demonstrate that orange peel products are environmentally friendly and low-cost products that can be used as a pre-harvest intervention as part of an integrated pathogen reduction scheme.