Changes in production systems, increasing population, and increased demand for animal products have led to modifications in the diets ruminants consume. The use of antibiotics as growth promoters have become a necessity in modern cattle diets to prevent metabolic disorders and improve production efficiency. The extensive use of antibiotics in sub-therapeutic doses may be banned due to the observed increase in antibiotic-resistant microorganisms. Preliminary data suggest the use of antibodies can serve the same function as antibiotics (growth-promoting effects and prevention of metabolic disorders). More specifically, the use of avian-derived antibodies has been effective in reducing ruminal counts of target bacteria in steers fed high-grain diets. Replacing antibiotics with antibodies in cattle feed has long term advantages from a human health standpoint. The overall objectives of the experiments presented in this thesis were to evaluate the effects of avian-derived polyclonal antibody preparations on beef cattle performance, ruminal fermentation patterns, ruminai counts of target bacteria, and fecal shedding of E. coli O157:H7.