Campylobacter jejuni infections in humans continue to be a major cause of bacterial gastroenteritis in the U.S. Most cases have been associated with poultry handling, poultry product consumption or cross-contamination. C. jejuni colonizes the chicken gut after the decline of the passive humoral immune response, and the chickens seem to be unable to clear the infection during their production lifespan. This proposal will investigate the complex microbial interactions that occur in the cecal microbiome with the goal of designing targeted interventions that make the cecum an unfavorable environment for C. jejuni colonization. The specific objectives are:1.- Determine the effects of interventions targeting the gut microbiome on the colonization dynamics of C. jejuni in broiler chickens. We will quantify the effects of the interventions on the alpha diversity, beta diversity, and differential bacterial abundance of the cecal and broiler house (litter) microbiomes and evaluate the effects of interventions on the humoral immune response (IgA and IgY) as potential mediators in the causal pathway between the interventions and the colonization dynamics of C. jejuni in broiler chickens.2.- Estimate the impact of interventions targeting the gut microbiome in reducing the load of C. jejuni on broiler carcasses using a system dynamics approach. We will modify a broiler house system dynamics model that we have previously developed to estimate the efficacy and costs of interventions targeting the gut microbiome in broiler chickens.