The specific objective of this proposal is to assess the temporal changes in the cecal microbiome of broiler chickens that drive changes in C. jejuni loads. We will conduct a prospective cohort study in which farms that raise broilers to normal age (6 weeks) or older (9 weeks) will be enrolled. C. jejuni loads will be tracked weekly, and the cecal microbiome of birds on these farms will be assessed weekly. We expect to observe a temporal association between cecal microbiome diversity and cecal C. jejuni dynamics, with the identification of specific changes in bacterial communities preceding C. jejuni colonization and clearance. Identifying organisms associated with the decline of C. jejuni would provide potential targets for probiotics to control C. jejuni colonization in broiler chickens.