Abstract
In this article, key concepts important for enteric immunity are discussed. The gastrointestinal tract is the largest immune organ of the body. The mucosal barrier, the tight junctions and the "kill zone," along with the gut mucosa and maintaining an "anti-inflammatory" state are essential for "good gut health." The microbiome, the microorganisms in the gastrointestinal tract, which has more cells then the entire animal's body, is essential for immune development, immune response, and maximizing ruminant productivity. Direct-fed microbials aid in both microbiome stability "homeostasis" and immune function.