The effect of microbiome modulation on the intestinal health of poultry

The chicken gastrointestinal (GI) tract is home to a complex microbial community that underlines the links between diet and health. The GI tract is rich in microbial biodiversity, playing home to >= 500 phylotypes or similar to 1 million bacterial genes, which equates to 40-50 times the number in the chicken genome. Manipulating the microbiota would serve as promising therapeutic paradigm; albeit not a new concept for the poultry industry as evidenced by competitive exclusion where newly hatched chickens could be protected against colonization by Salmonella enteritidis by dosing a suspension of gut contents derived from healthy adult chickens. This concept of adding beneficial bacteria to the intestine has led to the development of probiotics and prebiotics. Unlike the host genome, which is rarely manipulated by xenobiotic intervention, the microbiome is readily changeable by diet, ingestion of antibiotics, infection by pathogens and other host- and environmental-dependent events. The plasticity of the microbiome has been implicated in numerous disease conditions, and an unfavorable alteration of the commensal structure of gut microbiota is referred to as dysbiosis; this includes a reduction in the number of tolerogenic bacteria and an over-growth of potentially pathogenic bacteria (pathobionts) that can penetrate the intestinal epithelium and induce diseases in certain genetic or environmental contexts. This review highlights the plasticity of the avian microbiome that allows defined interventions as a means of enhancing poultry health and productivity. The ability to intentionally manipulate the microbiota by providing nutrients, modulating host immunity, inhibiting/preventing pathogen intestinal colonization, or improving intestinal barrier function has led to a number of novel methods to prevent disease, but also led to improved body weight, feed conversion, and carcass yield.