Intestinal microbiota and metabolites-Implications for broiler chicken health and performance

Microbiota in the intestine of an animal species has evolved together with the host. This coevolution has produced specific host-microbe combinations, called superorganisms, with the best possible fitness in a given environment. Intestinal microbiota has an enormous metabolic potential and it affects both the nutrition and health of the host. The importance of intestinal microbiota for the performance of broiler chickens has been studied for decades. The microbial community structure of the cecum is significantly more complex and less well characterized than that of the crop and small intestine. Culture-independent molecular techniques have recently been introduced to bring fresh insights into the intestinal system of the broiler chicken. As a consequence, there is growing evidence of connection between the apparent metabolizable energy of the diet and microbiota composition in the hindgut of the host. This connection can be due to direct conversion of some dietary components into high-energy metabolites by specialized bacteria. The utilization of such fermentation end products would provide more energy for the host, which could be measured as improved feed conversion efficiency. However, it is also possible that cecal microbial profile is a reflection of feed digestion and nutrient absorption efficiency in the proximal intestine. Disorders in these functions cause excess nutrient bypass to the lower intestine, providing new, easily available substrates for bacteria that could otherwise not compete in that habitat. The 2 causal links described are likely to coexist in real life situations, but their relative dominance warrants further well-designed studies.