Interactions between Dietary Chicory, Gut Microbiota and Immune Responses

This thesis provides a better understanding of interactions between diet, gut microbiota, and immune responses to a specific dietary fiber source, chicory (Cichorium intybus L). This was achieved by examining the impact of chicory fiber on animal performance, digestibility, gut development, commensal bacteria community structure in small and large intestine, and follow-up reactions with specific immune components, cytoprotective heat shock protein (HSP) 27 and 72, in vivo and in vitro. The impacts of dietary chicory on nutrient utilization, performance, and gut environment and morphology were investigated in chickens and young pigs. One-dayold chicks were fed cereal-based diets with inclusion of 60 or 120 g/kg chicory forage and/or root, with each forage diet derived from two harvests. Growing pigs were fed diets without and with inclusion of 80 or 160 g/kg chicory forage and/or root. The results showed that chicory inclusion maintained good animal performance and was accompanied by changes in gut morphology. Total tract apparent digestibility of nonstarch polysaccharides (NSP) and uronic acid in broilers decreased with inclusion of 120 g/kg chicory, but not with inclusion of 60 g/kg. This indicates that chicory can be used as a palatable fiber source for broiler chickens and young pigs. Gut microbiota complexity and dietary NSP-induced changes in pigs were examined using terminal restriction fragment length polymorphism (T-RFLP). The analysis revealed four primary microbiota clusters: luminal and mucosal ileal microbiota and luminal and mucosal colonic microbiota. In the ileum, lactic acid bacteria (LAB) were dominant and responsive to inulin-type fructan. In the colon, bacteria belonging to clostridial cluster IV and XIVa responded to chicory pectin, whereas Prevotella was related to cereal xylan. Mapping of cytoprotective HSP27 and HSP72 occurrence in porcine gut revealed regionand cell type-specific features. Physiological expression of HSP72 was correlated with LAB, representing an important interplay between HSPs and commensal microbes. In-depth studies of interactions between lactobacilli and gut mucosa and their effects on barrier function and HSP expression revealed protective effects from lactobacilli by enhancing HSP and tight junction protein expression under pathogen challenge.