Dietary fiber content influences small intestinal histomorphology and cecal microbial composition of laying hens

This study investigated the effect of increasing proportions (3%, 6%, 9%) of insoluble dietary fiber on small intestinal histomorphology and cecal microbial composition of Lohmann Tradition hens. At 21 weeks of age, 12 groups of 20 hens each were assigned to the three feeding treatments. The three diets were isocaloric and therefore differed in the proportions of main energy sources e.g. dietary fat. In week 65, three hens from each group were sacrificed to collect samples from the small intestine (duodenum, jejunum, ileum), and luminal and mucosal samples from the cecum. Villus height, villus width, and crypt depth were measured in the three small intestinal sections. Villus surface area and villus height-crypt depth ratio were calculated. Villus height and villus surface area increased with dietary fiber content in all three sections, indicating a potential increase in nutrient absorption in the small intestine with increasing fiber. With regards to cecal microbial composition, 16S rRNA gene amplicon sequencing was performed with the luminal and the mucosal samples to assess microbial diversity and relative abundances of bacterial genera. Our results showed that increasing fiber content increased the luminal alpha-diversity and shifted the microbial community structure at the genus level in both lumen and mucosa. A principal component analysis (PCA) of genus-level relative abundance data indicated that increasing fiber content was associated with an increased luminal abundance of butyrate-associated bacteria. In the mucosa, higher fiber content was associated with an increased abundance of mucosa-associated bacteria. Overall, insoluble fiber feeding of up to 9% was associated with beneficial changes in the small intestinal histomorphology and the cecal microbial composition, suggesting potential benefits for gut health. Despite the higher fat content in the 6% and 9% fiber diets, the increased fiber levels may have mitigated negative effects on gut health usually observed with high dietary fat.