Host-microbiome interactions

Diets based on large amounts in starch and low in fibre increase the risk of ruminal acidosis with major consequences for rumen microbiome and the host health. The inclusion of energy-rich hay has recently been suggested as an alternative to starch-rich diets. The aim of this research was to quantify the effect of titrated levels of high energy, high fibre hay (high quality hay; HQH) on the rumen epimural bacterial population, ruminal pH and epithelial gene expression targets for barrier function and metabolism. Eight ruminally cannulated non-lactating and non-pregnant Holstein cows were used in a replicated 4x4 Latin square design with three of the four dietary treatment groups containing high-quality hay (HQH), with either 0% concentrate (100% HQH), 25% concentrate (75% HQH) or 40% concentrate (60% HQH). The fourth group (CON), considered as control treatment, was fed with 60% normal fibre-rich hay and 40% concentrate. Samples of rumen papillae for both microbiota and gene expression were taken in each run. Measures of diversity for the rumen epithelial population, specifically Shannon (P = 0.004)and Simpson (P = 0.003) indices decreased with increasing levels of HQH in the diet. A number of Gram-negative genera including Anaerovibrio, and Selenomonas were found to be increased in relative abundance in the 60HQH diet. Campylobacter and Methanosphaera spp. were highest in the 100HQH diet. The substitution of sugar rich HQH in place of starch rich concentrates in high producing animal diet in this experiment showed no effects on nutrient transport, pH regulation, pattern-recognition receptor, and barrier function gene expression. However, a number of significant correlations and clustering were determined for rumen epimural microbiota and expression of sodium/hydrogen exchangers and claudin gene targets indicating the influence of epimural microbes on host gene expression is stronger than the effect of dietary change. Key Words: epimural microbes, gene expression, hay, pHThe importance of the studyThis work provides an understanding of the role of diet in altering gut microbiota to generate a host response. Furthermore, this study demonstrates that rumen microbial composition, and not rumen VFA composition, is the key factor driving host response. This provides a strong basis to consider individualized feeding programs based obtaining a desired gut microbiota.