Diet dominates age in shaping the rumen bacteria community and function in dairy cattle

Abstract Background To understand the effects of diet and age on the rumen bacterial community and function, forty-eight dairy cattle at 1.5 (M1.5), 6 (M6), 9 (M9), 18 (M18), 23 (M23), and 27 (M27) months old were selected. The M1.5, M6, and M27 had the high protein and starch dietary, while the M9, M18, and M23 had the high fiber dietary. Fermentation profile, enzyme activity, and bacteria community in rumen fluid were measured. Results The acetate to propionate ratio (A/P) at M9, M18, and M23 (high fiber diet) was higher than other ages, and M6 was the lowest (P < 0.05). The total volatile fatty acid (TVFA) at M23 and M27 was higher than other ages (P < 0.05). The urease at M18 was lower than M1.5, M6, and M9, and the xylanase at M18 was higher than M1.5, M23, and M27 (P < 0.05). The α-diversity indexes (Ace and Chao1) of ruminal bacteria increased from M1.5 to M23, while they decreased from M23 to M27 (P  4. The variation partitioning approach analysis showed that the age and diet had a 7.98% and 32.49% contribution to the rumen bacteria community variation, respectively. The richness of Succinivibrionaceae_UCG-002 and Fibrobacter were positive correlated with age (r > 0.60, P  0.50, P < 0.01). The Lachnospiraceae_AC2044_group, Pseudobutyrivibrio, and Saccharofermentans has a positive correlation (r > 0.80, P < 0.05) with diet NDF and negative correlation (r < -0.80, P  0.50, P < 0.01). Conclusion These findings indicated that the quantitative effect of diet and age on the rumen bacteria were 7.98% and 32.49%, respectively. The genera of Lachnospiraceae_AC2044_group, Pseudobutyrivibrio, and Saccharofermentans could be worked as the target bacteria to modulate the rumen fermentation by diet; meanwhile, the high age-correlated bacteria such as Succinivibrionaceae_UCG-002 and Fibrobacter also should be considered when shaping the rumen function.