The Effects of Different Concentrate-to-Forage Ratio Diets on Rumen Bacterial Microbiota and the Structures of Holstein Cows During the Feeding Cycle.

The objectives of this study were to investigate the ruminal bacterial changes during the feeding cycle. Six ruminally cannulated Holstein cows were used in this experiment. The high-forage (HF) and high-concentrate (HC) diets contained 70% and 30% dietary forage, respectively. Dairy cows were fed their respective diets for at least 28 days, then samples were collected at 0, 2, 4, 9, 12, 16 and 20 h post-feeding. The results showed that pH, the concentration of (total volatile fatty acids) TVFAs and the percentages of acetate, propionate and butyrate were significantly affected by diet and time interactions. The diversity of rumen microbiota in HF dietary treatments was significantly higher than that in the HC dietary treatments. ACE (Abundance-based Coverage Estimator) and Chao 1 indices peak at 12 h post-feeding and then decline over the next 8 h. The rumen microbiota was mainly composed of the phyla Firmicutes, Bacteroidetes and Proteobacteria without considering the diet and time. The Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) functional profile prediction indicated that the carbohydrate metabolism was different at 9, 12 and 20 h post-feeding time, which revealed that the soluble carbohydrates were enough for microbial fermentation shortly after feeding. This research gave a further explanation of the interactions among rumen microorganisms, which could further help manipulate the rumen metabolism.