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

SIMPLE SUMMARY: The rumen is well-known as a natural bioreactor for the highly efficient degradation of fibers, and rumen microbes play an important role in fiber degradation. The rumen is a dynamic system that processes fibrous plant materials, and the rumen microbiota undergoes significant changes during the feeding cycle. However, there are few literatures about the feeding cycle effects on the microbial community. Therefore, we used high-throughput sequencing technology to monitor the ruminal bacterial changes during the feeding cycle. This study showed that there were regular changes in microorganisms and pH, and the relative content of the microorganisms recovered to their previous values prior to the next feeding. The microbial diversity of the forage group was higher than that of the concentrate group during the feeding cycle. At an earlier stage of feeding, the soluble carbohydrates are sufficient for microbial fermentation. Altogether, the results will help us to better understand the ruminal bacterial changes of dairy cows during the feeding cycle under high-forage/concentrate diets, which could provide further explanations of the interactions among rumen microorganisms and help manipulate the rumen metabolism. ABSTRACT: 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.