Metagenomics Analyses of Cellulose and Volatile Fatty Acids Metabolism by Microorganisms in the Cow Rumen

The purpose of this study was to evaluate the effects of different forage-to-concentrate (F:C) ratios (7:3 high-forage, 3:7 high-concentrate) on rumen microflora and fiber degradation mechanism. Compared with the high-concentrate (HC) group, the high-forage(HF) group showed improved fiber degradation and a sustained high level of carboxymethyl cellulose (CMCase), {beta}-glucosidase and {beta}-xylosidase activities, but the total VFAs decreased. Among bacteria at the family level, Lachnospiraceae and Succinivibrionaceae in HF groups were 2-fold and 4-fold more abundant than in the HC group, respectively. A KEGG analysis revealed that succinate-CoA synthetase (EC: 6.2.1.5) and propionate-CoA transferase (EC: 2.8.3.1) leading directly to propionate production were more abundant in HC group. Conversely, butyryl-CoA dehydrogenase (EC: 1.3.8.1) was directly related to butyrate production and was higher in the HF group. A gene expression analysis showed that the relative content of Fibrobacter succinogenes and Butyrivibrio fibrisolvens was higher in the HF group and contributed more to fiber degradation and VFA production. Prevotella ruminicola, Selenomonas ruminantium, and Veillonella alkalescens contributed more to starch degradation and propionate production, which relative content was higher in the HC group. This research gave a further explanation of the fiber degradation parameters and microbiota under different F:C ration. The fiber-degrading bacteria in the roughage group have a high content level, and the corresponding cellulase activity is also high. These results supported the potential of diets for microbial manipulation, which can increase feed digestibility and explored new fibrinolytic bacteria.\n\nIMPORTANCEThe forage of the cows feed occupies a large proportion. The shortage of high-quality forage in cow breeding has become an important factor limiting the Chinas dairy industry. The effective measure is to improve the utilization of low-quality forage. Based on traditional nutrient metabolism, the reasons for the effects of roughage on the growth and metabolism of dairy cows can be explored, but the metabolic mechanism is not well analyzed, and the further utilization of forage is also limited. Metagenomics has proven to be a powerful tool for studying rumen microbial structures and gene function. This experiment used metagenomics to study the metabolism of cellulose and volatile acids in the rumen. Our research showed that different forage-to-concentrate shifted the composition of microorganisms and the activity of enzymes, resulting in different metabolic pathways of volatile fatty acids. This work provides a background for microbial community composition and further use of forage.