Effects of dietary non-fibrous carbohydrate (NFC) to neutral detergent fiber (NDF) ratio change on rumen bacterial community and ruminal fermentation parameters in Chinese black Tibetan sheep (Ovis aries)

This study evaluated the effects of different non-fibrous carbohydrate/neutral detergent fiber (NFC/NDF) ratios on the rumen fermentation parameters and bacterial community of black Tibetan sheep. Fifteen 2-month-old rams with an average body weight of 10.45 +/- 0.96 kg were randomly assigned to three treatments and fed NFC/NDF of 1.82 (H group), 1.16 (M group), and 0.71 (L group), respectively. This study was conducted for 127 d, including 7 d of adaption to the diets. The fermentation parameters and bacterial characteristics of rumen fluid were measured after the end of feeding trials. According to the results, the concentrations of propionate and total volatile fatty acids (TVFA) increased in the H group than those in the L group (P < 0.05), while the concentration of acetate was highly increased in the L group (P < 0.05). A total of 1463 OTUs were obtained with 97% consistency. Both phylum Bacteroidetes and Firmicutes were dominant bacterial phyla. Proteobacteria accounted for a significantly higher proportion of bacteria in the L group than in the H and M groups (P < 0.05). At the genus level, the main cellulose-degrading bacteria, such as Prevotella_1, Prevotellaceae UCG-003 and Ruminococcus_1 possessed a higher relative abundance in dietary NFC/NDF ratio of 0.71 (P < 0.05). Correlation analysis revealed that the abundance of Patesicbacteria was negatively associated with TVFA, whereas the abundance of Bacteroidetes was positively associated with TVFA. Using clusters of orthologous groups (COG), the functions of the rumen microbial community were mainly enrichment in amino acid metabolism and carbohydrate metabolism. In summary, ruminal bacterial community composition and fermentation characteristics were altered under different dietary NFC/NDF ratios in black Tibetan sheep.