Abstract: This experiment aimed to explore the effects of dietary energy level on rumen fermentation characteristics and microbial composition of Hu Sheep. Forty-eight Hu sheep (body weight (17.77±1.15) kg) were randomly divided into two groups:1) Control group (C group), metabolizable energy (ME)=8.83 MJ·kg^-1; 2) High energy group (H group), ME=10.84 MJ·kg^-1, with 6 replicates per group and 4 sheep in each replicate. The experiment lasted for 105 days, including 15 days of pre-experiment and 90 days of formal experiment. At the end of experiment, rumen fluid was collected to determine rumen fermentation characteristics, and 16S rRNA high-throughput sequencing was performed on V3-V4 region of microbial bacteria to detect rumen microbial composition. Results were showed as follows:1) There were no significant differences in rumen pH, total volatile fatty acids, acetate, propionate, isobutyrate, butyrate, isovalerate, valerate, acetate to propionate ratio, ammonia nitrogen, and microbial crude protein concentrations between H and C groups (P>0.05); 2) Alpha diversity showed that Chao 1, Observed species, PD whole tree, and Shannon index were lower in H group than those in C group (P<0.05); 3) Taxonomic annotations showed that Bacteroidetes and Firmicutes accounted for the highest proportion, whereas no significant differences were observed between H and C groups regarding these two phyla (P>0.05). The relative abundances of Ruminococcus and Anaerovibrio were higher in H group than those in C group (P<0.05). These results indicate that under the condition of the current experiment, the increased dietary energy level did not alter rumen fermentation characteristics significantly, but reduced the richness and evenness of rumen bacteria, as well as variations in relative abundances of some bacteria.

Key words: Hu sheep, energy level, rumen fermentation characteristics, rumen microbial composition