Abstract
This study investigated whether dietary metabolizable energy (ME) could generate dynamical effects on rumen fermentation, gastrointestinal tract (GIT) morphology, and microbial composition of growing ewes. A total of twenty-eight female Hu lambs were randomly allotted to two treatments with different dietary ME levels: 9.17 (FEA) and 10.41 MJ/kg (FEB). These lambs were further made ready for a 67-day feeding trial. Results showed that the molar proportions of butyrate (p = .020), iso-valerate (p = .028), and valerate (p = .005) were significantly higher in the FEB group than those in the FEA group. The results of the GIT morphologic properties showed that the villus height (VH) (p = .005) was significantly higher and crypt depth was significantly deeper (CD) (p = .005) in the duodenum and that the rumen papillary height (PH) was significantly higher (p = .020) in FEB group compared with the FEA group. High-throughput sequencing results showed that 1826 operational taxonomic units (OTUs) were obtained and that the OTU number (p = .039), the ACE (p = .035), and Chao1 indices (p = .005) were lower in the FEB group. Moreover, 76 genera belonging to 21 phyla were detected in all samples; the relative abundance of Papillibacter (p = .036) and Flexilinea (p = .046) was significantly lower in the high energy group, whereas the relative abundance of unidentified Lachnospiraceae (p = .019), Acetitomaculum (p = .029), unidentified Veillonellaceae (p = .017), Anaerovibrio (p = .005), and Succinivibrio (p = .035) was significantly higher in the FEB group at the genus level. Furthermore, the relative abundance of genes and metabolic pathways were predicted by PICRUSt. The relative abundance of gene families related to carbohydrate metabolism was particularly higher (p = .027) in the FEB group. In summary, these results reveal that the dietary energy levels altered the composition and function of rumen microbiota and GIT morphology in growing female Hu sheep and provide a reference for optimizing diet formula and 10.41MJ/kg of ME level has been recommended in the growing period.