Dietary energy alters jejunal microbial function without changing its structure in small-tailed Han sheep.

Dietary energy levels typically influence the structure and functional profile of the gastrointestinal microbial community. In this study, thirty 6-month-old Small-tailed Han (STH) sheep were randomly divided into three groups and fed corn-based diets with different energy levels for 150 days. Jejunal contents were then collected and analyzed using metagenomic sequencing to assess microbial alpha diversity and taxonomic composition. Functional annotation and enrichment analysis were performed using the KEGG database. Principal coordinate analysis (PCoA) and alpha diversity indices (Chao1, Shannon, Simpson and good coverage) revealed no significant changes in the overall structure or macro-ecological characteristics of the jejunal microbial community in response to dietary energy levels. At the phylum level, Bacillota was the absolutely dominant phylum, while at the genus level, Methanobrevibacter was the most abundant genus. The abundances of these core microbial taxa did not differ significantly among groups. However, KEGG functional enrichment analysis revealed significant differences in microbial functions between groups. The low-energy group exhibited enrichment in pathways related to energy deficiency and stress adaptation, whereas the high-energy group showed significant enrichment in pathways associated with active growth and anabolic metabolism. In conclusion, although dietary energy levels did not significantly alter the microbial community structure in the jejunum of STH sheep, they profoundly influenced its functional potential. These findings suggest that dietary energy may modulate host nutrient acquisition and health status by regulating the functional characteristics of the jejunal microbiota.