Integrative Multi-Omics Analysis of the Rumen in Tan Sheep with Contrasting Average Daily Gain

Understanding the drivers of average daily gain (ADG) is key to enhancing the productivity of Tan sheep. This study employed an integrated multi-omics approach to compare rumen microbial communities (16S rRNA sequencing) and metabolomic profiles between Tan sheep with high (HADG) and low (LADG) ADG. The novelty of this work lies in the systems-level identification of functional linkages between specific rumen bacteria and metabolites that underlie divergent growth phenotypes. The results revealed no significant difference in initial body weight between the two groups (p > 0.05). However, the HADG group showed significantly higher final body weight (p < 0.05), markedly greater ADG and Average Daily Dry Matter Intake (ADFI) (p < 0.01), and a substantially lower FCR (p < 0.01). Plasma Total Antioxidant Capacity (T-AOC) and Superoxide Dismutase (SOD) levels were significantly elevated in the HADG group (p < 0.05), while Malondialdehyde (MDA) concentration was significantly reduced (p < 0.05). In contrast, plasma Globulin (GLB), Glucose (GLU), and Triglycerides (TG) concentrations were significantly lower in HADG sheep (p < 0.05). Rumen metabolomics identified 265 differentially abundant metabolites between groups, with 64 down-regulated and 201 up-regulated in LADG compared to HADG sheep. These metabolites were significantly enriched in tyrosine metabolism, β-alanine metabolism, and thiamine metabolism pathways. Receiver Operating Characteristic (ROC) curve analysis identified 15 key differential metabolites, including succinic acid, 2-hydroxyglutarate, and pyridoxal phosphate. 16S rRNA sequencing indicated significant differences in microbial genera such as UCG-002, Blautia, norank_f__Bacteroidales_UCG-001, and norank_f__norank_o__Rhodospirillales. Correlation analysis revealed that UCG-002 and norank_f__Bacteroidales_UCG-001 were highly negatively correlated with succinic acid (p < 0.01), and significantly negatively correlated with 1-aminocyclopropanecarboxylic acid, pyridoxal phosphate, and 2-hydroxyglutarate (p < 0.05). Conversely, beta-alanine, ureidoacrylic acid, L-proline, and 2'-deoxyguanosine showed a highly significant positive correlation with norank_f__Bacteroidales_UCG-001 (p < 0.01), and a significant positive correlation with UCG-002 (p < 0.05). These findings elucidate the molecular mechanisms behind growth differences in Tan sheep and provide actionable insights for developing targeted nutritional strategies.