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 <i>Tan</i> sheep. This study employed an integrated multi-omics approach to compare rumen microbial communities (16S rRNA sequencing) and metabolomic profiles between <i>Tan</i> 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 (<i>p</i> > 0.05). However, the HADG group showed significantly higher final body weight (<i>p</i> < 0.05), markedly greater ADG and Average Daily Dry Matter Intake (ADFI) (<i>p</i> < 0.01), and a substantially lower FCR (<i>p</i> < 0.01). Plasma Total Antioxidant Capacity (T-AOC) and Superoxide Dismutase (SOD) levels were significantly elevated in the HADG group (<i>p</i> < 0.05), while Malondialdehyde (MDA) concentration was significantly reduced (<i>p</i> < 0.05). In contrast, plasma Globulin (GLB), Glucose (GLU), and Triglycerides (TG) concentrations were significantly lower in HADG sheep (<i>p</i> < 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 (<i>p</i> < 0.01), and significantly negatively correlated with 1-aminocyclopropanecarboxylic acid, pyridoxal phosphate, and 2-hydroxyglutarate (<i>p</i> < 0.05). Conversely, beta-alanine, ureidoacrylic acid, L-proline, and 2'-deoxyguanosine showed a highly significant positive correlation with norank_f__Bacteroidales_UCG-001 (<i>p</i> < 0.01), and a significant positive correlation with UCG-002 (<i>p</i> < 0.05). These findings elucidate the molecular mechanisms behind growth differences in <i>Tan</i> sheep and provide actionable insights for developing targeted nutritional strategies.