Multi-Omics Analysis Reveals Concentrate Supplementation Alleviates Body Weight Loss by Regulating Rumen Function in Lactating Tibetan Sheep During the Cold Season

The parturition season of grazing Tibetan ewes spans from October to March, a period that exacerbates the adverse impacts of nutrient-deficient herbage on milk yield, body condition, and postpartum recovery. To alleviate the weight loss of ewes during the cold seasons, we provided concentrate supplements at four levels (dry matter (DM) basis), 260 g (C1), 440 g (C2), 520 g (C3), and 610 g (C4), alongside a basal diet of grazed pasture. A total of 96 multiparous Tibetan ewes (third parity, body weight: 45.17 ± 3.69 kg (body weight (BW) were enrolled within 12-18 h postpartum and randomly allocated to four dietary groups (<i>n</i> = 24 ewes per group). We measured growth performance, ruminal histomorphology, fermentation parameters, and digestive enzymes. A multi-omics technique (16S rRNA gene sequencing and RNA-seq) was employed to investigate the mechanisms underlying alterations in ruminal function. The results showed that increasing the concentrate level decreased body weight loss and increased average dry matter intake (<i>p</i> < 0.05). Rumen morphology was significantly altered: papilla width and muscle layer thickness were greatest in the C4 group, whereas submucosal thickness was highest in the C1 group (<i>p</i> < 0.05). Cellulase activity was lowest in the C1 group (<i>p</i> < 0.05). Papilla width of lactating Tibetan ewes in the C4 group was higher (<i>p</i> < 0.05) than that in the C1 and C3 groups. Concentrate supplementation altered ruminal microbiota composition and diversity. Each group exhibited a distinct microbial signature: the C1 group was characterized by <i>Lachnospiraceae_XPB1014_group</i>, <i>Candidatus_Omnitrophus</i>, <i>Paenibacillus</i>, and <i>unclassified_Oligoflexaceae</i>; the C2 group was enriched in <i>Papillibacter</i>, <i>Anaerovibrio</i>, <i>V9D2013_group</i>, and <i>unclassified_Peptococcaceae</i>; the C3 group was characterized by <i>unclassified_Bacteroidales_RF16_group</i>; and the C4 group was characterized by <i>Ruminococcus</i>, <i>Pseudobutyrivibrio</i>, and <i>Mitsuokella</i> (<i>p</i> < 0.05). Transcriptomic analysis identified differentially expressed genes (<i>TRPA1</i>, <i>EPHB1</i>, <i>GATA3</i>, <i>C4</i>, <i>ABCG2</i>, <i>THBS4</i>, and <i>TNFRSF11B</i>) that are predominantly involved in immune regulation, signal transduction, and nutrient digestion. The results of Spearman correlation analysis showed that <i>Anaerovibrio</i> was negatively correlated with propionate (r = -0.565, <i>p</i> < 0.05). However, it was positively correlated with the ratio of acetate and propionate (r = 0.579, <i>p</i> < 0.05). Moreover, <i>Lachnospiraceae_XPB1014_group</i> was negatively correlated with cellulase (r = -0.699, <i>p</i> < 0.05) and α-amylase (r = -0.514, <i>p</i> < 0.05). These findings suggest that the increasing concentrate supplementation alleviates body weight loss in lactating Tibetan sheep by orchestrating improvements in rumen histomorphology, digestive function, altering bacteria composition, and ruminal immune and modulating host epithelial gene expression.