Multi-omics analysis reveals circadian disruption of rumen microbiota and serum metabolites in Tibetan sheep under transport stress

BACKGROUND: Off-site fattening of Tibetan sheep is a key strategy to mitigate the effects of high-altitude grassland degradation and winter forage scarcity, promoting sustainable development in plateau animal husbandry. However, transport stress (TS) presents a significant challenge to realizing its benefits. The mechanism by which TS affects the health of Tibetan sheep by regulating rumen microbial and serum metabolite rhythmic changes remains unclear. METHODS: This study selected six healthy male Tibetan sheep, aged seven months and of comparable body weight, for the transport experiment. Blood and rumen fluid samples were collected at four-hour intervals during 24-hour periods pre-transport (CON) and post-transport (TS) for serum indicators, serum metabolome, and rumen microbiome analyses. RESULT: The results showed that TS significantly increased serum concentrations of cortisol (COR), melatonin (MT), lipopolysaccharide-binding protein (LBP), serum amyloid A (SAA), and non-esterified fatty acid (NEFA), while significantly decreasing glucose (GLU), total antioxidant capacity (T-AOC), and glutathione peroxidase (GPx) (P < 0.05). Furthermore, the circadian rhythms of COR, MT, LBP, SAA, NEFA, and GPx were significantly disrupted (ADJ.P < 0.05). TS reduced the proportion of rumen microbial circadian rhythms from 3.46% to 1.99%, with Prevotella, Butyrivibrio, and Ruminococcus losing their circadian rhythmicity in the TS phase (ADJ.P < 0.05). Additionally, TS decreased the proportion of circadian rhythm-regulated serum metabolites from 51.74% to 29.51%. In the TS phase, rhythmically regulated metabolites, including 3',5'-cyclic AMP, fumarate, dopamine, glutathione, and angiotensin (1-7), were enriched in pathways such as oxidative phosphorylation, retinol metabolism, and tryptophan metabolism. Multi-omics analyses demonstrated significant correlations between Ruminococcus and energy metabolites (malic acid, 3',5'-cyclic AMP, fumarate, NEFA), and between Butyrivibrio, Anaeroplasma, and inflammatory/antioxidant markers (glutathione, SAA, LBP). In conclusion, this study reveals that TS induces a homeostatic imbalance in Tibetan sheep by disrupting the circadian rhythms of both the rumen microbiota and host metabolism. These findings provide a theoretical basis and molecular targets for developing interventions to alleviate TS in livestock.