Characterizing the dynamics of the rumen microbiota, its metabolites, and blood metabolites across reproductive stages in Small-tailed Han sheep.

Different reproductive stages of mammals involve complex biological processes, and the intestinal microbiota, as an endocrine organ or an "invisible organ," is involved in the regulation of hormone levels, immune function, and metabolism. However, the effects of the rumen microbiota, its metabolites, and blood metabolites on the reproductive performance of ruminants remain unclear. This study revealed that the Prevotella abundance increased significantly during pregnancy ( P < 0.01); the Fibrobacter abundance increased significantly during lactation ( P < 0.05); and rumen microbial carbohydrate metabolism, glucose biosynthesis, and metabolic functions were significantly enriched during pregnancy ( P < 0.05). Microbial metabolic profile analysis showed that the differentially abundant microbial metabolites during pregnancy and lactation were mainly enriched in the biosynthesis of ubiquinone and other terpenoid quinones, and there was a certain correlation with the microbiota. Among them, sapindoside A was increased during pregnancy, nicotinamide riboside and β-cryptoxanthin were reduced during pregnancy, and L-tryptophan was significantly increased during lactation. In addition, the volatile fatty acid levels in lactation were significantly higher than those in non-pregnancy and pregnancy ( P < 0.05), and the NH 3 -N content during pregnancy was significantly higher than that during lactation and non-pregnancy ( P < 0.05). Moreover, there were differences in the serum metabolite levels at different reproductive stages, and similar metabolites existed when comparing the rumen metabolites, which were mainly enriched in arachidonic acid metabolism, vitamin B6 metabolism, and ABC transporter protein, resulting in significantly higher serum IgA and IgM levels during lactation than during non-pregnancy and pregnancy ( P < 0.05).IMPORTANCEOur study illustrates the succession of the rumen microbiota and its metabolites in Small-tailed Han sheep at different reproductive stages. Among them, Firmicutes and Prevotella , which are related to energy metabolism, increased in abundance during pregnancy, while Fibrobacter , a fiber-degrading bacterium, increased in abundance during lactation. At the same time, the microbial metabolic profile and serum metabolic profile characteristics of different reproductive stages were revealed, and some functional pathways and metabolites related to energy and immunity were found. This study provides a reference for the health management of ruminants during non-pregnancy, pregnancy, and lactation.