An integrative multi-omics investigation into the influence of forage type on the volatile flavor profile of Ujumqin sheep mutton

China ranks among the leading producers and consumers of mutton globally and the development of nutritional strategies to improve meat quality and sensory attributes. This study investigated the effect of three high-quality forages, i.e., alfalfa hay (ALFA), Leymus chinensis hay (LEYM) and oat hay (OATS) compared to corn stalks-based control diet (CORN) on rumen microbiota, metabolomics profiles, and muscle volatile flavor compounds in lambs through a multi-omics integration approach. Forty male lambs were randomly allocated into four dietary groups (n = 10/group) and fed a concentrated forage supplement for 91 days. From each group, six lambs (n = 6/group; totla 24) were slaughtered. Rumen fluid and longissimus dorsi muscle samples were collected for metagenomics, untargeted metabolomics, and volatile flavor analysis. Differential microbial taxa were identified using LEfSe analysis, followed by integrated Pearson correlation and MetoOrigin analysis to link microbiota, metabolites, and metabolic pathways. Associations with muscle volatile flavor compounds were also assessed. LEfSe analysis identified 4, 3, and 7 differentially abundant rumen microbial taxa in the ALFA, LEYM and OATS groups, respectively, compared to CORN. Integrated analysis showed these taxa correlated with 4, 9 and 11 rumen metabolites via 3, 11 and 7 microbial or host-microbial co-metabolic routes, respectively. These metabolic changes were strongly associated to alterations in muscle volatile flavor compounds. Particularly, the ALFA diet increased volatile compounds associated with fresh, grassy, floral, and citrus-like odors reduced mutton-related Pyrazine (2,5-dimethyl-). The LEYM diet reduced Pentaborane(9) and Pyrazine, which are associated with undesirable mutton like odors. The OATS diet increased 2-Nonanone and Phenylethyl Alcohol (fruity and floral smells), while suppressing n-Decanoic acid and n-Octanoic acid (associated with characteristic mutton aroma). These results showed that high-quality forages improve the mutton flavor by regulating the rumen micro-ecological network and associated metabolic pathways along the forage-microbiota-metabolites-muscle flavor axis. These findings provide a theoretical foundation for precise nutritional interventions aimed at enhancing meat quality in lambs.