Grain Feeding Improves Yak Meat Tenderness and Lipid Deposition: Meat Quality, Amino Acid and Fatty Acid Profiles, Metabolomics, and Transcriptomics

Grain feeding is used to alleviate grazing pressure on the Tibetan Plateau. This study employed metabolomics and transcriptomics to elucidate the regulatory mechanisms of grain feeding on yak (Bos grunniens) meat quality, intramuscular fat, and amino acids. The results demonstrate that grain feeding significantly reduces meat shear force (11.05 vs. 18.98) and increases intramuscular fat content (1.48 g/100 g vs. 0.75 g/100 g). This is accompanied by elevated levels of monounsaturated and saturated fatty acids, alongside a decreased proportion of n-3 PUFAs, leading to a higher n-6/n-3 ratio of 5.13. Mechanistically, metabolomic analysis identified 83 differential metabolites, including flavor-related nucleosides, amino acids, and key lipids, such as palmitoleic and oleic acid, which collectively contribute to improved flavor and tenderness. Concurrently, transcriptomics revealed 1047 differentially expressed genes enriched in lipid metabolism pathways, including PPAR signaling, steroid biosynthesis, and glycerolipid metabolism. The PPAR signaling pathway plays a central role in coordinating lipid synthesis, and critical genes, such as PNPLA2, PPARA, SREBF1, and PRKAA1, were highlighted. In conclusion, grain feeding improves yak meat tenderness and fat deposition by modulating lipid metabolism at both the transcriptional and metabolic levels. This improvement, however, is balanced against a less favorable n-6/n-3 PUFA ratio.