This study investigated the effects of the dietary protein level and rumen-protected methionine and lysine (RPML) on the growth performance, rumen fermentation, and serum indexes of yaks. Thirty-six male yaks were randomly assigned to a two by three factorial experiment with two protein levels, 15.05% and 16.51%, and three RPML levels: 0% RPML; 0.05% RPMet and 0.15% RPLys; and 0.1% RPMet and 0.3% RPLys. The trial lasted for sixty days. The results showed that the low-protein diet increased the DMI and feed conversion ratio of yaks. The diet supplemented with RPML increased the activities of IGF1 and INS and nutrient digestibility. The high-protein diet decreased the rumen butyrate concentration and increased the rumen isovalerate concentration. The low-protein diet supplemented with RPML increased the rumen pH and the concentrations of total volatile fatty acids, butyrate and NH₃-N; the high-protein diet supplemented with a high level of RPML decreased the rumen pH and the concentrations of isobutyrate, isovalerate, propionate and NH₃-N. The low-protein diet supplemented with RPML increased the total antioxidant capacity and glutathione peroxidase activity, along with the concentrations of malondialdehyde and amino acids such as aspartic acid, lysine, cysteine, etc. In conclusion, a low-protein diet supplemented with RPML is beneficial for rumen and body health, physiological response, and metabolic status in yaks.

Yak (Bos grunniens) meat is popular with a unique flavor and high nutritional value. This study investigated the effects of dietary supplementation with rumen-protected methionine (RPM) on meat quality, fatty acid composition, volatile flavor compounds, and transcriptomics of Longissimus lumborum of yak. Twenty-four male Maiwa yaks were selected and assigned to four groups: basal diet (CON), or supplementation of 5 g/d (RPM5), 10 g/d (RPM10), and 15 g/d (RPM15) RPM. The dose-dependent effects of RPM levels were evaluated through linear or quadratic trend analysis. The results showed that diet supplementation with RPM increased the intramuscular fat contents, improved composition of volatile flavor compounds and the ratio of monounsaturated fatty acids to saturated fatty acids. Compared to the CON group, there were 36, 84 and 23 up-regulated genes, and 85, 94 and 70 down-regulated genes in the RPM5, RPM10 and RPM15 groups, respectively. Gene ontology enrichment analysis revealed significant differentially expressed genes enrichment in biological processes, cellular components, and molecular functions across RPM5, RPM10, and RPM15 groups compared to the CON. KEGG pathway analysis revealed 99, 169, and 104 enriched pathways in RPM5, RPM10, and RPM15 groups, respectively. In summary, the addition of RPM to diets may provide new ideas and methods to improve meat quality of yaks.

This study employed integrated transcriptomics and proteomics analysis to investigate the potential role of methionine (Met) in regulating the proliferation, differentiation, and lipid deposition of yak intramuscular preadipocytes (YIMA). Five Met concentrations (0, 0.05, 0.5, 5, and 50 mM) were used to establish the Met model of YIMA. The results of Bodipy, Oil Red O, EdU staining, and qPCR showed that the appropriate Met (0.05, 0.5, and 5 mM) supplementation significantly promoted the proliferation and adipogenic differentiation of YIMA, whereas excessive Met (50 mM) markedly inhibited these processes. To further evaluate the mechanism of Met on YIMA, cells supplemented with 0 mM (control, CON), 0.5 mM (moderate) and 50 mM (excessive) Met were selected for the transcriptomic and proteomic analyses. The results showed that moderate Met treatment primarily enriched pathways related to extracellular matrix–receptor interaction and the PI3K/AKT signaling pathway, while excessive Met significantly enriched processes involving abnormal methylation, DNA damage, and metabolic stress. Functional validation experiments further confirmed that Met regulates YIMA proliferation and differentiation by upregulating p-Akt protein expression and activating the PI3K/AKT pathway. These findings provide molecular insights that support improving yak meat quality and IMF content through dietary Met supplementation.