Protein levels alter yak rumen microbiota profiles, meat properties, and longissimus dorsi metabolites.

Objective: The study investigated how varying protein levels in low-energy diets affected the microbiota, meat quality, and metabolomics of the imus dorsi muscle in yaks. The aim was to determine the optimal yak diet for growth and meat quality under low-energy conditions.

Methods: Twenty-four adult male yaks were divided into two groups of 12: the Low-energy, Medium-protein (LM) group and the Low-energy, High-protein (LH) group.The study analysed rumen microbiota and longissimus dorsi muscle metabolites using 16S rDNA gene sequencing and untargeted metabolomic analysis. The effects of the diets on growth performance, meat quality and microbial community composition were evaluated.

Results: There were no significant differences in growth performance between the LH and LM groups. However, the LH group had a lower pH value at 45 minutes after death and was better for meat colour and tenderness.There were no significant differences in average daily gain, cooking loss, hardness, elasticity, adhesiveness, chewiness, or the pH at 24 hours after death in the longissimus dorsi muscle between the groups. Microbial community analysis revealed no significant differences in diversity indices; however, it did indicate distinct bacterial composition between the groups. Predictions of function suggested the LM group had a higher level of enrichment and a greater number of unique OTUs compared to the LH group.Metabolomic analysis revealed differences in muscle metabolites and metabolic pathways, with the LM group having a higher capacity for fatty acid and selenocompound metabolism, implying greater energy utilisation efficiency and antioxidant function.

Conclusion: The study suggests that a diet with 14% protein, as part of low-energy diets, is best for increasing yak fattening. This is because it improves energy use and antioxidant function, without affecting growth.