Effects of different proportions of ground corn and steam-flaked corn diets on growth performance, serum biochemical parameters, rumen fermentation and rumen microbial metagenome of yaks

This study objected to assess the effect of substituting ground corn (GC) with steam-flaked corn (SFC) at various ratios on growth performance, serum biochemistry, rumen fermentation, and microbiome in fattening yaks. Fifty male Maiwa yaks (196.43 +- 16.08 kg) were randomly assigned to five groups: SFC 0, SFC 25, SFC 50, SFC 75, and SFC 100, representing 0%, 25%, 50%, 75%, and 100% substitution of GC with SFC. Results showed that the dry-matter intake (DMI) in SFC 0 group was significantly lower than those in other treatment groups (P < 0.05). Among the serum biochemical parameters, the triglyceride (TG) content in the SFC 100 group was significantly higher than other treatment groups (P < 0.05), with a quadratically increase (P < 0.05). Regarding rumen fermentation parameters, the propionate in the SFC 50 and SFC 100 groups was significantly higher than in the other groups (P < 0.05). At the phylum level of the rumen microbiome, the replacing with SFC significantly increased the relative abundance of Planctomycetota, Bacteria, and Candidatus_Saccharibacteria (P < 0.05). At the genus level, the replacing with SFC significantly increased the relative abundance of Paludibacteraceae and Bacteria (P < 0.05). Among the CAZy enzymes in the rumen, the relative abundance of cellulase modules (CM) in the SFC 0 group was significantly higher than other groups (P < 0.05). In conclusion, replacing 50% of GC with SFC may be an effective strategy to enhances growth performance in yak farming by improving rumen fermentation, microbiome composition, and carbohydrate-active enzymes.