 This study investigated the correlation between host transcriptum, ruminarchia, and bacteria abundance, and residual feed intake, RFI, in three different beef cattle breeds, angus, charylase, and cancella. Differentially expressed genes and abundant ASVs were determined using INA sequencing and 16S RNA gene-amplicant sequencing. Significant correlations between gene expression and ASVs were found, with interesting associations observed for muscle contraction and immune system modulation. Potential functional candidate genes for feed efficiency status were identified for each breed. The results provide insights into the applicability of targeting host and rumin microbial traits for breeding more feed-efficient beef cattle. This article was authored by P.A.S. Fonseca, S. Lam, Y. Chen, and others.