Residual feed intake in beef cattle and its association with carcass traits, ruminal solid-fraction bacteria, and epithelium gene expression

Background Residual feed intake(RFI) describes an animal’s feed efficiency independent of growth performance. The objective of this study was to determine differences in growth performance, carcass traits, major bacteria attached to ruminalsolids-fraction, and ruminalepithelium gene expression between the most-efficient and the least-efficient beef cattle. One-hundred and forty-nine Red Angus cattlewere allocated to three contemporary groups according to sex and herd origin. Animals were fed a finishing diet in confinement for 70 d to determine the RFI category for each. Within each group, the two most-efficient (n = 6; RFI coefficient = − 2.69 ± 0.58 kg dry matter intake (DMI)/d) and the two least-efficient animals (n = 6; RFI coefficient = 3.08 ± 0.55 kg DMI/d) were selected. Immediately after slaughter, ruminalsolids-fraction and ruminalepithelium were collected for bacteria relative abundance and epithelial gene expression analyses, respectively, using real-time PCR.