Residual Feed Intake in Beef Cattle and Its Association with Ruminal Epithelium Gene Expression

Residual feed intake (RFI) describes an animal’s feed efficiency independent of phenotypic performance. The objective of this study was to determine differences in gene expression of ruminal epithelium between the most-efficient and the least-efficient animals, and any interaction with sex. One-hundred and forty-nine Red Angus cattle were allocated to three groups according to sex and herd origin. Animals were fed a finishing diet in confinement for 78 d to determine the RFI category for each. Within each contemporary group, the two most-efficient (n = 6) and least-efficient animals (n = 6) were selected. Ruminal epithelium was collected immediately after slaughter for gene expression analysis using real-time RT-PCR. Data were analyzed using the MIXED procedure of SAS 9.3. Fixed effects in the model included RFI category, sex and RFI × sex. Individual animal was the experimental unit and incorporated into the statistical model as a random effect nested within group. Of the 48 genes evaluated, compared with steers, heifers had a higher expression of FFAR2 (P < 0.01). The most-efficient cattle had a decrease in ACADS (P < 0.01) and HMGCS2 (P = 0.05), both of which are involved in ketogenesis. Efficient animals also had lower expression of SLC16A (P = 0.06), a monocarboxylate VFA transporter. Results from RFI × sex interactions indicated that responses in gene expression between steers and heifers were based on differences in RFI. For example, compared with heifers, steers at the high-efficiency level had greater expression of HIF1A, SLC25A20 and COX8A (P < 0.05), involved in VFA absorption and energy generation through oxidative phosphorylation, while heifers had greater expression for the VFA transporter SLC9A1 (P = 0.04) compared with steers at the lower feed efficiency level. An RFI × sex effect also was observed where most-efficient steers had greater expression of HIF1A, SLC9A1 and COX8A (P < 0.05) compared with least-efficient steers. In heifers, however, SLC9A1 and COX8A had greater expression in least-efficient heifers (P < 0.05) compared with the most-efficient heifers. These findings indicate that differences in the ruminal epithelium gene expression that may play a role in feed efficiency in beef cattle could follow sex-dependent gene expression patterns.