Residual Feed Intake in Beef Cattle and Hypothalamic Regulation of Appetite-Related Genes

Residual feed intake (RFI) describes an animal’s feed efficiency independent of phenotypic performance. The objective of this study was to determine expression differences of genes that regulate feeding behavior in the hypothalamus between the most-efficient and least-efficient animals, and any interaction with sex. One-hundred and forty-nine beef 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. Hypothalamic tissue was collected immediately after slaughter for gene expression analysis using real-time RT-PCR. Of the 32 genes evaluated, expression of POMC (P = 0.06) was upregulated in steers and MTOR (P = 0.13) tended to be upregulated in heifers. The most-efficient cattle tended to have greater GABBR1 expression (P < 0.15), while the least-efficient animals tended to have greater expression (P < 0.15) of CNR1, NPY2R and GCK. Results from RFI × sex interactions indicated that responses in gene expression of hypothalamus between steers and heifers were based on differences in RFI. PMCH was upregulated (P < 0.05) in most-efficient heifers but also (P < 0.05) in the least-efficient steers. Among the most efficient cattle, PMCH was upregulated (P = 0.01) in heifers compared with steers. In most-efficient steers, compared with heifers, there was upregulation of MC3R (P = 0.06) and a tendency for upregulation of FOXO1 (P = 0.12). In least-efficient heifers, compared with least-efficient steers, there was upregulation of AGRP (P = 0.05) by 2.1-fold. An RFI × sex also was observed where least-efficient heifers tended (P < 0.15) to have greater expression of FOXO1, CNR1 and MC3R by 1.2-, 2.0- and 2.3-fold, respectively. These findings indicate that differences in the hypothalamic gene expression that may play a role in feed efficiency in beef cattle could follow sex-dependent gene expression patterns.