Gene expression of Red Angus sired steers and heifers evaluated for residual feed intake

To improve our mechanistic understanding of variation in residual feed intake (RFI), gene expression studies have been suggested. In the present study, 42 progeny (25 steers, 17 heifers) of Red Angus sires divergent for maintenance energy (ME) EPD were RFI–tested during an 84-d post-weaning period. Subsequently, biopsy samples were collected from the biceps femoris muscle and mRNA expression of key genes in various regulatory pathways was evaluated through quantitative real-time PCR. A 2-sample t-test at a 2-tailed P < 0.05 was used to identify differentially expressed genes in the 2 extreme RFI quartile groups. Fatty acid synthase (FASN) was expressed in greater abundance in inefficient (high RFI) compared with efficient (low RFI) animals (P = 0.03). Gene expression of C/EBPα (P = 0.06) and PPARγ (P = 0.13) also tended toward greater abundance in inefficient animals. When these data were analyzed by sex, inefficient heifers showed a similar expression pattern for C/EBPα (P = 0.003) and PPARγ (P = 0.08), while FASN tended to be up-regulated in inefficient steers (P = 0.11). These patterns of gene expression in skeletal muscle suggest that lipogenesis was up-regulated in inefficient heifers, while fatty acid synthesis was up–regulated in inefficient steers. In addition, IGFBP5 (P = 0.06) tended to be up-regulated in inefficient animals although there was no difference (P > 0.05) in expression of the type 1 IGF receptor, IGFBP2, IGFBP3 or growth hormone receptor (GHR). When analyzed by sex, inefficient heifers tended to show higher expression of IGFBP2 (P = 0.12), IGFBP3 (P = 0.15), IGFBP5 (P = 0.08), and GHR (P = 0.13), thus muscle anabolic processes may be altered. No differences in expression of these genes were detected in steers. Thus, differential gene expression provides a tool to suggest metabolic pathways that may be involved in RFI variation of beef cattle.