259 Late-Breaking: Residual feed intake in beef cattle is associated with differences in signaling mechanisms controlling protein synthesis in ruminal epithelium.

摘要

Residual feed intake (RFI) describes an animal’s feed efficiency independent of phenotypic performance. Because of their role in regulating global protein synthesis, an energy-costly process, differences in insulin and mTOR signaling in the ruminal epithelium between the most- and least-efficient animals might be part of the mechanisms associated with feed efficiency. One-hundred and forty-nine Red Angus cattle were allocated to three groups according to sex (heifers, steers) 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; RFI coefficient = -2.69 +/-0.58 kg dry matter/d) and least-efficient animals (n = 6; RFI coefficient = 3.08 +/- 0.55 kg dry matter /d) from each group were selected. At d 70, plasma samples were collected to determine insulin concentrations via ELISA, while ruminal epithelium was collected immediately after slaughter for protein abundance via western blot. No effect of sex was observed (P > 0.05) for plasma insulin and the 20 proteins evaluated in epithelium. Plasma insulin also did not differ (P = 0.73) between RFI groups. Among mTOR pathway-related proteins, the most-efficient group had lower abundance of a subset of total and phosphorylated (p) translation initiation and elongation proteins (EIF2α, P = 0.002; p-EIF2α, P = 0.004; EEF2, P = 0.04), the ribosome component RPS6 (P = 0.004), but abundance of the phosphorylated translation elongation factor p-EEF2 was greater (P = 0.02). Abundance of the insulin-responsive kinase AKT (P = 0.02) and insulin-sensitive transporter SLC2A4 was lower (P < 0.001) in the most-efficient group, and agrees with the greater p-EEF2 indicating overall lower protein synthesis. Data suggest that differences in signaling mechanisms controlling protein synthesis in ruminal epithelium are a component of feed efficiency in beef cattle.