Rapid Dietary Protein Changes, Enzyme Activities, mRNAs and Plasma Hormones in the Broiler Chicken

Abstract

Ross 708 broiler chickens were fed one of three levels of crude protein (12, 21 or 30%) from 7 to 28 days of age. Birds were then switched to either a higher (30%) or lower level of crude protein (12% and sampled three days following the switch. The purpose of these treatments was to test effects of changes in protein level at a representative time during the finisher phase (days 28 to 31) of broiler growth and to relate changes to metabolic plasma hormone levels (IGF-I, IGF-II, insulin, leptin, T3, T4, glucagons, Ghrelin) and regulatory enzymes [malic enzyme (ME), aspartate aminotransferase (AAT), and NADP-isocitrate dehydrogenase (ICD)] and their respective mRNAs The data from this experiment show that a priority of hormones can be established with respect to correlations between circulating values and representative metabolic enzymes and their mRNAs. It is suggested from these data that both IGF-I and T4 are equal in a metabolic priority scheme and are superior to glucagon and Ghrelin which are still significantly related to certain enzymes and their mRNAs. It is entirely possible that mRNA levels do not correlate or totally regulate enzyme protein (as evidenced by activities of regulatory enzymes) although the relationships for ME (R = 0.69; P<0.001), ICD (R = 0.64; P <0.001) and AAT (R = 0.47, P<0.001) does lend some credence that transcriptional events regulate these two enzymes.