Submitted to: Growth Development and Aging
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 2, 2009
Publication Date: January 11, 2010
Citation: Rosebrough, R.W., Richards, M.P., Mcmurtry, J.P., 2010. Rapid dietary protein changes and relationships among enzyme activities, their RNA's and plasma hormone levels in the broiler chicken. Avian Biology Research. 3(1):7-16.
Interpretive Summary: Excess fat production by the modern broiler chicken presents a two-fold problem. The consumer has health concerns about the link between cardiovascular disease and dietary fat. The producer would like to produce more lean meat rather than fat condemned at the processing plant. Historically shifts in metabolism have resulted in dietary fat being merely shunted to replace that synthesized from other feed ingredients. We have found that altering feeding regimens and dietary crude protein in the broiler will cause permanent changes in fat synthesis and storage, such that dietary fat will not be shunted to body fat stores. The present study was designed to determine if dietary protein elicited changes in intermediary metabolism and if changes resulted from alterations in the expression of genes coding for certain regulatory proteins. Although increasing dietary protein decreased fat synthesis by the broiler, gene expression did not accompany this decrease unless the diet contained a very high level of protein. Modest increases in dietary protein will decrease lipid synthesis without affecting gene expression.
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 higher (12 to 30%, 21 to 30%) or lower levels of crude protein (30-12%, 21-12%) 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 hormone levels and regulatory enzymes [malic enzyme, ME; aspartate aminotransferase, AAT; isocitrate dehydrogenase (NADP), ICD activities and mRNA]. The data from this experiment also show that a priority of hormones can be established as far as correlations between circulating values and representative metabolic enzymes and their mRNA's. 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 mRNA's. It is entirely possible that mRNA levels will not correlate or totally regulate enzyme protein (as evidenced by activities of ME, ICD and AAT activities) although the relationships for ME (R = 0.69; P<0.01) and ICD (R=0.64; P<0.01) does lend some credence that transcriptional events regulate these two enzymes.