Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 22, 2008
Publication Date: May 1, 2008
Citation: Rosebrough, R.W., Russell, B.A., Richards, M.P. 2008. Short term changes in the expression of lipogenic genes in broilers. Comparative Biochemistry and Physiology, Part A 149:389-395. 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.
Technical Abstract: The purpose of these experiments were to determine possible relationships between certain indices of lipid metabolism and specific gene expression in chickens fed graded levels of dietary crude protein. Male, broiler chickens growing from 7 to 28 days of age were fed diets containing 12 or 30% protein ad libitum. Both groups were then switched to opposite levels of protein. Birds were killed on day 28 (basal values prior to the switch) and at 12, 18 and 24 hr post switch. Measurements taken included in vitro lipogenesis, malic enzyme activity the expression of the genes for malic enzyme, fatty acid synthase and acetyl coenzyme carboxylase. In vitro lipogenesis and malic enzyme activity were inversely related to dietary protein levels (12 to 30%) and to acute changes from 12 to 30%. Malic enzyme, fatty acid synthase and acetyl CoA carboxylase genes were constant over a dietary protein range of 12 to 21% as in previous experiments, but decreased by feeding a 30% protein diet in the present experiments (acute or chronic feeding). Results of the present study demonstrate a continued role for protein in the regulation of broiler metabolism. Metabolic regulation at the gene level only occurs when feeding very high levels of dietary protein.