Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 16, 2001
Publication Date: June 1, 2002
Citation: Comparative Biochemistry & Physiology 132:423-431, 2002.
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 yshunted 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 ver high level of protein. Modest increases in dietary protein will decrease lipid synthesis without affecting gene expression.
The purpose of this experiment was to determine the possible relationship 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, 21 or 30% protein ad libitum. In addition, another group of birds was feed on a regimen consisting of a daily change in the dietary protein level (12 or 30%). This latter group was further subdivided such that one-half of the birds received each level of protein on alternating days. Birds were sampled from 28 to 30 days of age. Measurements taken included in vitro lipogenesis, hepatic enzyme activities and gene expression of these enzymes and thyroid hormone levels. 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%. In contrast, expression of malic enzyme, fatty acid dsynthase and acetyl CoA carboxylase genes were constant over a dietary protein range of 12 to 21%, but decreased by feeding a 30% protein diet (acute or chronic feeding). Increasing dietary protein increased the activities of both aspartate aminotransferase and isocitrate dehyrogenase. Results of the present study demonstrate a continued role for protein in the regulation of broiler metabolism. It should be pointed out, however, that metabolic regulation at the gene level only occurs when feeding very high levels of dietary protein.