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An Examination of the Role of Feeding Regimens in Regulating Metabolism During the Broiler Breeder Grower Period. 1. Hepatic Lipid Metabolism

M. de Beer^*, R. W. Rosebrough, B. A. Russell, S. M. Poch, M. P. Richards and C. N. Coon^*,1

^* Center of Excellence for Poultry Science, University of Arkansas, Fayetteville 72701; and Growth Biology Laboratory, USDA-Agricultural Research Service, Beltsville, MD 20705

¹ Corresponding author: ccoon{at}uark.edu

A trial was conducted to determine the effects of feeding regimens on hepatic lipid metabolism in 16-wk-old broiler breeder pullets. A flock of 350 Cobb 500 breeder pullets was divided into 2 at 4 wk of age and fed either every day (ED) or skip-a-day (SKIP) from 4 to 16 wk of age. Total feed intake did not differ between the 2 groups. At 112 d, 52 randomly selected ED-fed pullets, and 76 SKIP-fed pullets were individually caged and fed a 74-g (ED) or 148-g (SKIP) meal. Four pullets from each group were killed at intervals after feeding and livers were collected, weighed, and snap-frozen for determination of lipogenic gene expression. Total RNA was isolated from livers using Trizol reagent and then quantitatively measured by noting the optical density 260:280 ratio and qualitatively measured by gel electrophoresis. The expression of certain regulatory genes in metabolism [acetyl coenzyme A carboxylase; fatty acid synthase; malic enzyme (MAE); isocitrate dehydrogenase (ICDH); and aspartate aminotransferase (AAT)] were determined by real-time reverse-transcription PCR. Remaining liver portions were analyzed for enzyme activity of MAE, ICDH, and AAT as well as glycogen and lipid contents. Liver weight was higher in SKIP than in ED birds. Feeding caused dramatic increases in liver weight, glycogen, and lipids of SKIP birds. Expression of acetyl coenzyme A carboxylase, FAS, and MAE genes were increased in SKIP birds 12 and 24 h after feeding, with the increases in MAE expression from 0 to 24 h after feeding being of the greatest magnitude. In contrast, SKIP decreased ICDH and AAT gene expression, which parallels findings noted in fasting-refeeding experiments conducted with much younger birds. Skip-a-day feeding resulted in far greater changes in gene expression compared with ED, which was indicative of the inconsistent supply of nutrients in such regimens. Enzyme activity of MAE, ICDH, and AAT was reflective of noted changes in gene expression. In summary, the feeding regimen greatly affected hepatic gene expression in breeder pullets.

Key Words: breeder • feeding regimen • lipogenic gene expression