Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 10, 1996
Publication Date: N/A
Interpretive Summary: Excess fat production in the modern broiler accounts for an annual loss to the poultry industry of 300 to 350 million dollars annually. The original source of this problem relates to selection genetic practices that emphasized rapid growth at the expense of other carcass characteristics. The literature is limited concerning the genetic x nutrition interaction involved in the control of fat synthesis in the modern broiler. We used a rapid growth strain of male chicks to study the effects of dietary protein on the ability of chicks to synthesize fat. The line is commercially used as source of female parent stock and does not result from selection pressures that entail an emphasis on fat synthesis. The line of chicks selected for rapid growth provided liver tissue that, when put into a culture system, exhibited a high rate of lipid synthetic ability. Plasma IGF-I may be a more sensitive indicator of changes in dietary protein than changes in intermediary metabolism. Selection criteria based on the feeding of high protein diets may result in broiler parent stock which sire leaner offspring.
Broiler chickens were fed diets containing either 12 or 21% protein from 7 to 28 d of age and then switched to the opposite level of protein for an additional 12 d. Birds were bled and killed at 0, 2, 5, 7, 9 and 12 d following the reversals. Measurements taken at these intervals included in vitro lipogenesis (IVL), growth and feed consumption, hepatic enzyme activities and plasma metabolites. Feeding these birds a higher protein diet from 28 to 40 d improved both growth and feed efficiency. Lipogenesis was also greater and insulin-like growth factor-I (IGF-I) less in birds fed the lower protein diet. Switching dietary treatments increased and decreased lipogenesis as birds were switched from high to low protein and low to high protein diets, respectively. Half-maximal changes were observed four days after the reversal and maximal changes seven days after the reversal. In contrast, switching dietary treatments decreased and increased plasma IGF-I, respectively, as birds were switched from high to low protein and low to high protein diets. Of the three hepatic enzymes monitored, malic enzyme activity most closely followed the rapid changes in IVL. Plasma IGF-I may be a more sensitive indicator of changes in dietary protein than changes in intermediary metabolism.