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Dietary Crude Protein Changes Rapidly Alter Metabolism and Plasma Insulin-Like Growth Factor I Concentrations in Broiler Chickens^1,2,

Growth Biology Laboratory, Livestock and Poultry Science Institute, United States Department of Agriculture-Agricultural Research Service, Beltsville Agricultural Research Center, Beltsville, MD 20705

Although changes in dietary crude protein levels change metabolism in broiler chickens, there is little information concerning the time course of the process of adaptation. Therefore, male Indian River broiler chickens were fed diets containing either 120 or 210 g protein/kg from 7 to 28 d of age and then were fed the other level 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, growth and feed consumption, hepatic enzyme activities and plasma metabolites and metabolites. Birds fed the lower level of crude protein were smaller and less efficient in growth from 7 to 28 d. Feeding these birds a higher protein diet from 28 to 40 d improved both growth and feed efficiency. Lipogenesis was also greater and plasma 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 from low to high protein diets, respectively. Half-maximal changes were observed 4 d after the reversal and maximal changes 7 d after the reversal. In contrast, switching dietary treatments decreased and increased plasma IGF-I as birds were switched from high to low protein and from low to high protein diets, respectively. Half-maximal changes were observed 2 d after the reversal. Of the three hepatic enzymes monitored, malic enzyme activity most closely followed the rapid changes in in vitro lipogenesis. Plasma IGF-I may be a more sensitive indicator of changes in dietary protein than changes in intermediary metabolism.

KEY WORDS: • chickens • lipogenesis • diets • metabolism

¹ Mention of a trade name, proprietary product or specific equipment is not a guarantee or a warranty by the U.S. Department of Agriculture and does not imply and approval to the exclusion of other products.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed: GBL-LPSI, Room 212, Building 200, BARC-EAST, 10300 Baltimore Ave., Beltsville, MD 20705.

Manuscript received 29 March 1996. Revision accepted 29 July 1996.

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