Energy and protein relations in the broiler chicken. 2. Effect of varied protein and constant carbohydrate levels on body composition and lipid metabolism.

Male broiler chicks were fed diets containing 18, 23 or 30% protein on an ad libitum basis for 3 weeks. Chicks were also fed these diets on a restriction regime consisting of seven 3-day cycles (2 days with and 1 day without feed). Another group of chicks were fed diets containing 12, 23 or 30% protein on a 3-day rotation consisting of a daily change in dietary protein. Ad libitum. Feed intakes of chicks were inversely (P less than .05) related to the level of the dietary protein. Body composition data seemed to support a positive (P less than .05) relationship between dietary protein and total carcass protein and an inverse (P less than .05) relationship between dietary protein and carcass fat. In vitro lipogenesis was greater (P less than .05) in chicks fed an 18% protein diet than in chicks fed either 23 or 30% protein diets. Restricted. Protein levels had no effect on lipogenesis in chicks fed on a restriction regime but regulated lipogenesis in chicks fed on the rotational regime. Fatty acid synthetase, malic enzyme and isocitrate dehydrogenase activities, when measured during the rotational regime, were greatest following the 12% diet and least following the 30% diet. Enzyme activities, determined during the restriction regime, were greatest (P less than .05) after 1 day of refeeding and least (P less than .05) after 1 day of feed withdrawal. Measurement of net glucose production in vitro indicated that high-protein diets and feed withdrawal stimulated production of glucose.