1307 - METABOLISM AND NUTRITION Responses of Growing...

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METABOLISM AND NUTRITION Responses of Growing Broilers to Diets with Increased Sulfur Amino Acids to Lysine Ratios at Two Dietary Protein Levels S. L. Vieira,* A. Lemme,† ,1 D. B. Goldenberg,* and I. Brugalli* *Departamento de Zootecnia Universidade Federal do Rio Grande do Sul Av. Bento Gonc ¸alves, 7712 Porto Alegre, RS 91540-000 Brazil; and †Degussa AG, Feed Additives Applied Technology, Rodenbacher Chaussee 4, 63457 Hanau-Wolfgang, Germany ABSTRACT An experiment with 1,440 male Cobb 500 and 1,440 male Ross 308 broilers (14 to 35 d of age) was conducted to investigate the effects of diets having 4 levels of digestible methionine plus cysteine (SAA) on various performance criteria at 2 dietary protein levels (20.5 and 26.0%). Two corn-soybean meal/poultry by-product basal diets were formulated to contain 3,060 kcal/kg ME n and either 20.5 or 26.0% balanced protein, and 1.12 and 1.46% digestible (according to table values) lysine, respec- tively. Except for SAA, the ratios between essential amino acids were kept identical in both diets according to the ideal protein concept. The ratio between digestible SAA and digestible Lys was 50%. All remaining nutrients met or exceeded NRC (1994) recommendations. Graded levels of SAA were supplemented to obtain digestible SAA to ( Key words : broiler, methionine, sulfur amino acid, ideal protein, carcass quality) 2004 Poultry Science 83:1307–1313 INTRODUCTION Responses of broilers to dietary amino acids have been extensively studied especially after synthetic forms be- came available allowing easier design of dose-response investigations. In this context, sulfur amino acids (SAA, methionine and cysteine) play a very important role in growing broilers because they are essential for optimum muscle accretion and feather synthesis as well as for some biochemical processes (i.e., as methyl-group donators). However, SAA are often first limiting in common broiler diets. Nutrient recommendations for broiler feeds are usually appropriate to maximize growth. However, opti- mum dietary SAA levels change with the production goal, such as the optimization of growth, breast meat yield, or feed conversion. For instance, optimum SAA levels for breast meat production have been shown to be higher compared with those for whole carcasses or weight gain 2004Poultry Science Association, Inc. Received for publication October 12, 2003. Accepted for publication March 4, 2003. 1 To whom correspondence should be addressed: andreas.lemme@ degussa.com. 1307 Lys ratios of 62, 69, and 77%, with 77% representing an optimized amino acid balance. Increasing the protein level clearly improved weight gain, feed conversion, breast meat yield, and abdominal fat content. Increasing SAA levels resulted in strong nonlinear or linear dose responses at both protein levels and for both strains. Re- gression analysis suggested that reducing digestible SAA in a balanced protein (diets with SAA:Lys of 77%) impairs performance, and that optimum SAA:Lys ratio for grow-
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1307 - METABOLISM AND NUTRITION Responses of Growing...

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