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Unformatted text preview: METABOLISM AND NUTRITION Economically Optimal Dietary Crude Protein and Lysine Levels for Starting Broiler Chicks K. G. Sterling,* D. V. Vedenov,† G. M. Pesti,* ,1 and R. I. Bakalli* *Department of Poultry Science and †Department of Agricultural and Applied Economics, University of Georgia Athens, Georgia 30602-2772 ABSTRACT An experiment was conducted to quantify the growth response of broiler chicks to cumulative di- etary lysine and CP intakes. From d 7 to 17, chicks were fed one combination of dietary lysine and CP (17, 20, 23, and 26% CP and 3.5, 4.0, 4.5, and 5.0 g lysine per 100 g of CP) in a diet containing 3,200 kcal/kg ME. There were significant linear and quadratic effects of dietary CP in- take and quadratic effects of dietary lysine intake on body weight gain (BWG), confirming that a diminishing re- sponse (marginal BWG decreased as intake of dietary lysine increased) existed (R 2 = 0.92 and 0.95, respectively). A significant interaction between dietary CP and lysine for BWG complicates economic modeling because re- sponses must be considered together. A quadratic growth ( Key words : lysine, crude protein, broiler, quadratic programming model) 2005 Poultry Science 84:29–36 INTRODUCTION The concept of feeding economically optimal concen- trations of nutrients based on diminishing returns func- tions is not new but has been rarely used in nutrition (Almquist, 1953). Almquist (1953) used log-linear dimin- ishing returns models to describe 2-dimensional input- output relationships. Several other nonlinear models have been developed to describe diminishing returns functions of nutrient inputs (Pilbrow and Morris, 1974; Lerman and Bie, 1975; Morgan et al., 1975; Robbins et al., 1979). Pesti et al. (1986) used a quadratic polynomial to describe a response model with feed consumption and body weight gain (BWG) as functions of 2 inputs (CP and ME). They observed quadratic growth responses to dietary energy and CP, indicating diminishing marginal productivity. This relationship is an example of nutrient substitution. That is, similar BW can be achieved with varying combi- nations of dietary energy and CP. The relationship be- tween dietary lysine and CP concentrations is not unlike other substitution examples in nutrition, such as phytin 2005 Poultry Science Association, Inc. Received for publication February 28, 2003. Accepted for publication August 29, 2004. 1 To whom correspondence should be addressed: email@example.com. 29 response equation describing BWG as a function of di- etary lysine and CP intake was used to develop and dem- onstrate a quadratic programming model. In general, in- creasing the price of soybean meal (SBM) decreased the dietary CP concentrations that gave maximum BWG and the concentration of dietary lysine decreased proportion- ally. In SBM-based diets, the concentration of dietary ly- sine that maximized BWG was less than or equal to the concentration reached by the proportions of corn and SBM needed to meet dietary CP constraints. Savings fromSBM needed to meet dietary CP constraints....
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This note was uploaded on 07/28/2011 for the course VET 4335 taught by Professor Sakomura during the Spring '11 term at University of South Pacific.
- Spring '11