Economically optimal dietary crude protein and lysine levels for starting broiler chicks

An experiment was conducted to quantify the growth response of broiler chicks to cumulative dietary 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 intake and quadratic effects of dietary lysine intake on body weight gain (BWG), confirming that a diminishing response (marginal BWG decreased as intake of dietary lysine increased) existed (R2 = 0.92 and 0.95, respectively). A significant interaction between dietary CP and lysine for BWG complicates economic modeling because responses must be considered together. A quadratic growth response equation describing BWG as a function of dietary lysine and CP intake was used to develop and demonstrate a quadratic programming model. In general, increasing the price of soybean meal (SBM) decreased the dietary CP concentrations that gave maximum BWG and the concentration of dietary lysine decreased proportionally. In SBM-based diets, the concentration of dietary lysine 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 from using maximum-profit vs. least-cost formulation models could approach 637,000 dollars per year for a single model poultry complex under some economic situations for the starter diet alone.