Dietary crude protein and lysine in broiler chicken nutrition
Sterling, Kimberly Gruwell
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The effect of dietary crude protein (CP) and lysine on broiler chicken performance was investigated in this dissertation. Four studies were conducted to better understand the relationship between dietary CP and lysine with emphasis on dietary CP level and source on broiler chicken performance and the lysine requirement, dietary CP and lysine level and broiler genotype interactions, and the growth response of boiler chickens to cumulative dietary CP and lysine intakes. Increasing dietary CP from 17 to 26% was found to increase body weight gain (BWG) and improve feed conversion ratio (FCR) in male broiler chicks. Dietary CP level and/or source had significant effects on carcass composition. Males and females were found to have similar qualitative responses to increasing dietary CP and source. The response of broiler chicks to graded levels of lysine at 17, 18.5, and 23% CP was measured in diets mixed by either the graded supplementation or diet dilution method. The requirement for lysine was estimated as a percentage of the diet and as a percentage of the dietary CP level. Results of a t-test show that the lysine requirement between dietary CP levels were significantly different on a percentage of diet basis but not as a percentage of dietary CP level. These results indicate that the lysine requirement is a direct proportion of the dietary CP level within a practical range. In addition, no differences were observed between the graded supplementation method and the diet dilution method in estimating the lysine requirement. A three-way interaction between dietary CP, lysine and genotype was detected in broiler chicks during the starter and grower phases. Ross 308 and Cobb x Cobb broiler chicks were fed starter diets containing two dietary CP levels and three dietary lysine levels. Ross 508 and Arbor Acres broiler chicks were fed grower diets with similar dietary CP and lysine levels. Regression analysis showed differences due to genotype for BWG, feed intake and FCR for starter chicks, and BWG and carcass composition for grower chicks. The three-way interaction demonstrates that quantitative differences exist between genotypes in response to increasing dietary CP and lysine levels. The response of broiler chicks to cumulative dietary CP and lysine intakes was determined to follow "the law of diminishing returns." Significant linear and quadratic responses were observed with chicks fed starter diets with four levels of dietary CP and lysine. BWG as a function of dietary CP and lysine intake was used to develop and demonstrate a quadratic feed formulation programming model. In general, as the price of crude protein sources increased, the level of dietary CP decreased. Maximum profit diets formulated using the quadratic program could significantly increase returns over the least-cost formulation models under some economic situations for the starter diet alone.