Effects of Dietary Metabolizable Energy and Protein on Early Growth Responses of Broilers to Dietary Lysine1

ABSTRACT Two studies evaluated effects of metabo-lizable energy (ME), digestible Lys (dLys), and amino acid (AA) balance on broiler performance. In experiment 1 diets contained 3 levels of ME (3,000, 3,100, and 3,200 kcal/kg) in combination with 4 levels of dLys (1.05, 1.13, 1.21, and 1.29%). A fixed proportion of dLys relative to CP and key indispensable AA was maintained in graded increments of CP from 21.9 to 26.9%. There was no interac-tion of ME and dLys for 21 d BW gain or adjusted feed conversion ratio, which improved linearly with dietary dLys. Increasing the dLys or ME had no effect on feed intake, and the linear improvement in performance was attributed to a step-wise increase in dLys when diets contained a balance of AA and CP. Experiment 2 evalu-ated broiler response to 20 d of age when diets contained graded increments in dLys while maintaining a fixed pro-portion of dLys relative to CP and indispensable A