Digestible lysine levels obtained by two methods of formulation of diets for 22-to-42-day-old broilers

The objective of this study was to evaluate the effect of digestible lysine levels in diets with or without supplementation of industrial amino acids on performance, carcass characteristics and nitrogen excretion in broilers of 22 to 42 days of age. Birds were distributed in a completely randomized experimental design in a 4 × 2 factorial arrangement, with four digestible lysine levels (9.0, 10.0, 11.0 and 12.0 g/kg) and two methods to obtain the lysine levels (variation in the proportion of corn and soybean meal, without supplementation; or supplementation of industrial amino acids), eight replicates and 20 birds per replicate. There was an interaction effect on the performance characteristics and on the weights and yields of prime cuts. In both diets, feed conversion improved linearly as the lysine levels were increased. Feed intake; weight gain; carcass, thigh and drumstick weights; and boneless breast yield increased and abdominal fat reduced linearly as the lysine levels were increased in the unsupplemented diet. The lysine levels of the supplemented diets linearly reduced the yield of drumstick and quadratically reduced the yields of bone-in and boneless breast up to the estimated levels of 10.4 and 10.7 g/kg, respectively. Diets without supplementation increased the excretion and retention of nitrogen. The levels of 9.0 and 12.0 g/kg digestible lysine obtained with supplementation of industrial amino acids and without it, respectively, provide the best performance and yield of prime cuts in the birds. Diets in which the digestible lysine levels are obtained without supplementation provide better performance responses and carcass characteristics compared with supplemented diets.

本研究旨在评估日粮中可消化赖氨酸（digestible lysine）水平（无论是否添加工业氨基酸（industrial amino acids））对22~42日龄肉鸡生产性能、屠宰性状及氮排泄量的影响。试验采用完全随机试验设计（completely randomized experimental design），设置4×2因子设计方案，包含4个可消化赖氨酸水平（9.0、10.0、11.0及12.0 g/kg），以及2种赖氨酸水平调控方式：通过调整玉米与豆粕配比且不添加外源氨基酸，或添加工业氨基酸；每个处理设置8个重复，每个重复饲养20只肉鸡。
试验结果显示，生产性能指标以及优质分割肉（prime cuts）的重量和产率存在交互效应。两类日粮中，饲料转化率均随赖氨酸水平提升呈线性改善趋势。在不添加外源氨基酸的日粮组中，随着可消化赖氨酸水平升高，肉鸡采食量、日增重、屠体重、腿肌与胫肉重量、无骨胸肉（boneless breast）产率均线性提升，而腹部脂肪含量则线性降低。在添加工业氨基酸的日粮组中，随着赖氨酸水平升高，胫肉产率呈线性下降趋势，带骨胸肉（bone-in breast）和无骨胸肉产率则随赖氨酸水平升高呈二次曲线变化，分别在赖氨酸水平达到估算的10.4 g/kg和10.7 g/kg时达到最高产率。
不添加外源氨基酸的日粮可提升肉鸡的氮排泄量与氮保留量。分别通过添加工业氨基酸和不添加外源氨基酸获得的9.0 g/kg和12.0 g/kg可消化赖氨酸水平，可使肉鸡获得最优的生产性能与优质分割肉产率。相较于添加工业氨基酸的日粮，不添加外源氨基酸的日粮可使肉鸡获得更优异的生产性能与屠宰性状表现。