Two experiments are conducted to investigate the effects of low crude protein (CP) amino acid-supplemented diets rnon growth performance,nitrogen (N) excretion and carcass quality of broilers.In experiment 1,six hundred (half males rnand half females) one-day-old Arbor Acre broilers were raised during d 1 to 21,d 22 to 42 and d 43 to 49.Five diets contai-rnning different protein levels were used during each of the three periods including the starter period (22.8%,21.9%,rn21.0%,19.5% and 19.0％ CP,d 1 to 21),grower period (20.1%,18.8%,17.8%,16.5% and 16.0% CP,d 22 to 42) rnand finisher period (18.0%,16.9%,15.9％,15.0% and 13.8% CP,d 43 to 49).All diets were formulated to meet the to-rntal amino acid requirements for methionine,lysine and threonine.In experiment 2,five diets approximately containing the rnCP level as those used in the starter and grower periods in experiment 1 were supplemented with sufficient crystalline amino rnacids to meet the digestible amino acid requirements for all essential amino acids (EAA).The results showed as follows:re-rnducing dietary CP level had no significant effect on growth performance during each period in experiment 1 (P>0.05).In rnexperiment 2,weight gain and feed conversion ratio were both decreased in starter period (P<0.01) but not in the grower rnperiod and the entire period (P>0.05).There were no significant differences in carcass quality among all treatments in rnboth experiments (P>0.05),except that a linear increase in fat deposition occurred as dietary CP was reduced in experi-rnment 1 (P<0.05).Reducing dietary CP level decreased linearly N excretion (P<0.01),and decreased plasma glycine and rnphenylalanine concentrations in experiment 2 (P<0.05).In conclusion,birds fed low protein diets supplemented with ami-rnno acids can produce similar growth and carcass quality to those fed high protein diets in the present study.rnThe present study.%本研究分2个试验,旨在探讨低蛋白质补充合成氨基酸饲粮对肉仔鸡生长性能、氮排泄和胴体品质的影响.试验1选用600只1日龄爱拔益加肉仔鸡(公母各占1/2),分1～21 d,22～42 d和43～49 d 3个阶段饲养,饲粮共设5个处理,粗蛋白质水平分别为:生长前期(1～21 d):22.8%、21.9%、21.0%、19.5%和19.0%;生长中期(22～42 d):20.1%、18.8%、17.8%、16.5%和16.0%;生长后期(43～49 d):18.0%、16.9%、15.9%、15.0%和13.8%.各个处理蛋氨酸、赖氨酸和苏氨酸水平均满足NRC(1994)肉仔鸡营养需要.试验2的5组肉鸡饲粮的蛋白质水平与试验1的生长前期和生长中期饲粮相同,同时补充了足够的合成氨基酸以满足肉仔鸡对所有可消化必需氨基酸的需要量.结果表明:降低饲粮粗蛋白质水平同时补充合成氨基酸不影响试验1各个阶段肉仔鸡的生长性能(P>0.05).当以可消化氨基酸为基础配制饲粮时(试验2),生长前期肉仔鸡的日增重和饲料转化效率得到显著改善(P<0.01),但生长中期和生长全期肉仔鸡日增重和饲料转化效率差异不显著(P>0.05).降低饲粮粗蛋白质水平线性增加了试验1中肉仔鸡的脂肪沉积率(P<0.05),但对其他胴体指标没有显著影响(P>0.05).氮排泄随饲粮粗蛋白质水平的降低而线性减少(P<0.01).此外,降低饲粮粗蛋白质水平还降低了试验2中肉仔鸡血浆甘氨酸和苯丙氨酸的含量(P<0.05).综上所述,降低肉仔鸡饲粮粗蛋白质水平同时补充合成氨基酸可获得使用高蛋白质饲粮时的生长性能和胴体品质.
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