低蛋白质饲粮中添加半胱氨酸对肉仔鸡生长性能、胴体组成、血清生化指标及氮代谢的影响

Effects of Cysteine Supplementation in Low Protein Diet on Growth Performance,Carcass Composition,Serum Biochemical Parameters and Nitrogen Metabolism of Broilers

本试验旨在研究低蛋白质(LP)饲粮中添加半胱氨酸(Cys)对肉仔鸡生长性能、胴体组成、血清生化指标及氮代谢的影响,以确定肉仔鸡LP饲粮中Cys的适宜添加水平。选取432只1日龄、体重相近的健康爱拔益加(AA)肉仔鸡公雏,随机分为6个组,每组6个重复,每个重复12只鸡。正对照(PC)组饲喂基础饲粮[前期(1~21日龄)和后期(22~42日龄)蛋白质水平分别为22%和20%],负对照(NC)组的蛋白质水平在PC组的基础上降低4.5个百分点(前期和后期蛋白质水平分别为17.5%和15.5%),Cys组在NC组的基础上分别添加0.05%、0.10%、0.15%和0.20%的Cys。各组前期和后期总含硫氨基酸水平分别为0.83%和0.79%。试验期42 d,分为前期和后期2个阶段。结果表明:1)饲粮蛋白质水平降低4.5个百分点,21和42日龄肉仔鸡的平均体重(ABW)、各生长阶段的平均日增重(ADG)和平均日采食量(ADFI)均显著降低(P<0.05),试验前期的料重比(F/G)显著提高(P<0.05);添加0.10%和0.15%Cys后,21和42日龄的ABW、试验后期和试验全期的ADG和ADFI均显著提高(P<0.05),且均随Cys添加水平的提高呈线性和二次提高(P<0.05),试验前期的F/G显著降低(P<0.05),达到了与PC组相似的生长性能。2)饲粮添加Cys未见显著影响42日龄肉仔鸡的全净膛率(EP)和腿肌率(LMP)(P>0.05),但有提高LMP的趋势(0.05≤P<0.10);饲粮添加Cys线性和二次降低胸肌率(BMP)(P<0.05),腹脂率(AFP)显著提高(P<0.05)。3)饲粮添加Cys对21和42日龄肉仔鸡的血清生化指标无显著影响(P>0.05)。4)饲粮添加Cys显著降低19~21日龄和40~42日龄肉仔鸡的氮摄入量、氮排泄量和氮存留量(P<0.05),显著提高19~21日龄的氮存留率(P<0.05)。5)二次曲线拟合结果表明,LP饲粮中Cys添加水平为0.13%~0.17%时,生长性能和氮代谢最佳。综上所述,LP饲粮中添加0.15%Cys能改善肉仔鸡的体增重、采食量和F/G,提高氮存留率;以生长性能和氮代谢为判断指标,推荐肉仔鸡LP饲粮中Cys的适宜添加水平为0.13%~0.17%(Cys占总含硫氨基酸的比例为45%~49%)。

This experiment was conducted to investigate the effects of cysteine(Cys)supplementation in low protein(LP)diet on growth performance,carcass composition,serum biochemical parameters and nitrogen metabolism of broilers,in order to determine the optimal supplemental level of Cys in LP diet of broilers.Four hundred and thirty-two 1-day-old healthy Arbor Acres(AA)male broilers with similar body weight were randomly allotted into 6 groups with 6 replicates per group and 12 broilers per replicate.The broilers in positive control(PC)group were fed the basal diet(the protein levels in early stage during 1 to 21 days of age and later stage during 22 to 42 days of age were 22%and 20%,respectively),the protein level of negative control(NC)group was reduced by 4.5%on the basis of PC group(the protein levels in early stage and later stage were 17.5%and 15.5%,respectively),and those in Cys groups were supplemented with 0.05%,0.10%,0.15%and 0.20%Cys on the basis of the NC group,respectively.The levels of total sulfur amino acid were 0.83%and 0.79%in early stage and later stage,respectively.The experiment lasted for 42 days with 2 periods.The results showed as follows:1)the protein level in diet reduced by 4.5%significantly decreased average body weight(ABW)of broilers at 21 and 42 days of age and average daily gain(ADG)and average daily feed intake(ADFI)during all stages(P<0.05),significantly increased the ratio of feed to gain(F/G)during early stage(P<0.05).Adding 0.10%and 0.15%Cys to LP diet significantly increased ABW at 21 and 42 days of age and ADG and ADFI during later stage and whole stage(P<0.05),and all of them increased linearly and quadratically with Cys supplemental level increasing(P<0.05),significantly decreased F/G during early stage(P<0.05),the addition of Cys recovered growth performance fed LP diet to similar level of that in PC group.2)LP diet supplemented Cys did not significantly affected eviscerated percentage(EP)and leg muscle percentage(LMP)(P>0.05),but tended to increased LMP of broilers at 42 days of age(0.05≤P<0.10).LP diet supplemented Cys linearly and quadratically decreased breast muscle percentage(BMP)(P<0.05),and significantly increased abdominal fat percentage(AFP)(P<0.05).3)No significant differences in serum biochemical parameters were observed among all groups of broilers at 21 and 42 days of age(P>0.05).4)LP diet supplemented Cys significantly decreased nitrogen intake,nitrogen excretion and nitrogen retention rate of broilers during 19 to 21 days of age and 40 to 42 days of age(P<0.05),and significantly elevated nitrogen retention rate during 19 to 21 days of age(P<0.05).5)The quadric curve fitting results showes that optimal Cys supplemental level in LP diet for the best growth performance and nitrogen metabolism was 0.13%to 0.17%.In conclusion,LP diet supplemented 0.15%Cys can improve body weight gain,feed intake and F/G of broilers,and elevate nitrogen retention rate.Based on growth performance and nitrogen metabolism,the Cys supplemental level in LP diet of broilers is recommended to be 0.13%to 0.17%(Cys accounts for 45%to 49%of total sulfur amino acids).