DataSheet_1_Meta-analysis of the effect of low-protein diets on the growth performance, nitrogen excretion, and fat deposition in broilers.docx

In broilers, the effects of crude protein (CP) reduction on animal performance are heterogeneous. This could limit the use of this strategy in commercial farms despite its potential to improve the sustainability of production. The objective of this meta-analysis was to study the effect of lowering dietary CP in fast-growing broilers with a focus on growth performance. A database was built from 29 papers published after 2016, for a total of 106 trials and 268 treatments. To be included in the database, trials had to be iso-energy and iso-lysine. Trials in which the growth rate for the control treatment was below 90% of the genetic potential of the birds were not included. The effect of the CP level was analyzed by multiple linear regression, with the trial as a random effect. A subsample of 33 trials (AACON) met the recommended amino acid (AA)-to-lysine ratios for indispensable AAs. In this subdatabase, average daily gain and average daily feed intake were maintained when dietary CP was reduced. The feed conversion ratio increased by 1.3% when CP was reduced by a one percentage point. The same CP reduction decreased daily nitrogen (N) excretion by 10.4%, whereas N retention was not affected by CP. In conclusion, respecting the ideal protein concept with the use of feed-grade AA allows for a decrease in dietary CP and N excretion with a limited impact on growth performance.

在肉鸡养殖中，降低粗蛋白质（crude protein, CP）水平对肉鸡生产性能的影响存在异质性。尽管该策略具备提升养殖生产可持续性的潜力，但这种异质性可能限制其在商业养殖场中的应用。本荟萃分析（meta-analysis）旨在探究饲粮粗蛋白质水平降低对快速生长型肉鸡的影响，重点关注其生长性能。本研究构建的数据库涵盖2016年后发表的29篇文献，共纳入106组试验、268个处理组。纳入本数据库的试验需满足等能、等赖氨酸的条件，且对照组肉鸡生长速率不得低于其遗传潜力的90%，未满足上述条件的试验将被排除。本研究以试验为随机效应，采用多元线性回归分析粗蛋白质水平的影响效应。其中33组试验（AACON子样本）满足必需氨基酸（amino acid, AA）与赖氨酸的推荐配比标准。在该子数据库中，当饲粮粗蛋白质水平降低时，肉鸡的平均日增重与平均日采食量保持稳定；粗蛋白质每降低1个百分点，饲料转化率将提升1.3%。同等幅度的粗蛋白质降低可使每日氮排泄量减少10.4%，但氮存留量不受粗蛋白质水平变化的影响。综上，通过使用饲料级氨基酸并遵循理想蛋白质模式，可在对生长性能影响有限的前提下，降低饲粮粗蛋白质水平与每日氮排泄量。