Research on low-protein-level diets has indicated that even though the profiles of essential amino acids (EAAs) follow the recommendation for a normal-protein-level diet, broilers fed low-protein diets failed to achieve productive performance compared to those fed normal diets. Therefore, it is imperative to reassess the optimum profile of EAAs in low-protein diets and establish a new ideal pattern for amino acid balance. Furthermore, identifying novel sensitive biomarkers for assessing amino acid balance will greatly facilitate the development of amino acid nutrition and application technology. In this study, 12 dietary treatments [Con(+), Con(-), L&A(-), L&A(+), M&C(-), M&C(+), BCAA (-), BCAA(+), Thr(-), Thr(+), Trp(-) and Trp(+)] were established by combining different EAAs including lysine and arginine, methionine and cysteine, branched-chain amino acid (BCAA), threonine, and tryptophan to observe the growth and development of the broiler chickens fed with low-protein-level diets. Based on the biochemical parameters and untargeted metabolomic analysis of animals subjected to different treatments, biomarkers associated with optimal and suboptimal amino acid balance were identified. Growth performance, carcass characteristics, hepatic enzyme activity, serum biochemical parameters, and breast muscle mRNA expression differed significantly between male and female broilers under different dietary amino acid patterns. Male broilers exhibited higher sensitivity to the adjustment of amino acid patterns than female broilers. For the low-protein diet, the dietary concentrations of lysine, arginine, and tryptophan, but not of methionine, cystine, or threonine, needed to be increased. Therefore, further research on individual BCAA is required. For untargeted metabolomic analysis, Con(+) was selected as a normal diet (NP) while Con(-) represented a low-protein diet (LP). L&A(+) denotes a low-protein amino acid balanced diet (LPAB) and Thr(+) represents a low-protein amino acid imbalance diet (LPAI). The metabolites oxypurinol, pantothenic acid, and D-octopine in birds were significantly influenced by different dietary amino acid patterns. Adjusting the amino acid profile of low-protein diets is required to achieve normal growth performance in broiler chickens fed normal-protein diets. Oxypurinol, pantothenic acid, and D-octopine have been identified as potentially sensitive biomarkers for assessing amino acid balance.

中文翻译：

---

肉鸡低蛋白日粮中氨基酸谱和氨基酸平衡的相对生物标志物的评估


对低蛋白水平饮食的研究表明，尽管必需氨基酸 （EAA） 的概况遵循正常蛋白质水平饮食的建议，但与饲喂正常饮食的肉鸡相比，饲喂低蛋白饮食的肉鸡未能达到生产性能。因此，当务之急是重新评估低蛋白饮食中 EAA 的最佳概况，并建立氨基酸平衡的新理想模式。此外，识别用于评估氨基酸平衡的新型敏感生物标志物将极大地促进氨基酸营养和应用技术的发展。本研究通过组合赖氨酸和精氨酸、蛋氨酸和半胱氨酸、支链氨基酸 （BCAA）、苏氨酸和色氨酸等不同必需氨基酸，建立了 12 种日粮处理 [Con（+）、Con（-）、L&A（-）、L&A（+）、M&C（-）、M&C（+）、BCAA（-）、Thr（-）、Thr（+）、Thr（+）、Trp（-） 和 Trp（+）]，以观察饲喂低蛋白饮食的肉鸡的生长发育情况。基于接受不同处理的动物的生化参数和非靶向代谢组学分析，确定了与最佳和次优氨基酸平衡相关的生物标志物。在不同日粮氨基酸模式下，雄肉鸡和母肉鸡的生长性能、胴体特性、肝酶活性、血清生化指标和乳房肌肉 mRNA 表达差异显著。雄性肉鸡比雌性肉鸡对氨基酸模式的调整表现出更高的敏感性。对于低蛋白饮食，需要增加赖氨酸、精氨酸和色氨酸的膳食浓度，但不需要增加蛋氨酸、胱氨酸或苏氨酸的浓度。因此，需要对单个 BCAA 进行进一步研究。 对于非靶向代谢组学分析，Con（+） 被选为正常饮食 （NP），而 Con（-） 代表低蛋白饮食 （LP）。L&A（+） 表示低蛋白氨基酸平衡饮食 （LPAB），Thr（+） 表示低蛋白氨基酸不平衡饮食 （LPAI）。鸟类的代谢物羟嘌呤醇、泛酸和 D-章鱼碱受不同膳食氨基酸模式的显著影响。需要调整低蛋白日粮的氨基酸谱，才能在饲喂正常蛋白日粮的肉鸡中实现正常生长性能。氧嘌呤醇、泛酸和 D-octopine 已被确定为评估氨基酸平衡的潜在敏感生物标志物。