The current study aimed to compare the effects of increasing concentrations of dietary threonine (Thr), tryptophan (Trp), and glycine (Gly) on growth performance, stress biomarkers, and intestinal function in broiler chickens under multiple stress conditions. Five hundred sixty broiler chickens at 21 d old were randomly allotted to 5 treatments with 8 replicates. Birds in a positive control (PC) treatment were raised under low stock density (16.9 birds/m2 per cage) with recommended environmental conditions, whereas birds in 4 treatments were subjected to multiple stress conditions: a cyclic heat stress of 30 ± 0.3 °C for 10 h and 23 ± 0.2 °C for 14 h per day with high stock density (25.3 birds/m2 per cage). A basal diet was assigned to both PC and negative control (NC) treatments. Three additional diets were individually formulated to contain double concentrations of digestible Thr, Trp, or Gly + Ser compared with their concentrations in the basal diet. The experiment lasted for 14 d. Results showed that NC treatment had less growth performance (P < 0.001), jejunal goblet cell counts (P = 0.018), and trans-epithelial electrical resistance (TEER; P < 0.001), but greater (P = 0.026) feather corticosterone (CORT) concentrations than PC treatment. Thr treatment showed the least (P < 0.001) feed conversion ratio (FCR) among treatments under multiple stress conditions. Thr, Trp, and Gly treatments had less (P = 0.026) feather CORT concentrations, but had greater (P < 0.001) TEER than NC treatment. In conclusion, increasing concentrations of dietary Thr, Trp, or Gly improve the growth performance and intestinal health in broiler chickens with decreasing stress response under multiple stress conditions.

中文翻译：

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日粮苏氨酸、色氨酸和甘氨酸浓度的增加可改善在多种应激条件下饲养的肉鸡的生长性能和肠道健康，同时减少应激反应


本研究旨在比较日粮苏氨酸 （Thr）、色氨酸 （Trp） 和甘氨酸 （Gly） 浓度增加对多种应激条件下肉鸡生长性能、应激生物标志物和肠道功能的影响。将 560 只 21 d 龄的肉鸡随机分配到 5 个处理，每个处理 8 个重复。阳性对照 （PC） 处理的鸡在推荐的环境条件下在低存量密度（每笼 16.9 只鸡/m2）下饲养，而 4 个处理中的鸡鸡受到多种胁迫条件：30 ± 0.3 °C 持续 10 小时和 23 ± 0.2 °C 持续每天 14 小时，存量密度高（每个笼 25.3 只鸡/m2）。基础饮食被分配给 PC 和阴性对照 （NC） 治疗。与基础日粮中的浓度相比，三种额外的日粮被单独配制，含有双倍浓度的可消化 Thr、Trp 或 Gly + Ser。实验持续 14 d。结果显示，NC 处理的生长性能较低 （P < 0.001）、空肠杯状细胞计数 （P = 0.018） 和跨上皮电阻 （TEER;P < 0.001），但羽毛皮质酮 （CORT） 浓度高于 PC 处理 （P = 0.026）。在多种胁迫条件下，Thr 处理显示最低 （P < 0.001） 饲料转化率 （FCR）。Thr、Trp 和 Gly 处理的羽毛 CORT 浓度较低 （P = 0.026），但比 NC 处理具有更高的 （P < 0.001） TEER。总之，增加日粮 Thr、Trp 或 Gly 的浓度可以改善肉鸡的生长性能和肠道健康，同时在多种应激条件下降低应激反应。