This study explored the variation of ileal endogenous amino acid (IEAA) losses and its influencing factors in chickens offered nitrogen-free diets (NFD) containing different ratios of amylose to amylopectin (AM/AP). A total of 252 broiler chickens at 28 d old were randomly allocated into 7 treatment groups for a 3-d trial. The dietary treatments included a basal diet (control), a NFD containing corn starch (CS), and 5 NFD with AM/AP ratios of 0.20, 0.40, 0.60, 0.80, and 1.00, respectively. As the AM/AP ratio increased, the IEAA losses of all AAs, starch digestibility and maltase activity linearly decreased (P < 0.05), but the DM digestibility linearly and quadratically decreased (P < 0.05). Compared with the control, the NFD increased the number of goblet cells and its regulatory genes mucin-2 and krüppel-like factor 4 (KLF-4) while decreasing serum glucagon and thyroxine concentrations, ileal villus height, and crypt depth (P < 0.05). Additionally, NFD with lower AM/AP ratios (0.20 and 0.40) decreased the ileal microbiota species richness (P < 0.05). In all NFD groups, the number of Proteobacteria increased whereas the abundance of Firmicutes dropped (P < 0.05). However, the broilers in the AM/AP 0.60 group were closer to the digestive physiological state of chickens fed the control diet, with no significant change in maltase activity and mucin-2 expression (P < 0.05). In conclusion, increasing AM/AP ratio in a NFD decreased the IEAA losses and the apparent ileal digestibility of starch but inevitably resulted in malnutrition and disruption of gut microbiota homeostasis. This study recommends AM/AP in NFD at 0.60 to measure IEAA of broiler chickens.

本研究探讨了含有不同直链淀粉与支链淀粉比例（AM/AP）的无氮日粮（NFD）鸡回肠内源氨基酸（IEAA）损失的变化及其影响因素。总共252只28日龄肉鸡被随机分为7个治疗组进行3天的试验。饮食治疗包括基础饮食（对照）、含有玉米淀粉（CS）的 NFD 和 AM/AP 比率分别为 0.20、0.40、0.60、0.80 和 1.00 的 5 NFD。随着 AM/AP 比值的增加，IEAA 所有 AA 损失、淀粉消化率和麦芽糖酶活性呈线性下降（P  < 0.05），但 DM 消化率呈线性和二次方下降（P < 0.05）。与对照组相比，NFD 增加了杯状细胞及其调节基因 mucin-2 和 krüppel 样因子 4 ( KLF-4 )的数量，同时降低了血清胰高血糖素和甲状​​腺素浓度、回肠绒毛高度和隐窝深度 ( P  < 0.05 ）。此外，AM/AP 比率较低（0.20 和 0.40）的 NFD 降低了回肠微生物群物种丰富度（P  < 0.05）。在所有 NFD 组中，变形菌门的数量增加，而厚壁菌门的丰度下降（P  < 0.05）。而 AM/AP 0.60 组肉鸡的消化生理状态更接近对照日粮鸡的消化生理状态，麦芽糖酶活性和 mucin-2 表达无显着变化（P < 0.05）。总之，增加 NFD 中的 AM/AP 比率可减少 IEAA 损失和淀粉的表观回肠消化率，但不可避免地导致营养不良和肠道微生物群稳态破坏。本研究建议 NFD 中的 AM/AP 为 0.60，以测量肉鸡的 IEAA。