The development of skeletal muscle is a crucial factor in determining the meat yield and economic benefits of broiler production. Recent research has shown that mulberry leaves and their extracts can be used to significantly improve the growth performance of livestock and poultry. The present study aims to elucidate the mechanisms involved in the regulation of skeletal muscle development in broiler offspring by dietary mulberry-leaf flavonoids (MLF) supplementation from the perspective of maternal effect theory. A total of 270 Qiling broiler breeder hens were randomly assigned to 3 treatments with different doses of MLF (0, 30, 60 mg/kg) for 8 weeks before collecting their fertilized eggs. The chicken offspring at 13 and 19 d of embryonic stage, and from 1 to 28 d old after hatching were included in this study. The results showed that maternal supplementation increased the breast muscle weight and body weight of the offspring at the embryo and chick stages (P < 0.05). This was followed by increased cross-sectional area of pectoral muscle fibres at 14 d (P < 0.05). Further determination revealed a tendency towards increased serum levels of insulin-like growth factor 1 (IGF-1) (P = 0.092) and muscle fibre count (P = 0.167) at 1 d post-hatching following maternal MLF treatment, while serum uric acid (UA) was decreased at 14 d after hatching (P < 0.05). Moreover, maternal MLF supplementation significantly up-regulated the mRNA expression of the myogenic regulatory factor Myf5 in skeletal muscle at the both embryonic and growth stages (P < 0.05). The relative abundance of the downstream protein of BMPR2, Smad1 and p-Smad1/5/9 in the TGFβ signalling pathway was significantly increased by maternal MLF treatment. Meanwhile, the increased expression of the target protein p-mTOR in the breast muscle of the offspring chicks is in accordance with the improved growth rate of the breast and the body. In conclusion, maternal MLF supplementation can promote muscle protein metabolism and muscle fibre development of chick embryos through upregulation of Myf5 expression and BMP/p-Smad1/5/9 axis, thereby improving growth performance of slow growing broiler.

中文翻译：

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母体补充桑叶类黄酮可改善鸡后代骨骼肌的发育


骨骼肌的发育是决定肉鸡产量和肉鸡生产经济效益的关键因素。最近的研究表明，桑叶及其提取物可用于显着改善畜禽的生长性能。本研究旨在从母体效应理论的角度阐明日粮桑叶黄酮 （MLF） 补充剂对肉鸡后代骨骼肌发育的调节机制。将 270 只麒麟种鸡随机分配到 3 次不同剂量 MLF （0、30、60 mg/kg） 处理，持续 8 周，然后收集受精蛋。本研究包括胚胎期 13 和 19 d 以及孵化后 1 至 28 d 的鸡后代。结果表明，母体补充增加了胚胎和雏鸡阶段后代的乳房肌肉重量和体重 （P < 0.05）。随后在 14 d 时胸肌纤维横截面积增加 （P < 0.05）。进一步测定显示，母体 MLF 处理后 1 天血清胰岛素样生长因子 1 （IGF-1） （P = 0.092） 和肌纤维计数 （P = 0.167） 水平增加，而血清尿酸 （UA） 在孵化后 14 天降低 （P < 0.05）。此外，母体 MLF 补充剂在胚胎期和生长期均显著上调骨骼肌中生肌调节因子 Myf5 的 mRNA 表达 （P < 0.05）。母体 MLF 处理显著增加了 TGFβ 信号通路中下游蛋白 BMPR2 、 Smad1 和 p-Smad1/5/9 的相对丰度。 同时，靶蛋白 p-mTOR 在子代雏鸡乳房肌肉中的表达增加与乳房和身体生长速度的提高相一致。综上所述，母体 MLF 补充剂可通过上调 Myf5 表达和 BMP/p-Smad1/5/9 轴促进雏鸡胚胎的肌肉蛋白代谢和肌纤维发育，从而提高慢速生长肉鸡的生长性能。