摘要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.