Dietary bile acids improve breast muscle growth in chickens through FXR/IGF2 pathway

Abstract Background Fast-growing broiler chickens are commonly fed diets with high-fat content, particularly in integrated farms in Northeast China. Therefore, the efficiency of fat digestion, absorption, and utilization is critical for broiler meat production. Bile acids (BA) promote fat digestion and absorption, yet whether and how BA affects muscle growth in broiler chickens remain unclear. Results In this study, one-day-old broiler chickens were fed diets of low, medium, and high levels of crude fat with or without BA supplementation, for 42 days (d). Chickens fed BA-supplemented high-fat diet had significantly ( P < 0.05) higher body weight (BW) at 21 d and average daily gain (ADG) from 1 to 21 d, compared to all the other groups. Feed conversion rate (FCR) was significantly ( P < 0.05) lower in high-fat group, which was further decreased ( P < 0.05) with BA supplementation. The improved growth performance in BA-supplemented high-fat group was associated with significantly ( P < 0.05) increased lipase activity in the chyme of small intestine, a trend of decrease ( P = 0.06) in abdominal fat ratio, and significantly ( P < 0.05) higher breast muscle mass. Further histological analysis revealed significant ( P < 0.05) increases in myofiber diameter, cross-sectional area, as well as RNA and DNA content in the breast muscle of BA-supplemented broiler chickens on high-fat diet. Accordantly, genes related to muscle growth, including mTOR, MYH1B, and PAX7, are significantly ( P < 0.05) upregulated. These changes were accompanied by significantly ( P < 0.05) increased concentration of insulin-like growth factor 2 (IGF2) in serum, liver and breast muscle. The upregulation of IGF2 gene in the breast muscle of broiler chickens fed BA-supplemented high-fat diet was associated with significantly ( P < 0.05) increased FXR protein content and FXR binding to IGF2 gene promoter. Conclusions These results suggest that dietary BA supplementation improves FCR and breast muscle growth through FXR-mediated IGF2 pathway in broiler chickens fed high-fat diet.