Candida tropicalis ZD-3 prevents excessive fat deposition by regulating ileal microbiota and bile acids enterohepatic circulation in broilers

Evidence suggests that dietary intake of Candida tropicalis ZD-3 (C. tropicalis ) has various health benefits. However, the treatment effect and mechanism remain unclear. The purpose of this study was to evaluate the effect of C. tropicalis on reducing fat deposition in yellow-feathered broilers and to explore its mechanism of action on fat metabolism and deposition in yellow-feathered broilers through the regulation of gut microbiota, affecting bile acids (BAs) metabolism, and altering hepatic lipid structure. A total of 180 1-day-old yellow-feathered broilers were randomly assigned to three groups: CON group fed with normal chow diet, viable C. tropicalis ZD-3 (ZD) group supplemented with ZD, and heat-inactivated C. tropicalis ZD-3 (HZD) group supplemented with HZD. The results showed that ZD and HZD reduced body weight gain and abdominal fat rate, and significantly improved serum and hepatic lipid abnormalities in broilers. ZD and HZD improved the gut microbial composition and significantly reduced the Firmicutes to Bacteroidetes ratio (F/B ratio) in the ileum. In particular, Jeotgalicoccus and Ignatzschineria may be a potential biomarker for effective cholesterol reduction. ZD and HZD attenuated hepatic cholesterol accumulation and regulated lipid metabolism through a combination of decreased ileal FXR-FGF19 signaling via the gut microbiota-BA-FXR pathway and increased hepatic FXR-SHP signaling. ZD and HZD also changed hepatic lipid composition, and the difference was mainly reflected in PC and TG classes, thus regulating hepatic fat deposition by promoting TG degradation and modulating the signal transduction of the cell membrane. Overall, C. tropicalis was effective in improving lipid metabolism in yellow-feathered broilers, and this effect was partly attributed to the regulation of gut microbial composition and metabolites related to BAs metabolism. Our findings provide a theoretical basis for the industrial development of probiotics and their regulation of lipid metabolism in broilers .