Porcine bile acids improve performance by altering hepatic lipid metabolism and amino acid metabolism with different protein level diets in late laying hens.

As the extension of the egg-laying cycle, heightened energy and lipid metabolism cause excessive lipid accumulation, resulting in rapid decline in laying performance during the late laying period. Bile acids (BAs), synthesized from cholesterol in the liver, are potent metabolic and immune signaling molecules involved in lipid metabolism and the regulation of energy homeostasis. However, under different dietary protein levels, the role of BAs on hepatic lipid metabolism of laying hens at the late phase remains unclear. This experiment aimed to evaluate the effects of porcine BAs supplementation on performance, lipid metabolism, antioxidant status and amino acid metabolism in late-phase laying hens fed diets with different protein level. A total of 192 Hy-Line Brown laying hens (62 weeks of age) were randomly assigned to one of four treatment groups, in a 2 × 2 factorial design, with 8 replicates per treatment. The hens were fed diets with either normal protein (16.42 %) or low-protein (15.35 %) levels, with or without BAs supplementation (120 mg/kg for the first 56 days, followed by 200 mg/kg for the next 42 days). The results demonstrated that dietary BAs supplementation significantly enhanced egg production and feed intake (P < 0.05) although it has no notable effect on egg quality. Bile acids supplementation effectively reduced liver total cholesterol (TC), triglyceride (TG), as well as malondialdehyde (MDA) levels, while also ameliorating lipid deposition through the regulation of expression of lipid metabolism-related genes in late laying hens (P < 0.05). Additionally, the low-protein diets downregulated amino acid catabolism, thereby reducing serum uric acid content and enhancing protein utilization. Further analysis revealed that BAs also positively influenced trypsin activity and increased the expression of amino acid transporters, thereby improving amino acid availability (P < 0.05). In conclusion, this study demonstrated that dietary BAs supplementation could enhance the laying performance in late laying hens, primarily by improving hepatic lipid metabolism, antioxidant capacity, and amino acid availability.