Dietary bile acids supplementation reduces eggshell translucency and improves eggshell quality in late-phase laying hens.

Extended laying cycles in hens lead to declines in production performance, health status, and egg quality, which raises concerns about animal welfare and food safety. This study investigated the effects of dietary bile acids (BAs) supplementation on production performance and eggshell quality in late-phase laying hens. A total of 320 62-wk-old Hy-Line Gray laying hens were randomly assigned to four groups and fed a basal diet or a basal diet supplemented with 200, 500, or 800 mg/kg BAs for 6 wk. Dietary supplementation with 800 mg/kg BAs significantly reduced eggshell translucency grade, increased eggshell thickness and percentage, and decreased egg weight loss during storage. Transcriptomic analysis of the isthmus revealed that BAs downregulated matrix-degrading enzyme MMP9 and inflammatory regulator TNFRSF1B, while modulating extracellular matrix-related genes. HE staining of uterine tissue showed that there were a large number of vacuoles in the gland in the CON group, while in the 800 mg / kg BAs group, the cells in the gland were closely arranged without obvious vacuoles. TUNEL staining showed brown apoptotic positive cells in the CON group, while the apoptotic cells in the 800 mg/kg BAs group were significantly reduced. Moreover, BAs exerted beneficial effects by enhancing antioxidant capacity (T-AOC, SOD), inhibiting pro-inflammatory cytokines (IFN-γ, IL-1β), and promoting Ca²⁺ utilization within the uterus. Collectively, these findings demonstrate that dietary BAs, particularly at 800 mg/kg, effectively reduce eggshell translucency in aged laying hens. This improvement is associated with the preservation of shell membrane integrity via downregulation of ECM-degrading enzymes in the isthmus, and the enhancement of calcification through alleviation of oxidative stress and inflammation in the uterus.