Bacillus coagulans improves late-laying hen performance through bile acid modulation that suppresses hepatic lipid accumulation and alleviates ovarian oxidative stress

In production, laying hens often accumulate fat in their bodies due to high-fat diets, which in turn affects their production performance. Bacillus coagulans has good tolerance in the digestive system and is beneficial to intestinal health. The objective of this study was to evaluate the effect of Bacillus coagulans on production performance, lipid metabolism, and ovarian function in late-phase laying hens. Research has found that adding Bacillus coagulans to feed can reduce fat accumulation in the liver. Bacillus coagulans supplementation increased the abundance of Firmicutes and decreased the abundance of Actinobacteriota; however, it promoted the proliferation of Lactobacillus and Bacillus, taxa favorable for reducing fat deposition. Additionally, Bacillus coagulans significantly increased ileal bile acid levels of glycochenodeoxycholic acid (GCDCA), tauroursodeoxycholic acid (TUDCA), taurohyodeoxycholic acid (THDCA), lithocholic acid (LCA), and hyodeoxycholic acid (HDCA) and significantly reduced levels of tauro-α-muricholic acid (Tα-MCA). Serum levels of estradiol (E₂), progesterone (P₄), luteinizing hormone (LH), and follicle-stimulating hormone (FSH), as well as the ovarian expression of estrogen receptor alpha (ER-α), FSH receptor (FSHR), and LH receptor (LHR) genes, were significantly increased in the BC group (P＜0.05). Regarding ovarian antioxidant capacity, Bacillus coagulans supplementation significantly up-regulated the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway genes, increased the activities of total superoxide dismutase (T-SOD) and catalase (CAT), and decreased malondialdehyde (MDA) content (P＜0.05). In conclusion, dietary supplementation with Bacillus coagulans improved production performance by regulating hepatic lipid metabolism and enhancing ovarian function in aged laying hens.