Bacillus coagulans Improves Performance by Modulating Bile Acid Metabolism to Suppress Hepatic Lipid Accumulation and Attenuating Ovarian Oxidative Stress in Late Laying Hens

In the late laying phase, 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. The experiment involved 180 Hy-Line Grey laying hens (65 weeks of age) with similar initial egg production rates. The aged hens were randomly assigned to two treatments with six replicates of 15 hens each. A one-way experimental design was employed: CON group (basal diet) and BC group (basal diet supplemented with 3 × 109 CFU/kg of Bacillus coagulans). The research found that adding Bacillus coagulans to feed significantly reduces ADFI and the feed-to-egg ratio, whilst increasing egg production (p < 0.05). Bacillus coagulans supplementation increased the abundance of Firmicutes and decreased the abundance of Actinobacteriota (p < 0.05), while promoting the proliferation of Lactobacillus and Bacillus (p < 0.05). Furthermore, Bacillus coagulans significantly increased the levels of the bile acids GCDCA, TUDCA, THDCA, LCA, and HDCA in the ileum (p < 0.05). Bacillus coagulans not only increased the activity of T-SOD and CAT in the ovaries, as well as the expression of the Nrf2, HO-1, and SOD1 genes (p < 0.05), but also increased the expression of the estrogen receptor ER-α, FSHR and LHR genes (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.