Abstract
The gut-ovary axis involves a complex interplay of various physiological and molecular mechanisms, which significantly impact poultry production and health. This study investigated the effects of betaine (Bet) on the gut-ovary axis of laying hens in aged laying hens. A total of 108 Hy-Line Brown hens, aged 500 days, were randomly divided into three groups (n = 36 per group) and fed diets containing 0, 1000, and 3000 mg/kg of Bet (designated as CON, l-Bet, and H-Bet, respectively) over a 42-day trial. The results indicated that dietary supplementation with Bet improved laying performance. Specifically, H-Bet Supplementation increased villus height (VH) and villus height/crypt depth ratio (VH/CD), and up-regulated the expression of Claudin-1 in the jejunal and ileal mucosa. Additionally, H-Bet enhanced the richness of Bacteroidetes and reduced Firmicutes/Bacterodietes ratio. LEfSe analysis revealed significant enrichment Eubacteriaceae, Merdibacter, Anaerorhabdus_furcosa_group, Syntrophococcus, and Clostridium_innocuum_group in Bet group. Transcriptome sequencing of small yellow follicles (SYFs) showed significant up-regulation of ATP6 and down-regulation of EGR1. KEGG enrichment analysis indicated that H-Bet influenced oxidative phosphorylation, peroxisome, and other pathways, with GESA was primarily enriched in oxidative phosphorylation, and MAPK signaling pathway. Furthermore, H-Bet supplementation increased SOD, CAT, Nrf2, NQO-1, and HO-1 expression in the jejunum, while only HO-1 expression was up-regulated in the ileum. In the ovary, H-Bet differentially affected GPX, and CAT expression. These results demonstrate that dietary supplementation with Bet improves intestinal and ovarian health in aged laying hens, likely due to enhanced antioxidant capacity and improved intestinal morphology.