Dietary supplementation with selenium yeast during early pregnancy enhances litter size in association with antioxidant capacity, progesterone synthesis, and gut microbiota in sows

Early embryonic implantation quality is a key determinant of litter performance in sows. Selenium plays a vital role in maintaining optimal female reproductive performance. This study aims to assess the impact of selenium yeast supplementation during early pregnancy on embryo implantation efficiency and litter size in sows. This trial involved multiparous Landrace × Yorkshire (L × Y) crossbred sows. The control group ( n = 45) was fed a basal diet. The selenium yeast group ( n = 43) was supplemented with selenium yeast from 7 days before mating through gestation day 21. The results showed that selenium yeast supplementation significantly increased litter size ( P < 0.05). Selenium yeast supplementation significantly increased serum progesterone and enhanced antioxidant capacity, as evidenced by elevated serum glutathione peroxidase, superoxide dismutase, and catalase activities, along with reduced malondialdehyde activity ( P < 0.05). 16S rRNA gene sequencing and untargeted metabolomic analysis revealed that supplementation with selenium yeast significantly increased the abundances of Lactobacillus amylovorus ( L. amylovorus ), Limosilactobacillus reuteri ( L. reuteri ), and Lactobacillus johnsonii ( L. johnsonii ), as well as the butyric acid levels ( P < 0.05). Correlation analysis indicated that butyric acid levels were significantly and positively correlated with litter size and healthy litter size ( P < 0.05). In sum, the increase in litter size resulting from selenium yeast supplementation during early pregnancy is associated with improved maternal antioxidant defenses, enhanced progesterone production, modulation of gut microbiota composition, and alterations in metabolic profiles in sows. IMPORTANCE This study demonstrated that selenium yeast supplementation during early pregnancy plays a critical role in reproductive performance. It improves embryo implantation quality and increases litter size. Systematic evaluation of selenium yeast supplementation revealed that it significantly enhances maternal antioxidant capacity and progesterone concentrations. Furthermore, it promotes the enrichment of beneficial Lactobacillus species and increases butyric acid levels. Further analysis revealed that butyric acid levels were significantly positively correlated with litter size and healthy litter size, suggesting that Lactobacillus amylovorus , Limosilactobacillus reuteri , Lactobacillus johnsonii , and butyric acid may be potential probiotics and metabolites regulating litter size in sows. The study provides scientific evidence that precision nutrition strategies can improve sow reproductive performance and herd productivity. It also holds significant practical value for sow health management and the swine industry.