Early pregnancy diet with sodium butyrate, selenium yeast and soy isoflavones increases sows’ litter size and normal neonatal piglet numbers in association with sex hormones synthesis, antioxidant capacity and gut microbiota

Abstract Embryo loss during the implantation period is one of the main factors limiting litter size in sows. This study aimed to investigate whether combined supplementation with sodium butyrate (SB), selenium yeast (SeY) and soy isoflavones (SIF) during early pregnancy could improve embryo implantation and consequently increase litter size. 103 Landrace × Yorkshire sows of parity 6–7 were randomly allocated into: (1) control group ( n = 56) fed basal diet, and (2) SB-SeY-SIF treatment group ( n = 47) supplemented with 0.05% SB, 50 ppm SeY, and 0.02% SIF in the basal diet from pregnancy days 1–28. Serum and fecal samples were collected on pregnancy day 14 and 28. After farrowing, reproductive performance data were recorded for both groups. SB-SeY-SIF supplementation increased the litter size (17.70 vs. 16.46) and the number of normal neonatal piglets (birth weight > 0.7 kg and without malformations, 14.21 vs. 13.23) ( P < 0.05). Further analyses demonstrated that SB-SeY-SIF enhanced serum estradiol (E2) and progesterone (P4) levels, improved total antioxidant capacity and the activities of key antioxidant enzymes including catalase, superoxide dismutase, glutathione peroxidase and thioredoxin reductase, while reduced malondialdehyde levels ( P < 0.05). Correlation analyses between reproductive performance and differential gut microbiota, and differential serum and fecal metabolites revealed that potential beneficial bacteria (such as Phascolarctobacterium succinatutens ) and metabolites associated with blastocyst development and implantation (such as betaine and Prostaglandin I2) were positively correlated with both litter size and normal neonatal piglet numbers ( P < 0.05). During early pregnancy, the beneficial effects of dietary SB-SeY-SIF supplementation on increasing litter size and the number of normal neonatal piglets were associated with enhanced steroid hormone synthesis, improved antioxidant capacity, and pronounced alterations in the gut microbiota and serum metabolic profiles.