Effects of Fermented Soybean Hulls on Reproductive Performance, Blood Physiology and Immune Parameters Along with Fecal Microbiota in Sows

This study aims to investigate the effects of fermented soybean hulls (FSHS) on reproductive performance, plasma biochemical profiles, immune parameters, and fecal microbiota in sows. A total of 325 sows were randomized into five groups, each fed a diet with varying FSHS proportions: 0% (control), 2% (FSHS2), 4% (FSHS4), 6% (FSHS6), and 8% (FSHS8). Diets were prepared by replacing conventional soybean hulls with FSHS in equal amounts. The study lasted from day 30 to day 110 of gestation. The results indicated the following: (1) Reproductive Performance: The number of live piglets per litter, newborn litter weight, and individual piglet weight increased linearly with the increase in FSHS addition in the diet (P_Linear < 0.05). A trend toward reduced farrowing duration was observed when FSHS was added to the diet (P_Linear = 0.076). FSHS improved newborn weight and weight variation compared to the control when FSHS was added to the diet (P_Anova < 0.05). Replacing soybean hulls with FSHS also increased fecal scores, enhancing fecal consistency and alleviating constipation (p < 0.01). (2) Plasma Biochemical Indicators: Plasma urea concentration on day 60 decreased linearly with increasing FSHS (P_Linear < 0.05). Plasma total protein and aspartate aminotransferase (AST) activities showed quadratic effects (P_Quadratic < 0.05) on day 60 and 90 of gestation, while alkaline phosphatase activity on day 90 showed a quadratic trend (P_Quadratic = 0.082). (3) Hormone Levels: Plasma insulin and adrenaline levels exhibited quadratic effects on day 60 and 90 of gestation, respectively (P_Quadratic < 0.05). (4) Immune Parameters: Plasma immunoglobulin G (IgG) and M (IgM) levels increased linearly with FSHS proportion on day 60 (P_Linear < 0.05), but no significant changes were observed on day 90 (p > 0.05). (5) Fecal Microbiota: On day 90, the abundance of actinobacteriota increased quadratically with FSHS levels (P_Quadratic < 0.05), while bacteroidota decreased linearly (P_Linear < 0.05). During parturition, actinobacteriota abundance continued to increase linearly (P_Linear < 0.05). Notably, the FSHS8 group had higher actinobacteriota abundance compared to the control group (p = 0.05). At the genus level, terrisporobacter showed a quadratic increase and then decrease (P_Quadratic < 0.05), while ruminococcus showed a quadratic decrease and then increased (P_Quadratic < 0.05). Both terrisporobacter in the FSHS2 and FSHS6 groups and ruminococcus in the FSHS8 group were more abundant compared to the control (p < 0.01). Conclusions: Dietary supplementation with FSHS increased fecal microbial diversity, alleviated the incidence of constipation, and ultimately improved sow reproductive performance. The recommended optimal addition of FSHS to the sow diet is 6%.