Dietary Supplementation with Protocatechuic Acid and a Complex Eucommia ulmoides Leaf Extract Differentially Enhanced Reproductive Performance and Modulated Gut Microbiota in Late-Pregnancy Sows

Nutrition during late pregnancy plays a critical role in fetal development. This study was conducted to investigate the effects and underlying mechanisms of protocatechuic acid (PCA) and PCA-rich <i>Eucommia ulmoides</i> leaf extract (EU) on reproductive performance using late-pregnancy sows as a model. A total of 30 sows (Landrace × Yorkshire; average parity: 3-4) with similar body condition (assessed as a score of 4 on a 5-point scale) were randomly assigned to three treatments (<i>n</i> = 10 per group) from day 80 of gestation until farrowing and fed either a basal diet, a basal diet supplemented with 200 g/t of PCA, or 1000 g/t of EU. Results demonstrated that dietary supplementation with PCA and EU, which delivered a negligible amount of PCA but contained other bioactive phytochemicals such as chlorogenic acid, significantly increased litter weight at birth and the number of healthy piglets (<i>p</i> < 0.05), along with elevated levels of colostral immunoglobulins and reduced serum interleukin (IL)-6 concentrations (<i>p</i> < 0.05). Furthermore, PCA supplementation was associated with a decrease in fasting glucose levels and improved insulin sensitivity (<i>p</i> < 0.05), accompanied by an increased relative abundance of Bacteroidetes (<i>p</i> < 0.05). Analysis of gut microbial composition revealed that both PCA and EU reduced the relative abundance of <i>Paraprevotella</i> (<i>p</i> < 0.05), while PCA increased the abundance of the <i>dgA11_gut_group</i> (<i>p</i> < 0.05), and EU enriched <i>Caldicoprobacter</i> (<i>p</i> < 0.05). Correlation analysis indicated that PCA- and EU-modulated genera, such as <i>Lysinibacillus</i>, were positively associated with colostrum lactose and colostrum fat but negatively correlated with the number of somatic cells, colostrum protein, degreased dry matter, total solids, and urea nitrogen (<i>p</i> < 0.05). In conclusion, dietary supplementation with PCA and EU differentially enhanced reproductive performance and colostrum immunoglobulins, at least partially, through the modulation of inflammation and glucose metabolism-related gut microbiota in late-pregnancy sows.