Dietary Astragalus Crude Extract Boosts Piglet Growth and Mitigates Weaning Stress by Enhancing Antioxidant Activity, Improving Immunity, and Modulating Intestinal Microbiota

Astragalus is a traditional Chinese medicine that contains various bioactive compounds, which exert antioxidant and immunomodulatory properties. This research aimed to investigate the impacts of Astragalus crude extract on growth performance, nutrient digestibility, immune response, and intestinal health in weaned piglets. Sixty crossbred weaned piglets at 28 days of age (8.12 ± 0.14 kg) were allocated into three dietary treatments: a control group fed a corn–soybean meal-based diet (CON), an antibiotic group received the basal diet with 1000 mg/kg aureomycin (AN), and a treatment group administered the basal diet with 500 mg/kg Astragalus crude extract (CE), with 5 replicates per group, 4 piglets per replicate. The experimental trial lasted for 28 days. Feed intake and body weight were recorded to evaluate growth performance. Blood, intestine, and liver tissue samples were collected for the analysis of antioxidant capacity and gene expression. Compared to the CON group, supplementation with CE or AN significantly enhanced growth performance and decreased diarrhea incidence on days 0–14, whereas only CE tended to improve crude protein digestibility. Piglets supplemented with AN or CE showed improved antioxidant capacity and immune response relative to the CON group, as evidenced by increased liver and intestinal antioxidant enzyme activities, upregulated intestinal antioxidant gene expression, and enhanced plasma immunoglobulin A levels. Further, the upregulated intestinal tight junction protein expression was observed in CE or AN groups compared with the CON. Notably, dietary CE significantly modulated gut microbiota composition, particularly enriching the genera Blautia, Turicibacter, Agathobacter, and Clostridium. These findings indicate that dietary Astragalus crude extract promotes the gut health of weaned piglets by reducing oxidative stress and modulating gut microbiota composition, thereby decreasing diarrhea incidence and improving growth performance.