Dietary Astragalus and Fermented Astragalus in Postpartum Turpan Black Ewes: Impacts on Maternal Health, Rumen Microbiota, Lactation, and Lamb Development

Raw and fermented Astragalus membranaceus (AM) serve promising herbal additives for small ruminants, yet their integrated regulatory functions across lactating ewes and suckling lambs are insufficiently characterized. This study aimed to elucidate how dietary supplementation with raw and fermented Astragalus membranaceus modulates ruminal microbial communities, circulating metabolites, redox homeostasis, and lactation performance in postpartum Turpan black ewes, and to characterize the consequent effects on immune development and body weight gain in their offspring. The findings are intended to inform evidence-based strategies for herbal supplementation in sheep production. Forty-five postpartum Turpan black ewes were randomly allocated to three groups (n = 15): control (basal diet), AM and FAM groups. Ewe plasma, rumen fluid, milk yield, milk composition and serum antioxidant indices were sampled periodically. Lamb body weight, plasma antioxidants, immunoglobulins, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) were measured every 15 days. Rumen 16S rRNA sequencing and untargeted plasma metabolomics were performed on day 45 post-partum. The group of FAM significantly increased milk yield (p < 0.05) and markedly improved total antioxidant capacity in ewes (p < 0.01). In the AM group, metabolites such as linoleic acid were significantly downregulated (p < 0.05), with enrichment in the linoleic acid metabolism pathway, while flavonoid metabolites, including quercetin 4′-isobutyrate, were strongly upregulated (p < 0.01). In the FAM group, tetradecanoic acid, palmitoleic acid, and related metabolites were significantly reduced (p < 0.05), and these differential metabolites showed significant enrichment in fatty acid biosynthesis (p < 0.05). Flavonoid compounds represented by melilotocarpan E were also significantly upregulated (p < 0.05). Rumen microbial diversity was significantly higher in the FAM group (p < 0.05). At the genus level, the FAM group showed enrichment of fiber-degrading bacteria, including Rikenellaceae_RC9_gut_group, unclassified_Muribaculaceae, and unclassified_F082. In newborn lambs, plasma GH and IGF-1 levels increased markedly in both the FAM and AM groups (p < 0.01). In the FAM group, immunoglobulin A (IgA) and immunoglobulin G (IgG) concentrations were also markedly elevated (p < 0.01). In addition, lambs in the FAM group exhibited substantially higher plasma catalase (CAT) activity and nitric oxide (NO) concentration (p < 0.01), whereas plasma total antioxidant capacity was significantly lower (p < 0.01). In conclusion, AM and FAM supplementation increased the relative abundance of Bacteroidetes, regulated fatty acid synthesis through modulation of plasma metabolites, enhanced antioxidant capacity in ewes, increased milk fat percentage, and improved immune function, antioxidant status, and growth performance in lambs. To provide a theoretical basis and data support for its application in ewes after lambing and for improving the growth and development of lambs. Overall, FAM produced superior effect.