Oral administration of ultrafine-grained Astragalus membranaceus enhances peripheral immunity in weaned black Xiangdong goats by upregulating the complement regulator C4bp and immunoglobulin responses.

Astragalus membranaceus is a widely used immunomodulatory herb in traditional Chinese medicine; however, the effects of its ultrafine-grained powder (UGAM) on the peripheral immune system of young ruminants remain largely unexplored. Thirty-six weaned black Xiangdong goats (postnatal day 42; 5.34 ± 1.342 kg) were randomly allocated to a control group (n = 16; basal diet only) and a UGAM group (n = 20; control plus 10 g/d UGAM) from postnatal days 43-78, including 8 days adaption period. On postnatal day 78, blood samples were analyzed for complement proteins (C1q, C1r, C1s, C3, C4, C4bp, and Factor H), immunoglobulins (IgA, IgG, and IgM), and inflammatory cytokines (IL-1α, IL-1β, IL-6, IL-10, TNF-α, and IFN-γ), along with peripheral blood cell profiles. Hepatic complement gene expression was measured in a randomly selected subset of animals (Control n = 11; UGAM n = 16) using RT-qPCR. UGAM significantly increased serum C4bp concentrations and serum and hepatic C4bp mRNA expression (p < 0.001) and increased peripheral IgM concentrations (p = 0.032), whereas IgA, IgG, and all measured inflammatory cytokines (IL-1α, IL-1β, IL-6, IL-10, TNF-α, and IFN-γ) remained unchanged (p > 0.05). In the multi-parameter analysis, UGAM treatment was independently and positively associated with C4bp (partial r = 0.74, p < 0.001), and the overall correlation structure of the complement system was positively associated with that of the immunoglobulins (Mantel r = 0.36, p = 0.001). Oral administration of UGAM increased circulating C4bp and IgM and hepatic C4bp in weaned goats, consistent with engagement of homeostatic complement regulatary and possible post-weaning immune support. However, complement activity, plasma-cell responses, signaling, and safety were not measured; mechanisms remain hypothetical and require validation.