Enhancing Immunity and Gut Microbiota Balance with Black Soldier Fly Larvae (BSFL) Meal: A Sustainable Feed Ingredient That Maintains Growth Performance in Pekin Ducks

The effects of substituting soybean meal with black soldier fly larvae (BSFL) meal on the growth performance, immunological response, intestinal morphology, and gut microbiota of Pekin ducks were assessed. A total of 150 one-day-old Pekin ducks were randomly allocated to three isonitrogenous and isocaloric diets: a control diet (0% BSFL), and diets including 10% or 30% BSFL meal (T10 and T30, respectively). Over 42 days, growth metrics, organ indices, serum and jejunal immune parameters, intestinal morphology, and caecal microbiota composition were evaluated. Ducks fed BSFL-containing diets exhibited a significant increase in spleen index compared to the control group (0.06% ± 0.02% for T10 and T30 vs. 0.05% ± 0.01% for control, p < 0.05), while other organ indices and growth performance remained unaffected. Serum levels of immunoglobulins (IgG, IgM, sIgA), cytokines (IFN-γ, IL-2), and complements (C3, C4) were significantly elevated in both BSFL groups (p < 0.05). Jejunal immune indices, including IgG, IgM, IL-2, and C3, were also significantly higher in the T10 group (p < 0.05). Intestinal morphology showed a significantly increased villus-to-crypt ratio in the duodenum and jejunum (p < 0.05). Analysis of gut microbiota indicated that BSFL supplementation was associated with changes in caecal microbial composition, including a lower relative abundance of Proteobacteria. However, alpha diversity indices did not differ significantly among groups. These findings suggest that BSFL meal can replace soybean meal at inclusion levels up to 30% in Pekin duck diets without adversely affecting growth performance, while enhancing select immune parameters and modulating gut microbiota composition.