Water-soluble fiber can act as a substrate for intestinal microbiota to synthesize short-chain fatty acids (SCFA), providing energy to intestinal cells and modulating immune responses by regulating cytokine production. This 42-d study investigated the effects of standard soybean meal (SSBM, 464 g/kg crude protein) or low-protein SBM (LPSBM) on inflammatory cytokine gene expression in spleen and cecal tonsils (CT), CD8+:CD4+ cell ratio, jejunal tissue histomorphology in broiler chickens challenged with mixed Eimeria spp. Three LPSBM were produced by adding soyhull (SH) to SSBM at 27, 55, or 86 g/kg rates to produce LPSBM1, 2, and 3, with 449, 437, and 417 g/kg crude protein, respectively. 1,056 male broilers were allocated to eight treatments in a 4 x 2 factorial arrangement, consisting of four corn-based diets with challenge (CH) or without challenge (NCH). All diets were balanced for metabolizable energy, crude protein, and standardized digestible amino acids. Challenge with mixed Eimeria spp was done on d 14. Spleen and cecal tonsils were collected on d21 and d28 to assess immunological responses, and jejunal tissue was collected on d21 to assess villus height (VH), crypt depth (CD), and VH:CD ratio. The data were analyzed by two-way ANOVA in a 4×2 factorial arrangement using JMP Pro 17.There were significant Eimeria × diet (P<0.05) interactions where birds in the NCH group fed LPSBM2 had greater VH:CD ratio than the birds in the CH groups. Significant Eimeria × diet (P<0.001) interactions were observed for CT IFN-γ mRNA on d21 and d28 and for IL-1 on d21. Birds in the CH group fed LPSBM diets had decreased expression of these genes compared to birds in SPSBM diets. A diet effect was observed on d21 in CT where birds fed LPSBM2 had lower (P<0.05) CD8+:CD4+ cells than LPSBM1 diet. Bile IgA was significantly higher (P<0.05) in CH birds fed SPSBM than LPSBM3. There were no significant interaction effects on inflammatory cytokines in spleen on d21 and d28. The LPSBM3 decreased (P<0.05) IFN-γ concentration in spleen on d21 compared to LPSBM1 and on d28 there was a tendency (P= 0.064) where SPSBM had higher concentrations than LPSBM1. In conclusion, the inclusion of fermentable fiber in the diet during infection period decreased the proinflammatory cytokines concentration, likely due to the fiber anti- inflammatory properties. These findings suggest that LPSBM diets may help mitigate excessive immune activation during Eimeria challenge while modulating gut health and immune response.

Kasireddy, B. I. Oluseyifunmi, R. Shanmugasundaram,  A. Oladeinde and O. Olukosi. 2025. The effect of low-protein soybean meal with graded inclusion levels of soyhull on immune parameters, jejunal tissue histomorphology in broiler chickens challenged with mixed Eimeria spp. 2025 Poultry Science Association Annual Meeting, Abstract 100