Soybean meal (SBM) is rich in functional compounds such as isoflavones, oligosaccharides, and bioactive peptides that can have anti-inflammatory effects. The objective was to assess the impact of increasing SBM, with or without distillers dried grains with solubles (DDGS), on inflammatory biomarkers in grow-finish pigs under commercial conditions. In Exp. 1, a total of 120 pens with 34 pigs per pen (n=4,080 pigs) were used in a 28-d trial with a 2×4 factorial arrangement. Main effects included DDGS (0 or 30%) and increasing SBM (low, low-medium, medium-high, and high) resulting in 15 pens per treatment. Diets formulated without DDGS contained 17.5, 23.3, 29.1, or 34.9% SBM, whereas diets with DDGS included 3.9, 12.8, 21.8, or 30.6% SBM, respectively. After Exp. 1, a washout period from 64 to 84 kg occurred and pigs were fed a common diet with 7.5% DDGS. Following the washout, a total of 3,984 pigs were reassigned to a 2×4 factorial with main effects of DDGS (0 or 15%) and SBM (low, low-medium, medium-high, and high), resulting in 15 pens per treatment with 30 to 34 pigs per pen. Diets with no DDGS contained 6.5, 11.5, 16.4, or 21.3% SBM, while diets with DDGS contained 0, 6.4, 12.8, or 19.2% SBM. On d 28 of each experiment, serum samples were collected via jugular venipuncture from 3 randomly selected pigs per pen. Data were analyzed using a linear mixed model, with pig nested in pen as the experimental unit. Fixed main effects, along with linear and quadratic contrasts for SBM levels, and their interactions with DDGS, were assessed. Serum IL-2, IL-4, IL-12, IL-18, IL1α, IL1β, and IL1ra did not differ among treatments in either experiment (P>0.1). Across both growth phases, increasing SBM levels elevated circulating serum IL-8, independent of DDGS inclusion (linear, P≤0.05). In Exp.1, 30% DDGS inclusion tended to increase serum IL-8 (P=0.086). In Exp.1, regardless of DDGS inclusion, increasing SBM elevated serum IL-10 (linear, P=0.033), but tended to decrease circulating GM-CSF (linear, P=0.061). Addition of 15% DDGS in Exp. 2 decreased serum IL-6 concentrations (P< 0.01). A trend towards an interaction between DDGS and SBM was noted in Exp. 2 for GM-CSF, with high SBM inclusion in diets containing DDGS resulting in increased GM-CSF (P=0.088). In Exp. 2, a linear interaction between DDGS and SBM was observed for IL-10 and TNFα, where increasing SBM in DDGS-free diets lowered circulating IL-10 and TNFα, but this effect was not observed in diets with DDGS (P< 0.05). Collectively, these findings highlight potential immune-modulating effects of increasing soybean meal levels in swine diets under commercial conditions, notably through modulation of IL-8, IL-10, TNFα, and GM-CSF.

Putnam, M., H. Miller, R. Self, P. Giacomini, R. Goodband, J. Woodworth, K. Gaffield, A. Gaines, C. Shull, O. Mendoza and A. Petry. 2025. Assessing inflammatory mediators in commercial grower and finisher pigs fed increasing soybean meal with or without distillers dried grains with solubles. 2025 American Society of Animal Science Midwest Section meeting, Abstract 102.