Four experiments were conducted to determine the effects of increasing soybean meal (SBM) in diets with or without 25% DDGS on growth performance of nursery pigs. Treatments were arranged in a 2 × 3 factorial with main effects of SBM (27.5, 32.5, or 37.5%) and DDGS (0 or 25%). A total of 296, 2,502, 4,118, and 711 pigs, initially 10.6, 11.7, 12.5, and 12.3 kg, were used and there were 10, 16, 13, and 12 replicates per treatment in Exp. 1, 2, 3, and 4, respectively. Experimental diets were fed for 21 d. Pigs were weighed and feed disappearance measured to calculate ADG, ADFI, G:F, and caloric efficiency (CE). Data were analyzed using the GLIMMIX procedure of SAS with block as random effect and treatment as fixed effect. The average cull rate was 0.7, 0.5, 0.2, and 0% and the mortality rate was 0.7, 0.3, 0.4, and 0% in Exp. 1 to 4, respectively. There were interactions (P ≤ 0.039) between SBM and DDGS for G:F and CE in Exp. 2 and for ADG and ADFI in Exp. 3. These were mostly driven by increasing SBM negatively affecting performance in a greater magnitude when diets contained DDGS compared to diets without DDGS. The main effects of DDGS and SBM were more consistent across experiments. Pigs fed diets with 25% DDGS had decreased (P ≤ 0.001) ADG and ADFI in all experiments as well as poorer (P ≤ 0.028) G:F and CE except for Exp. 3.
Feeding increasing amounts of SBM generally did not result in any major impact in ADG, but consistently improved (linear, P ≤ 0.078) G:F and CE across experiments. The mechanism for this response is unclear but could be driven by intrinsic components of SBM or underestimating the energy value of SBM.