ABSTRACT: The objective of this experiment was to determine the impact of diets containing increasing amounts of enzymatically treated soybean meal (ESBM) but decreasing amounts of soybean meal (SBM) on growth performance, intestinal structure, and barrier integrity, inflammation, and oxidative status in weaned pigs. A total of 480 pigs [6.3 ± 1.2 kg body weight (BW)] were blocked by initial BW and pens (n = 12 per treatment) were randomly allotted to one of four dietary treatments. Diets were fed in three phases (days 0-14, 14-28, and 28-35) over a 35-d period. The four dietary treatments consisted of a negative control diet (NC): the NC with 7.0% ESBM (ESBM1), the NC with 14.0% ESBM (ESBM2), and the NC with 21.0% ESBM (ESBM3). Soybean meal was reduced proportionately in each treatment. In phase 2, ESBM inclusion was decreased by 50% (3.5%, 7.0%, and 10.5% ESBM, respectively); phase 3 was a common diet and contained no ESBM. Fecal score was visually ranked weekly using a four-point scale. Intestinal tissue, digesta, and blood samples were collected from 48 pigs (1 per pen) on day 10. Data were analyzed using PROC MIXED of SAS (9.4) with pen as the experimental unit; diet and block were considered fixed effects. Linear and quadratic contrasts were used to determine the effect of increasing ESBM. Overall, ESBM2 and ESBM3 decreased final BW, average daily gain, and average daily feed intake compared to NC and ESBM1 (diet, P < 0.05; linear, P < 0.05). Overall fecal score (diet, P < 0.05) and fecal dry matter (P < 0.05) were improved by feeding ESBM diets compared to NC. Volatile fatty acid (VFA) concentration of acetate, propionate, butyrate, and total VFA in ileal contents increased as ESBM inclusion increased (P < 0.05). Colonic VFA concentration was not impacted (P > 0.10). Total antioxidant capacity was increased by ESBM (P < 0.05). The concentration of mucosal interleukin-4 increased as the inclusion of ESBM increased (linear, P < 0.05). Messenger ribonucleic acid abundance of occludin and zonula-occludens-1 in ileal tissue was increased by ESBM1 or ESBM2 (P < 0.05). In conclusion, increasing the dietary levels of ESBM over 7% had a negative impact on nursery pig performance, but ESBM positively impacted fecal score. Feeding ESBM improved oxidative status and intestinal barrier integrity while increasing ileal VFA production but had minimal impact on intestinal inflammation or morphology. Further research is needed to determine the optimal inclusion level of ESBM.
