Comparative Effects of Processed Soybean Protein Sources on Growth, Serum Immune and Endocrine Profiles, and Colonic Microbiota in Weaned Piglets

Weaning stress and antinutritional components in conventional soybean meal may impair intestinal homeostasis and growth in nursery piglets. This study compared five soybean protein sources: conventional soybean meal (SBM), rapidly expanded soybean meal (RSB), fermented soybean meal (FSBM), hydrolyzed soybean protein (HP), and extruded full-fat soybean (ESB). Two concurrent 28-day trials used 120 newly weaned piglets, with 60 piglets per trial allocated to five treatments (six pens per treatment and two piglets per pen): a single-diet trial and a dual-choice feed-preference trial. Growth, feed preference, crude protein digestibility, serum biomarkers, and colonic microbiota were evaluated. HP showed the highest in vitro and apparent crude protein digestibility and increased final body weight and average daily gain relative to SBM and RSB (p < 0.05). Compared with SBM, HP increased serum IgA, IL-2, GH, and IGF-1 and decreased TNF-α (p < 0.05). Serum antioxidant indices and microbial alpha diversity did not differ among treatments (p > 0.05). Descriptive genus-level analyses indicated a higher relative abundance of Lactobacillus in the HP and FSBM groups. Overall, HP produced the most consistent improvements in protein digestibility and selected growth and serum outcomes under the conditions of this study.