Effect of heating, microbial fermentation, and enzymatic hydrolysis of soybean meal on growth performance, nutrient digestibility, and intestinal microbiota of weaned piglets

The macromolecular proteins, anti-nutritional factors, and allergens contained in soybean meal (SBM) have a negative impact on the growth of weaned piglets. The objective of this study was to investigate the effects of heating, microbial fermentation, and enzymatically hydrolyzed SBM on the growth performance, nutrient digestibility, serum biochemistry, intestinal morphology, volatile fatty acids, and microbiota of weaned piglets. After the preparation of soaked SBM (SSBM), enzymatically hydrolyzed SBM (ESBM), and microbial fermented and enzymatically hydrolyzed SBM (MESBM), 72 weaned piglets were randomly allocated to three groups for a 21-d trial. In the three groups, 17% of conventional SBM in basal corn-soybean meal diet was replaced by an equivalent amount of SSBM (control group), ESBM, or MESBM. The results showed that the contents of glycinin, beta-conglycinin, trypsin inhibitor, and proteins above 20 kDa were significantly decreased in ESBM and MESBM, compared with SSBM, and the surface of ESBM and MESBM had more pores and fragmented structure. In the second week and throughout the entire experimental period, the diarrhea index was reduced (P < 0.01) in ESBM and MESBM in contrast with SSBM. Furthermore, the inclusion of ESBM and MESBM in the diet improved the apparent total tract digestibility of dry matter and crude protein (P < 0.05), and increased the abundances of the genera Lactobacillus and Clostridium_sensu_stricto_1, respectively. Metagenomic sequencing further identified that members of six species of Proteobacteria, four species of Clostridiales, and three species of Negativiautes were enriched in the colon of piglets fed MESBM, while two bacterial species, Lachnoclostridium and Lactobacillus_points, were enriched in the colon of piglets fed ESBM. In conclusion, replacing SSBM with ESBM or MESBM in the diet decreased the diarrhea index, which could be associated with improved nutrient digestibility and microbial composition.