Effects of processed soybean meal on growth performance and gut microbiome composition in pigs in regular nursery and enterotoxigenic <i>Escherichia coli</i> challenged conditions

Hydrothermal-mechanical (HTM) processing of soybean meal (SBM) has been shown to enhance intestinal health and growth in post-weaning pig compared to conventional SBM. It was hypothesized that HTM processing improves protein utilization, particularly under enterotoxigenic <i>Escherichia coli</i> (ETEC) challenge, resulting in better growth and a more resilient hindgut microbiome. A total of 268 weaned pigs (6.82 ± 0.85 kg body weight) were allotted to regular nursery (5 pigs/pen, 10-11 pens/treatment) or ETEC challenge (3 pigs/pen, 12 pens/treatment) and fed one of three isocaloric diets with equal standardized ileal digestible lysine: SBM, HTM SBM, or enzyme-treated (Enz Trt) SBM. Test soy products replaced SBM in a wheat-barley-SBM base diet for the first 3 wk, followed by a common diet for 3 wk. On d 14 post-weaning, ileal digesta and feces were collected for crude protein (CP) digestibility, short-chain fatty acid (SCFA), and microbiome analysis. Growth performance, digestibility, and SCFA data were analyzed using general linear models and microbiome data from Nanopore shotgun sequencing were center-log-ratio transformed for statistical analysis in R. No diet × challenge interaction was observed on ADG, ADFI or BW. Pigs in regular nursery conditions had higher ADG (<i>P < </i>0.01) and ADFI (<i>P < </i>0.05) than ETEC challenged pigs during d 0-7. HTM SBM and Enz Trt SBM improved ADG (<i>P < </i>0.05) with similar ADFI compared to SBM across conditions. From d 7-12, pigs fed HTM SBM or Enz Trt SBM had greater ADG (<i>P < </i>0.05) and ADFI (<i>P < </i>0.01) than SBM-fed pigs. BW remained lower (<i>P < </i>0.05) in SBM-fed pigs from d 12-21 and during the final 3 wk. Under regular nursery conditions, HTM SBM improved apparent total tract digestibility of CP (<i>P < </i>0.01) compared SBM, but with no difference from Enz Trt SBM. Microbiome composition was affected by diet (<i>P < </i>0.01) and ETEC challenge (<i>P < </i>0.01). HTM SBM and Enz Trt SBM tended to increase α-diversity (<i>P = </i>0.10) of the microbiome compared to SBM, with no difference between the two treatments. HTM SBM and Enz Trt SBM increased abundance of species positively correlated with growth and beneficial SCFA, such as caproate (<i>P < </i>0.05) and valerate (<i>P < </i>0.05). In conclusion, HTM SBM and Enz Trt improved ADFI, ADG resulting higher BW and promoted beneficial microbes linked to performance in nursery pigs under both regular nursery and ETEC-challenged conditions.