Dietary soybean-derived trypsin inhibitor protein reduces nursery pig performance and may exacerbate F18 enterotoxigenic Escherichia coli disease

Authors: NISLEY, MITCHELL - Iowa State University; BURROUGH, ERIC - Iowa State University; SPENCER, JOEL - United Animal Health; MENDOZA, OMARH - Maschhoff Pork Farm; Krishnan, Hari; GABLER, NICHOLAS - Iowa State University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2026
Publication Date: 2/5/2026
Citation: Nisley, M.J., Burrough, E.R., Spencer, J.D., Mendoza, O.F., Krishnan, H.B., Gabler, N.K. 2026. Dietary soybean-derived trypsin inhibitor protein reduces nursery pig performance and may exacerbate F18 enterotoxigenic Escherichia coli disease. Journal of Animal Science. 104. https://doi.org/10.1093/jas/skag026.
DOI: https://doi.org/10.1093/jas/skag026

Interpretive Summary: Soybean meal is the primary protein source in animal diets due to its quality, availability, and cost. However, trypsin inhibitors in soy can impair pig growth by increasing foregut and hindgut fermentation, leading to diarrhea. One common bacterium that causes diarrhea in young pigs after weaning is E. coli (specifically the F18 type). Yet, few studies have examined its interaction with dietary trypsin inhibitors. In this study, we examined that interaction in detail. Our study found that pigs fed diets with more than 2.4 trypsin inhibitor units required more antibiotics and had higher mortality under E. coli challenge, while diets with 4.2 units impaired growth. Overall, high trypsin inhibitor levels worsened E. coli-related morbidity and reduced performance. These results emphasize the need for U.S. swine producers to monitor trypsin inhibitor concentrations in soybean-based feeds to limit the impact of harmful bacteria.

Technical Abstract: Soybean-derived trypsin inhibitor proteins (TIU) impair amino acid bioavailability and increase exogenous and endogenous nitrogen flow to the hindgut, thereby attenuating pig growth performance. High-protein diets potentiate proteolytic fermentation-induced alterations to the gut microbiome, which may increase opportunistic enterotoxigenic Escherichia coli (ETEC) proliferation and exacerbate disease. We hypothesized that feeding high-TIU diets to nursery pigs would reduce growth rates and exacerbate F18 ETEC disease. Two hundred and eighty-eight (5.42 ± 0.93 kg BW; Camborough 1050 × 337, [PIC, Hendersonville, TN]) newly weaned pigs were evenly allotted across two control rooms (CON) and two challenge rooms (ETEC). Pigs were allotted based on sex and a-(1,2) fucosyltransferase (FUT1) genotype, with both factors evenly distributed across all pens. Pens were randomly assigned to corn-soy diets consisting of 1.1, 2.4, or 4.2 TIU/mg, creating six treatments: CON1.1, CON2.4, CON4.2, ETEC1.1, ETEC2.4, and ETEC4.2 (8 pens/treatment). On day 10 (day post-infection [dpi] 0), pigs in the ETEC rooms were orally inoculated with 5 mL of 3.8 × 109 cfu/mL of an F18 ETEC culture. Pooled pen feces were assessed for dry matter (DM) on dpi 0, 3, 5, 7, 9, 11, 14, and 21. Pen growth performance, medical treatments, and mortality were assessed prior to infection (dpi -10 to 0) and post infection (dpi 0 to 28). On dpi 5 and 12, one pig/pen was sacrificed to assess ileal mucosal attachment of F18 ETEC via in situ hybridization. Pen was the experimental unit and data were analyzed for the interactive and main effects of diet and challenge. Increasing dietary TIU to 4.2 TIU/mg led to a 13–16% decrease in ADG compared to the 1.1 TIU/mg diets, regardless of the challenge (P = 0.014). A diet × challenge interaction was observed regarding mortality, with ETEC2.4 showing a 20.8% mortality rate compared to 0% in CON2.4 (P = 0.001). Similarly, 22.9% of ETEC2.4 pigs required antibiotic treatment compared with 0% of CON2.4 pigs (P = 0.001). Fecal DM from dpi 0–21 showed no interaction, but ETEC pens had lower fecal DM compared to CON pens from dpi 3–11 (P<0.0001). On dpi 5, ileal F18 attachment was increased in ETEC versus CON pigs (3.7 × 10-3 vs 0.1 × 10-3 F18 copies/µm2, P<0.0001). By dpi 12, ileal F18 attachment did not differ between challenge groups (P>0.05), suggesting disease resolution. In conclusion, diets at or greater than 2.4 TIU/mg decreased pig growth and reduced livability in ETEC-infected nursery pigs.