Increasing dietary soybean trypsin inhibitor protein attenuates nursery pig performance

Authors: MILLER, KAYLA - Iowa State University; SPENCER, JOEL - United Animal Health; Krishnan, Hari; MENDOZA, OMARH - Maschhoff Pork Farm; MCCALLUM, MICHELLE - United Animal Health; MAHONEY, JULIE - United Animal Health; BURROUGH, ERIC - Iowa State University; GABLER, NICHOLAS - Iowa State University

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2025
Publication Date: 7/11/2025
Citation: Miller, K.A., Spencer, J.D., Krishnan, H.B., Mendoza, O.F., Mccallum, M.N., Mahoney, J.A., Burrough, E.R., Gabler, N.K. 2025. Increasing dietary soybean trypsin inhibitor protein attenuates nursery pig performance. Translational Animal Science. 9. https://doi.org/10.1093/tas/txaf089.
DOI: https://doi.org/10.1093/tas/txaf089

Interpretive Summary: Soybean meal is the most used protein source in animal diets due to its excellent nutritional quality, wide availability, and relatively low cost. However, soybeans contain anti-nutritional factors that can hinder pig growth if not properly heated. Trypsin inhibitor proteins, inherent to soybeans and soy products, pose a significant challenge in swine diets. Few studies have systematically examined dietary active trypsin inhibitor concentrations on nursery pig performance. Understanding the impact of trypsin inhibitor content in soybeans is crucial for increasing soybean meal (SBM) inclusion in animal feed. This study aimed to evaluate the effects of dietary active trypsin inhibitor concentrations on nursery pig performance, fecal consistency, and intestinal health metrics. Five diets with increasing trypsin inhibitor concentrations were formulated utilizing soybean flour. Our study showed that the growth performance metrics of nursery pigs, including daily weight gain, feed intake, and feed efficiency, declined at concentrations exceeding 1.22 TIU per mg of complete feed. These findings provide valuable insights into the practical use of soy-based proteins in early nursery pig diets. Our findings will benefit U.S. farmers by encouraging the broader use of SBM in the animal industry and potentially leading to the inclusion of full-fat soybeans in nursery pig diets.

Technical Abstract: Trypsin inhibitor proteins are antinutritional compounds innate to soybeans that reduce protein digestibility, amino acid bioavailability, and growth performance of pigs. The objective of this study was to evaluate the impact of increasing levels of dietary trypsin inhibitor unit activity (TIU/mg) on nursery pig growth performance and health. In a 41-d study, 1,140 newly weaned nursery pigs (5.9 ± 0.34 kg BW) were allotted into split sex pens, blocked by body weight, assigned randomly to one of five dietary treatments (n = 19 pens/treatment) varying in TIU/mg concentration, and fed over three dietary phases. Treatments targeted 0.41, 1.32, 2.20, 3.08, and 3.96 TIU/mg of complete feed averaged over the three phases and were achieved by using a corn-soybean meal basal diet with added soybean flour. Analyzed dietary treatments averaged 0.61, 1.22, 2.19, 3.41, and 3.51 TIU/mg. Pen BW and feed disappearance were recorded at the start and end of each phase to calculate ADG, ADFI, and G:F. Fecal consistency was scored and recorded daily. On d 21 of the study, 10 pigs per treatment were sacrificed for intestinal sample collection. Data were analyzed with pen as the experimental unit, the random effect of block, and the fixed effect of TIU, including polynomial contrasts for linear and quadratic effects of 0.61 to 3.51 TIU/mg treatments. No quadratic responses to dietary TIU/mg activity were reported in any parameters. Overall, as active dietary TIU/mg increased, ADG, ADFI, and G:F linearly decreased (P < 0.001). Pigs fed the highest level (3.51 TIU/mg) exhibited reduced ADG by 25%, ADFI by 17%, and G:F by 8% compared to pigs fed the lowest level (0.61 TIU/mg). Dietary TIU/mg did not affect fecal consistency, mortality, or removals (P > 0.10). Individual and total concentrations of colonic biogenic amines and short chain fatty acids did not differ (P > 0.10). Histological lesions of the ileum and colon did not differ (P > 0.10). Ileum VH tended to decrease (P = 0.078) and CD linearly decreased as TIU/mg increased (P = 0.004), but VH:CD and colonic CD were similar (P > 0.10). Moderate relationships between TIU intake and G:F (R2 = 0.393), caloric efficiency (R2 = 0.378), and lysine efficiency (R2 = 0.376) were observed. In conclusion, soybean-derived active TIU concentrations negatively impact nursery pig performance above 1.22 TIU/mg, with minimal impacts on intestinal and pig health.