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ARS Home » Midwest Area » Columbia, Missouri » Plant Genetics Research » Research » Publications at this Location » Publication #436057
Research Project: Redesigning Soybeans for a Resilient Future of Food, Feeds, and Bio-Industry

Location: Plant Genetics Research

Title: Effects of increasing trypsin inhibitor on nursery pig growth performance, fecal dry matter, and nutrient digestibility

Author
item COLLIER, SIERRA - Kansas State University
item SOPER, PAIGE - Kansas State University
item GAFFIELD, KATELYN - Kansas State University
item GOODBAND, ROBERT - Kansas State University
item TOKACH, MIKE - Kansas State University
item WOODWORTH, JASON - Kansas State University
item DEROUCHEY, JOEL - Kansas State University
item Krishnan, Hari
item GEBHARDT, JORDAN - Kansas State University

Submitted to: Translational Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soybean meal (SBM) is the main plant-based protein used in pig diets because it has a good balance of amino acids, is easy for pigs to digest, and is reliably available worldwide. However, SBM also contains natural antinutritional factors (ANFs), including trypsin inhibitors, which bind to the pig’s digestive enzymes and reduce how well pigs can use dietary protein. Because trypsin inhibitor levels (TIU) vary widely in U.S. soybean meal, it’s important to understand how these differences affect young pigs. In this study, we tested how increasing TIU levels influenced nursery pig growth, fecal dry matter, nutrient digestibility, and the level of a specific digestion hormone. We found that higher TIU consistently reduced growth and nutrient digestibility, and even moderate increases led to lighter pigs. These results show why monitoring TIU in soybean meal is essential, helping U.S. swine nutritionists choose the right soybean meal source and inclusion rate to support healthy growth in nursery pigs.

Technical Abstract: A total of 360 barrows (DNA 200 × 400; initially 6.1 ± 0.03'kg) were used in a 42-d growth trial to evaluate the effects of increasing trypsin inhibitor units (TIU) in complete feed on nursery pig growth performance, fecal dry matter (DM), and nutrient digestibility. At weaning, pigs were blocked by BW and randomly assigned to pens with five pigs per pen and 12 pens per treatment. There were six dietary treatments formulated to provide 1.4, 2.1, 2.8, 3.5, 4.2, and 4.9 TIU/mg of complete feed. Soy flour (76 TIU/mg) was added at the expense of soybean meal (5.4 TIU/mg) to create the experimental diets. Diet formulation was based on analyzed nutrient values of the soy flour and soybean meal, assuming digestibility coefficients for soy flour were equivalent to those of soybean meal. Experimental diets were fed in three phases: phase 1 from d 0 to 10, phase 2 from d 10 to 24, and phase 3 from d 24 to 42 after weaning. Feces were collected from three pigs per pen on d 10 and 42 to determine fecal DM, and d 42 fecal samples were used to determine apparent total tract digestibility (ATTD) of DM and crude protein (CP). Across all three individual phases and overall (d 0 to 42), increasing TIU decreased (linear, P < 0.001) average daily gain (ADG), average daily feed intake (ADFI), and gain:feed ratio (G:F). Fecal DM on d 10 increased (linear, P < 0.015; quadratic, P = 0.088) as TIU increased, with the majority of increase in fecal DM observed as trypsin inhibitor increased from 3.5 to 4.9 TIU/mg of complete feed. However, there were no differences in fecal DM on d 42. The ATTD of DM decreased then increased (quadratic, P = 0.003) as TIU increased with the lowest ATTD of DM observed at 4.2 TIU/mg of complete feed. The ATTD of CP decreased (linear, P < 0.001) as TIU/mg of complete feed increased. In conclusion, these data suggest that increasing dietary TIU above 1.4 TIU/mg of complete feed linearly decreased nursery pig growth performance and reduced the ATTD of DM and CP. Based on these results, each 1 TIU/mg increase in dietary TIU was associated with a 38'g/d, or a 7.4%, reduction in overall ADG. Overall ADFI decreased by approximately 40'g/d, or 5%, per 1 TIU/mg increase. Overall G:F decreased approximately 3% per 1 TIU/mg increase. Based on the amounts of SBM used in the diets for this study, and its TIU concentrations, soybean meal with greater than 5.4 TIU/mg has the potential to decrease nursery pig performance.