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The effect of trypsin inhibitor unit concentrations from raw soybeans in grower pig performance and protein digestibility

Miller, K., M. Nisley, O. Mendoza, J. Spencer, H. Krishnan and N. Gabler
2024

Soybeans contain two major protease inhibitors, Kunitz trypsin and Bowman-Birk protease inhibitors, both of which are antinutritional components that can be directly linked to a reduction in amino acid bioavailability and growth performance in swine. Therefore, the objective of this study was to determine the level at which trypsin inhibitor units (TIU, expressed as TIU/mg of complete feed), coming from raw soybeans, in pig diets result in reduction in growth performance and digestibility. This study utilized 45 grower gilts (39.7 + 2.1 kg BW) that were individually penned and fed one of five dietary TIU treatments (n = 9 pigs/trt) in a complete randomized design. Diets were representative of a commercial corn-soybean meal diet and formulated to have ranging TIU/mg of complete feed of 0.89, 1.77, 3.55, 6.99, and 11.54 TIU/mg utilizing raw ground soybeans and soybean meal at incremental levels. Analyzed diets contained 0.99, 2.23, 3.07, 6.49, and 9.38 active TIU/mg. Diets were balanced to the same grams of SID Lys:ME of 2.85 and NDF concentration of 7.4% utilizing soybean oil and soybean hulls, respectively. Individual feed intake was recorded throughout, and pig BW was collected on d 0, 21, and 27 to calculate ADG, ADFI, and feed efficiency (G:F). All pigs were placed into metabolism crates on day 21 for six days to determine apparent total tract digestibility (ATTD) of nitrogen (N), N excretion and N balance. Growth performance and ATTD data were analyzed with pig as the experimental unit and diet TIU level as a fixed effect using ANOVA, linear, and quadratic contrast models. Overall, ADG decreased as diet TIU increased (1.07, 1.03, 1.02, 0.91, and 0.83 kg/d, respectively, linear P < 0.001). However, no differences in ADFI (P > 0.10) were reported and this resulted in a decrease in G:F (0.48, 0.45, 0.43, 0.41, 0.36, respectively, linear P < 0.001) as dietary TIU concentrations increased from 0.99 to 9.38 TIU/mg. Compared to 0.99 TIU/mg, pigs fed 9.38 TIU/mg had a 9.32% reduction in final BW (68.7 vs. 62.3 kg, linear P < 0.001). Apparent total tract digestibility of N decreased when pigs were fed 9.38 TIU/mg compared to 0.99 and 2.23 TIU/mg (83.26% vs. 90.29% and 89.57%, respectively, P < 0.001).

In conclusion, as total trypsin inhibitor units increase in complete feed of grower pigs, digestibility of protein, growth rates and feed efficiency are reduced in a linear manner.