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Nutrient digestibility of soybean products in grower-finisher pigs

Yáñez, J., T. Woyengo, R. Jha, T. Van Kempen and R. Zijlstra

Solvent extraction of soybean creates soybean meal (SBM), but an array of other soybean products can be created using further processing of SBM or soybean. For accurate inclusion of these products in pig feed, characterization of digestible AA profile and energy value is required. Soybean products from processes such as extrusion (EX) of soybean and thermo-mechanical (TM) treatment, bioconversion using fermentation or enzymes (BC), and ethanol-water extraction (EW) of soybean meal were collected together with SBM. These 9 soybean products were tested in cornstarch-based diets together with an N-free diet for a total of 10 diets. Ten ileal-cannulated barrows (30.4 ± 0.7 kg initial BW) were fed 10 diets at 2.8 times maintenance DE for six 9-d periods with a 6 (periods) × 10 (pigs) Youden square. The control SBM contained 47.0% CP, 1.4% ether extract, and ADF 6.0%. The 9 soybean products contained 35.6% to 66.4% CP, 0.9% to 21.6% ether extract, and 4.4% to 8.0% ADF. The EW soybean products were high in CP (>61%), whereas the 2 EX soybean products were low in CP (<36%) but high in ether extract (≥19%). Chemically available Lys ranged from 92.6% to 100% of total Lys, indicating that minor Lys damage occurred during processing. The apparent total tract digestibility (ATTD) of energy was lower (P < 0.05) for soybean products with greater ether extract and ADF content than SBM, and varied among soybean products. The standardized ileal digestibility (SID) did not differ (P > 0.05) among soybean products for most AA, except for lower SID of Arg, Ile, Leu, Lys, Phe, and Tyr (P < 0.05) for EX2 and BC1 than other soybean products. The DE and predicted NE value did not differ (P > 0.05) among soybean products. The greater SID AA content (P < 0.05) in EW, BC, and TM1 soybean products than SBM was mainly a result of greater total AA content due to removal of other macronutrients.

In conclusion, extrusion of soybean creates soybean products with a greater energy value but lower ATTD of energy and lower SID AA content than SBM. Further processing of SBM creates soybean products with greater CP and SID AA content but similar SID of AA than SBM. Thus, new technologies to process SBM or soybean create high-value ingredients to be included in pig diets, especially for young pigs with high nutritional requirements.