Two 28-d experiments were conducted to evaluate the effects of extrusion of ground yellow corn, solvent-extracted soybean meal (SBM), and cracked whole soybeans (CWS) individually or as corn-soybean product blends on growth performance of weanling pigs. In the first experiment, ground corn, SBM, and the corn-SBM blend were extruded at 137.5°C, 131.5°C, and 135.0°C, respectively, in a twin-screw extruder. Transit time was 60 seconds with water injected at 125 g/min during extrusion. The five treatments were the corn-SBM control diet and the diets with extruded (EX) corn + SBM, EX-SBM + corn, EX-corn + EX-SBM, and the EX-blend of corn-SBM. Ninety crossbred pigs with an initial average weight of 5.98 kg were allotted to nine treatment replications.
In the second experiment, ground corn was preconditioned with water (10.0% of corn weight), and SBM was preconditioned with water and soybean oil (each at 20.0% of SBM weight) before extrusion. Raw CWS were not preconditioned. The corn, SBM, CWS, corn-SBM blend, and corn-CWS blend were extruded at 113.0°C, 132.0°C, 132.0°C, 88.0°C, and 102°C, respectively, with a single-screw extruder. Transit time was 30 seconds. The eight isocaloric treatments were the corn-SBM control diet and the diets with EX-corn + SBM, EX-SBM + corn, EX-corn + EX-SBM, the EX-blend of corn-SBM, EX-CWS + corn, EX-CWS + EX-corn, and the EX-blend of corn-CWS. A total of 296 crossbred pigs with an initial average weight of 6.6 kg were allotted to 10 treatment replications.
Results for both experiments indicate that single- or twin-screw extrusion of ground corn or SBM as individual ingredients or as corn-SBM blends in diets for weanling pigs did not improve 28-d growth performance. However in the second experiment, weanling pigs fed the diets with EX-CWS + corn and EX-CWS + EX-corn had greater (P ‹ 0.01) average daily gains and feed efficiencies, respectively, compared to the pigs fed the corn-SBM control diet. The extrusion temperature of 102°C for the corn-CWS blend did not inactivate adequate protease inhibitors in CWS, and pigs fed that diet had poor growth performance. In conclusion, single-screw extrusion of CWS (132°C for 30 s) in diets for weanling pigs improved growth performance compared with pigs fed the corn-SBM control diet. However, twin- or single-screw extrusion of ground yellow corn or solvent-extracted SBM as individual ingredients or as corn-SBM blends in diets for weanling pigs did not improve growth performance compared with pigs fed the corn-SBM control diets.