By Diego A. Rodriguez, Su A Lee and Hans H. Stein, University of Illinois
Most soybeans are crushed using the solvent extraction procedure, which results in production of soybean meal with a very low concentration of residual oil. However, soybean oil may also be removed from soybeans using the extrusion-expeller method, which results in production of soybean oil and soybean expellers.
A patented high-shear dry extrusion process that uses a continuous pressing of oil may be used in the production of soybean expellers, which typically contain 5 to 8% oil. The greater concentration of oil in soybean expellers compared with SBM may result in increased digestibility of amino acids and energy, but this hypothesis has not been experimentally verified.
Two experiments were conducted to test the hypothesis that digestibility of amino acids, total dietary fiber, and gross energy and concentrations of digestible energy (DE), metabolizable energy (ME) and net energy (NE) are greater in soybean expellers compared with SBM.
Amino Acid Digestibility Trial
Two diets were formulated to contain either high-shear dry extrusion soybean expellers (ExPress®, Insta-Pro International) or soybean meal as the only source of amino acids. Diets were fed to ileal-cannulated pigs and ileal digesta samples were collected to calculate the standardized ileal digestibility (SID) of amino acids in each diet.
Results demonstrated that concentrations of crude protein and amino acids were less in soybean expellers than in soybean meal (Table 1), which is due to the greater concentration of oil in soybean expellers. However, the SID of most amino acids was greater (P
Graphs provided by Hans Stein.
Fiber Digestibility and Energy Metabolism Trial
In the second trial, a corn-based basal diet and two diets containing corn and soybean expellers or corn and soybean meal were formulated. Fecal and urine samples were collected from pigs placed in metabolism crates to calculate the apparent total tract digestibility (ATTD) of energy and total dietary fiber and concentrations of DE and ME. Concentrations of NE in diets were also determined using a published equation.
Results indicated that ATTD of gross energy and total dietary fiber was not different between soybean expellers and soybean meal (Table 2). Concentrations of DE, ME and NE in soybean expellers were greater than in SBM, which is likely a result of the greater fat concentration in soybean expellers.
What Did the Results Show?
Soybean expellers contain less crude protein and amino acids, but more fat, than soybean meal. Values for the SID of crude protein and amino acids in soybean expellers were greater than in soybean meal and greater concentrations of DE, ME and NE were observed in soybean expellers than in soybean meal. These results indicate that inclusion of soybean expellers in diets for pigs will increase ME and NE and SID of amino acids in the diet.
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