Study: Digestible energy in processed soybean products

Soybean meal is the most common source of protein in swine diets in the United States. However, conventional soybean meal contains antinutritional factors such as antigenic proteins, oligosaccharides, lectins, and trypsin inhibitors that limit its use in diets fed to weanling pigs. Methods of processing soybean meal to remove antinutritional factors have been developed. These include enzyme treatment, fermentation, and the removal of soluble carbohydrates.

Like soybean meal, rapeseed products are usually not fed to weanling pigs due to the presence of glucosinolates and relatively high concentrations of fibre in these products. Previous research has shown that fermentation of soybean meal can reduce antinutritional factors and fiber concentrations. An experiment was conducted to determine the apparent total tract digestibility (ATTD) of energy and concentrations of digestible (DE) and metabolisable (ME) energy in four sources of processed soybean products, conventional soybean meal, conventional 00-rapeseed expellers, and in a fermented mixture of co-products including 00-rapeseed expellers, wheat bran, potato peel, and soy molasses.

Experimental ingredients and diets

A total of 64 barrows with an average initial body weight of 19.81 kg were fed one of eight diets. The four processed soybean products were two sources of enzyme-treated soybean meal (ESBM-1 and ESBM-2), extruded soybean meal (SBM-EX), and soy protein concentrate (SPC). Another diet contained conventional soybean meal (SBM-CV). Two rapeseed products were also tested: conventional 00-rapeseed expellers (RSE), and a fermented co-product mixture (FCM) containing 00-rapeseed meal, wheat, soy molasses, and potato peel. One diet was a corn-based basal diet. Seven diets each contained corn and one of the seven test ingredients as the sole sources of energy. The test ingredients were included at levels that were expected to result in isonitrogenous diets.

Results

The ATTD of gross energy was greatest (P < 0.05) in conventional soybean meal (Table 1). ATTD values for gross energy did not differ among ESBM-1, ESBM-2, SBM-EX, and SPC. The ATTD of GE was least (P < 0.05) in RSE and FCM, which did not differ from each other.

On an as fed basis, ESBM-1, SBM-EX, and SPC contained the greatest (P < 0.05) concentrations of both DE and ME. DE and ME concentrations did not differ among ESBM-2 and SBM-CV. RSE had less (P < 0.05)  DE than ESBM-2 and SBM-CV, and FCM had the least (P < 0.05)  DE. ME values of RSE and FCM did not differ, and were less (P < 0.05) than in all of the soy products.

On a dry matter basis, DE and ME concentrations were greatest (P < 0.05) in ESBM-1, SBM-EX, SPC, and SBM-CV. ESBM-2 contained less (P < 0.05)  DE than all other soy products except SBM-CV, and less (P < 0.05)  ME than all other soy products. RSE and FCM contained the least (P < 0.05) DE and ME. Table 1. Concentrations of digestible and metabolizable energy and apparent total tract digestibility of gross energy in enzyme-treated soybean meal, extruded soybean meal, soy protein concentrate, conventional soybean meal, conventional 00-rapeseed expellers, and a fermented co-product mixture containing fermented 00-rapeseed expellers, wheat, soy molasses, and potato peel

a-d Means within a row lacking a common superscript letter differ (P < 0.05).

Key points

• ESBM-1 and extruded soybean meal had greater concentrations of digestible and metabolisable energy than conventional soybean meal.
• The digestibility of energy and the concentrations of digestible and metabolisable energy were less in rapeseed products than in soy products.
• The reduced energy digestibility in rapeseed products is due to their higher fibre content relative to soy products.

This report is based on unpublished data by Diego Navarro, Yanhong Liu, Thomas Bruun, and H. H. Stein.
University of Illinois at Urbana-Champaign