Raw soybeans contain antinutritional factors such as trypsin inhibitors (TI) and lectins.  The production of soybean meal involves a heating step, which reduces these anti-nutritional factors. However, conventional soybean meal contains compounds which can cause digestive disturbances in weanling pigs. Soybean meal is therefore limited in pig starter diets. Other protein sources, such as fish meal, casein, and soy protein isolate, are used for young pigs.

Two new soybean products were recently introduced to the U.S. feed market.  Fermented soybean meal (FSBM) and enzyme-treated soybean meal (ESBM) are believed to have a lower concentration of antinutritional factors and a higher concentration of crude protein and amino acids than conventional soybean meal.  They are also believed to be better tolerated by young pigs. However, not much is known about the digestibility of the protein in these two products.

This experiment was conducted to compare the digestibility of amino acids in weanling pigs of FSBM, ESBM, conventional de-hulled soybean meal, fish meal, casein, and soy protein isolate.

The experiment

Six diets were formulated, each of which contained one of the experimental protein ingredients as the only source of protein and amino acids.  A seventh, N-free, diet was used to determine basal endogenous amino acid losses.

Seven weanling barrows were fitted with T-cannulas in the distal ileum.  Each pig was assigned to one of seven diets – six experimental diets and the N-free diet – for each of seven weeks.  Thus, each pig was on each diet for a total of one week.

Pigs were fed their diets ad libitum.  For the first five days of each period, the pigs were allowed to adjust to their diets. On days 6 and 7, ileal digesta were collected and frozen.

Composition of ingredients, diets, and digesta were chemically analyzed to determine the concentrations of crude protein (CP) and amino acids (AA). In addition, the protein sources were analyzed to determine dry matter content, ether extract, crude fiber, calcium, and phosphorus.  Apparent (AID) and standardized (SID) ileal digestibility values were calculated for each of the protein sources.

The results

The composition of the ingredients is summarized in Table 1.  FSBM and ESBM contained a higher concentration of crude protein and all amino acids than conventional soybean meal.  Casein contained the greatest concentration of crude protein and most amino acids, with soy protein isolate also higher in CP and AA than the other soy products. Fish meal contained a higher concentration of crude protein than any of the soybean meals. It was higher in most indispensable amino acids than the soybean meals, but lower in a number of dispensable AAs than FSBM and ESBM.

Table 1. Analyzed nutrient composition of soybean meal (SBM), soy protein isolate (SPI), fermented soybean meal (FSBM), enzyme-treated soybean meal (ESBM), fish meal, and casein, as-fed basis

The SID of crude protein in casein was higher than than in conventional soybean meal, fermented soybean meal, and fish meal; it was the same as the SID of CP in enzyme-treated soybean meal and soy protein isolate. The SID of most amino acids was highest in casein and soy protein isolate. SID of most indispensable amino acids did not differ among the soybean meal products.  The SID values of crude protein and amino acids in all of the protein sources are presented in Table 2.

Table 2. Standardized ileal digestibility of CP and AA in soybean meal (SBM), soy protein isolate (SPI), fermented soybean meal (FSBM), enzyme-treated soybean meal (ESBM), fish meal, and casein by weanling pigs

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

Key points

• Conventional soybean meal contains anti-nutritional factors that are not well tolerated by weanling pigs. Because of this, weanling pigs are usually fed animal proteins such as milk protein or fish meal and the inclusion of conventional soybean meal is usually kept at a minimum.
• New soybean products have been developed that are better tolerated by young pigs and also have reduced concentrations of anti-nutritional factors: fermented soybean meal and enzyme-treated soybean meal.
• Fermented soybean meal and enzyme-treated soybean meal have comparable AA and CP digestibility to conventional soybean meal, but contain more digestible amino acids than conventional soybean meal because of their greater concentration of AAs.
• It is possible that fermented soybean meal and enzyme-treated soybean meal can replace some of or all the fish meal and milk protein in starter diets fed to pigs.

This report is based on the following peer-reviewed publication:

Cervantes-Pahm, S. K. and H. H. Stein. 2010. Ileal digestibility of amino acids in conventional, fermented, and enzyme-treated soybean meal and in soy protein isolate, fish meal, and casein fed to weanling pigs. J. Anim. Sci.  Published online prior to printing as doi:10.2527/jas.2009-2677.