By Tofuko Woyengo, Crystal Levesque and Bob Thaler, South Dakota State University Department of Animal Science; and Rob Patterson, Canadian Bio-Systems Inc., Calgary, Alberta, Canada
Because of the rising cost of conventional feedstuffs for pigs, it is critical for producers to look for alternative feedstuffs in order to reduce the cost of producing pork. In order to do that, it is essential to know the nutritional value of these alternative feedstuffs and the effects of available feed additives and feed processing technologies on nutritive values of these alternative feedstuffs in order to optimize their utilization in swine diets. Recent research at South Dakota State University has looked at the nutritional value of extruded or enzyme-supplemented cold-pressed soybean cake for pigs. In this column, nutrient content and digestibility, and net energy value of extruded or fiber-degrading enzyme-supplemented cold-pressed soybean cake were determined.
The number of farmers in Western Europe and Canada who crush soybeans via cold-pressing to obtain oil for use as biodiesel is increasing. Thus, cold-pressed soybean cake (CP-SBC) is becoming increasingly available for livestock feeding. However, the utilization of CP-SBC in formulating swine diets is limited by the presence of trypsin inhibitor (TI; a heat-sensitive protein that reduces amino acid digestion in pigs). Also, nutrients present in the CP- SBC may not be as highly available for utilization by pigs because of the presence of indigestible fiber. During the production of conventional soybean meal (SBM), soybeans are dehulled to reduce fiber content, and then the processed meal is subjected to heat treatment, which inactivates TI. However, during cold-pressing, the seeds may not be subjected to an adequate amount of heat required to inactivate TI, and CP-SBC is not dehulled. Thus, there is a need to inactivate TI and increase nutrient availability in CP-SBC in order to increase utilization of CP-SBC in formulating pig feeds.
Heat treatment of raw soybean products increases their nutritive value. Also, extrusion of heat-treated soybean products can further increase their nutritive value. Finally, supplementation of fibrous feedstuffs with fiber-degrading enzymes (carbohydrases) can improve their nutritive value. However, information is lacking on the nutritive value of CP-SBC that has been derived from heat-treated soybeans, and on the effect of extrusion or supplemental carbohydrases on the nutritive value of the same CP-SBC for pigs.
A study was conducted to determine the nutritive value of CP-SBC, and the effect of extrusion or carbohydrase supplementation on the nutritive value of the CP-SBC fed to growing pigs weighing about 80 kilograms. Nutritive value in this study included the chemical composition (i.e. crude protein, fat, fiber, TI and amino acids), net energy value and standardized ileal digestibility of amino acids for un-extruded CP-SBC without or with carbohydrase, and for extruded CP-SBC.
Eight ileal-cannulated pigs weighing about 80 kilograms were fed four diets in a replicated 4 × 4 Latin square design to give eight replicates per diet. Diets included a cornstarch-based diet with CP-SBC, extruded CP-SBC and CP-SBC plus multi-enzyme (1,200 U of xylanase, 150 U of glucanase, 500 U of cellulase, 700 U of invertase, 5,000 U of protease, and 12,000 U of amylase/kilogram of diet; Superzyme CS, 0.5 grams per kilogram); and a N-free diet. The CP-SBC was the sole source of protein in the CP-SBC-containing diets. The evaluated CP-SBC had been produced by heating the soybean seed at 105 degrees Celsius for 60 minutes followed by pressing of the heated soybean seeds at less than 42 degrees Celsius (barrel temperature).
Crude protein and amino acid concentrations of CP-SBC were lower, and fat and fiber contents greater than the values that have been reported for SBM (Table 1). Extrusion did not affect crude protein and amino acid contents and TI activity, but it did reduce the fiber content of CP-SBC. Amino acid digestibility of CP-SBC was lower, and net energy value greater than the values that have been reported for SBM (Table 2).
Extrusion of CP-SBC increased net energy value and digestibility of all amino acids measured when compared to those of SBM. Supplemental carbohydrase increased the digestibility of two indispensable amino acids (arginine and isoleucine) and three dispensable amino acids (glycine, proline and tyrosine; data not presented) for CP-SBC.
Thus, the results show that carbohydrase supplementation to CP-SBC can increase the digestibility of some amino acids, and that the extruded CP-SBC could serve as an alternative source of amino acids and energy in swine diets. However, the amounts of extruded CP-SBC included in swine diets should be based on the targeted growth performance, price of CP-SBC, cost of extrusion and the IV concentration of the diet.