Soy and soybean meal use in the feed industry; formulation and quality considerations. J. E. van Eys. G.A.N.S. Inc. Introduction. On a global scale soybeans are the primary vegetable protein source in animal feed. The use of soybean in animal feed has grown steadily, reaching 125 million metric tons in 2001 (USDA, 2002). Despite some regional and seasonal fluctuations, the increase in soy protein use in animal diets accelerated over the past 3 years averaging 5 % per year. Consequently, soybeans account for most of the increase in world production of protein meals . The increased use of vegetable protein meals in animal feeds has been especially pronounced in W. Europe where legal restrictions have virtually eliminated the use of animal proteins from feeds. Countries outside the EEC, especially in Central and East Europe, have implemented similar legislation while others are adapting feed formulations to increase the use of plant proteins. With the increased use of vegetable protein sources, the importance of protein quality and the methods used to control quality have increased proportionally. This is evident in the case of young-animal nutrition where protein quality is a major factor in early growth and performance, but it is equally important in the feeding of older animals where feed cost and feed conversion are major economic parameters. The selection of soy bean meal for specific purposes and the application of different quality criteria as selection tools have thus become increasingly important steps in diet formulation and feed production. As a matter of fact, in a recent survey of West European Feed manufacturers, quality and consistency of quality were evoked as the main reason why feed compounders selected soybean meal of a specific supplier (West, 2002). The correct and detailed description of the soybean product and the strict application of quality criteria are therefore essential pre-requisites to maximizing the efficient use of soy products under modern least cost formulation settings. Soy meal differentiation. Many different types of soy products are marketed and used in the animal feed industry. Classification of the various types of soy bean products depends largely on the specific association or organization dealing with the product. Traders and raw material suppliers will generally prefer a limited number of classifications. For the classical soybean meals typical specifications have therefore been established and these are often used as reference values in trading or classification. Table 1 gives the NOPA (National Oil Processors Association,1997) specifications for Solvent extracted soybean meal and for Dehulled soybean meal often referred to as Lo- and Hi-Pro soybean meal. These minimum quality standards allow the establishment of trading rules and adjustments for quality in case of disputes involving nutrient concentrations. They are often completed with additional quality recommendations related to color, odor, texture, contaminants, ash levels and protein quality characteristics (see below). Table 1. Specifications for Solvent extracted and Dehulled Soybean Meal (%). Min./Max. Solvent extracted SBM Dehulled Soybean meal Moisture Max. 12.0 12.0 Protein 44.0 47.5 - 49.0 Fat Min. 0.5 0.5 Crude Fiber Max. 7.0 3.3 - 3.5 Anticacking agent Max. 0.5 0.5 Specifications such as these may vary among organizations and regions and although they provide a solid basis for commercial transactions they are inadequate and of limited value when formulating diets. Formulators, seeking to maximize the value of a raw material and minimize formula cost often prefer to separate raw materials beyond trader classifications. Common criteria of segregation are origin, supplier and especially quality characteristics often combined with chemical composition. This holds true for all raw materials including soybean meal. Under these conditions, storage capacity and the number of silos or bins at the production facility become the major limiting factor. An additional, important criterion for the separation of soy meals is the use of the ingredient in specific diets. For instance, dehulled SBM will be used preferentially in poultry diets and solvent extracted SBM in swine diets. While segregation on the basis of chemical composition and quality criteria is largely internal and dictated by company-specific formulation practices, the separation according to species agrees to a large extent with the classification applied by buyers and traders. Table 2. presents a summary of the main types of soybean products used in animal feeds and the maximum level of incorporation in diets of specific livestock. Table 2. Composition of some soybean products and their use in mature animal diets1. Cooked Full- Expeller Ext. Solvent Ext. Dehulled Soy Protein Fat Soybeans SBM SBM SBM Concentrate Soy Isolates Dry matter % 90 89 90 89 93 94 Crude protein % 38 42 44 49 68 88 Ether extract % 18.0 3.5 0.5 1.0 3.3 1.5 Crude fiber % 5 7 7 3 4 2 Ash % 5 6 6 6 7 3 Poultry ME kcal/kg 3350 2420 2240 2475 2890 3295 Swine ME kcal/kg 3650 2990 3090 3380 3500 3560 Amino acids ----- ----- ----- ----- ----- ----- Methionine % 0.54 0.60 0.65 0.75 0.90 1.01 Cystine % 0.55 0.62 0.67 0.74 1.00 1.19 Lysine % 2.75 2.70 2.90 3.20 4.20 5.26 Threonine % 1.60 1.70 1.70 2.00 2.80 3.17 Tryptophan % 0.52 0.58 0.60 0.70 0.90 1.08 Maximum levels used in selected species (%)2: Ruminants 10 40 40 35 ---- ---- Swine 10 40 40 30 25 ---- Poultry 10 40 40 35 30 ---- Pet foods 2 3 3 4 6 12 1 As fed basis. 2 As % in complete concentrate feed for adult animals; (vary with performance level, protein quality and other ingredients in diets). The types of soybean products shown in the above table are in line with specifications or standards for raw materials used in the feed industry. The nutrient values are averages and are typical for soybean products. They explain to a large extent the important role that soy products play in feed formulation. Their relatively high energy and protein levels associated with the typical amino acid concentrations make all of the soy products especially suited for monogastric diets. To maximize utilization of SBMs in ruminant diets soybean meals are often treated to reduce rumen degradation. The number of commercial soybean products modified through heat or the use of specific chemical components is large. Inclusion of the different protein sources in animal diets depends much on the type of diets that needs to be formulated. In the case of full fat soya, the level of unsaturated fatty acids is a major limiting factor for inclusion. For soybean meal incorporation in diets is mainly determined by the nutrient specifications of the diet and price. Table 2. provides only general guidelines for the maximum level of incorporation commonly practiced in the feed industry. These are levels used in diets for mature animals and they may change drastically, depending mainly on 3 factors: the use of other ingredients, the performance level sought or technological treatment (processing). With more intensive treatment, flexibility of incorporation will increase and the application in more sensitive age-groups or species more feasible. The more elaborated soy products such as isolates and soy protein concentrates are used almost exclusively as high quality protein sources in diets for young animals or in aqua diets and pet foods. Cost constraints are the main reason why such products are not used in older animals. On the other hand, extrusion or similar more intensive treatment of full-fat soybeans or SBMs can be used to increase their inclusion in diets for young animal or aquatic species. Nutritional aspects. Compared to other sources of plant protein, soy products stand out by their large diversity and their advantageous levels of many critical nutrients. This is especially true where it concerns the use in concentrate feeds. At the same protein levels, fiber concentrations are generally low and metabolizable energy relatively high. However since they are pre- dominantly used as protein sources, the most important criteria is the level of digestible amino acids. The lysine concentration of all soy products is high and the concentrations of other amino acids relative to lysine are fairly constant across soy products indicating that the specific treatments to which the soybeans were subjected did not affect the amino acid profile. The special elaboration and the heat treatments needed to permit inclusion of soybean products in complex diets or in normal diets at the above indicated maximum levels in normal performance diets are related to the overall digestibility or bio-availability of nutrients. Modern diets are largely formulated on the basis of digestible amino acids. In fast growing, intensively raised animals such as hogs this is normally expressed in terms of ileal digestibility. Expression of nutrients on this basis allows formulation and production of diets more closely related to real physiological requirements. Table 3 shows the digestibility and levels of ileal digestible protein and lysine in hogs. Digestibility for other monogastric species is similar. Different protein sources are presented for comparison. Digestibility of protein and lysine agree closely and this holds true for all essential amino acids. Values are generally higher for the soybean meals especially in the case of lysine. This combined with the higher levels of protein and lysine results in significantly higher concentrations of digestible protein and lysine. Soybean meals are thus clearly a more concentrated source of digestible amino acids which is especially advantages when formulating dens, high performance diets. Although table 3 presents the data for swine, t values for other monogastric species are in closely in line. Table 3. Apparent ileal digestibility and concentrations of apparent ileal digestible Protein and Lysine for swine from selected protein ingredients(g/kg)1.