The Amino Composition of Organic Soybean Meal for the Formulation of Organic Poultry Feed

Organic poultry production has increased greatly over the past several years as consumer demand has risen. Organic broiler chicken sales rose last year by 78% to $750 million, making it the largest growing market in the organic sector (United States Department of Agriculture [USDA], 2017). Proteins are a large group of compounds that are essential in animal physiology (Groff and Gropper, 2000; Razani et al., 2002). They are necessary for the growth and maintenance of animals and are provided in the ingredients in poultry feed. Proteins are digested into small peptides and amino acids. These amino acids are reused as the building blocks in the body's protein biosynthesis (Chalova et al., 2009). There are twenty amino acids that are derived from plant and animal feedstuffs (Reid et al., 2006). Some amino acids cannot be synthesized by chickens. These are called essential amino acids (EAA) and must be supplied in their diets (Reid et al., 2006). The EAA that is present in dietary protein in the least amount relative to the animal's requirement for that EAA is referred to as a limiting amino acid. Protein synthesis is hindered by the first limiting amino acid. The limiting essential amino acid limits the utilization of all the other amino acids. Methionine (MET) is predominantly the first limiting amino acid in poultry diets, which are most commonly formulated with corn and soybean meal (Chalova et al., 2016).

Plant protein sources are typically the byproduct meals of oil extraction. The amino acid profile of soybean meal complements that of cereal grains (such as corn) to help meet the amino acid requirements of the bird. Specifically, corn has lower levels of lysine and arginine relative to a bird's requirement. However, the amount that is in soybean meal, when blended together, provides an amino acid profile that better matches the needs of the bird. Often, however, the requirement for certain amino acids cannot be fully met through the combination of natural ingredients; therefore, purified crystalline amino acids can be added to meet the necessary requirement. Without a purified form of an individual amino acid, the only way to meet the requirement is to supply more protein (typically in the form of more soybean meal). This results in an oversupply of all of the other amino acids, leading to excess nitrogen for the bird to excrete, and excess nutrient levels in the litter.

The regulations and guidelines for organic poultry in the United States are provided by the USDA National Organic Program (NOP) in 7CFR§205.2. Synthetic substances that are allowed for use in organic poultry production are listed in §205.603. The organic producer faces some challenges since, currently, no synthetic amino acids are allowed in organic poultry feeds except a limited amount of synthetic DL-methionine (DLM) under §205.603(d), which permits 2 pounds DLM per ton of organic broiler and layer feeds, and 3 pounds of DLM per ton of turkey and all other organic feeds. To avoid the inclusion of synthetic methionine in animal feed, high methionine maize (high-MET) varieties that contain up to 50% higher levels of methionine were developed (Phillips et al., 2008). Jacob et al., (2008) concluded that this high-MET maize was a suitable replacement for conventional maize; however, the Methionine Task Force (2008) inferred that the lower yields and high cost of high-MET maize would deter many farmers from using it.

While it is not the main protein source in poultry feed, soybean may be used to complement the diet to ensure that adequate amounts of the essential amino acids are available to the birds (Gandhi et al., 2008).

We conducted a study to evaluate the amino acid content in organic soybean meal and compared it to the amino acid content in conventionally-grown soybean meal (Table 1). The organic soybean meal was obtained from commercial suppliers of organic feed ingredients, and the conventional soybean meal was also obtained from a commercial supplier. Not only must organic soybean meal come from organically farmed soybeans, another key difference is that organic soybean meal must have the oil extracted via a mechanical process. Conventional soybean meal will have the oil removed via a solvent extraction process. With the mechanical process, more oil remains in the by-product meal, affecting both energy content and amino acid levels. Soybean has a high protein content and highly digestible amino acids which would make soybean meal a useful supplement in monogastric diets (Meng and Slominski, 2005; Gandhi et al., 2008).

The crude protein and individual amino-acid content of organic soybean meal compares favorably with that of conventionally-grown soybean meal (Table 1). The digestibility of the essential amino acids in the organic soybean meal is high and also compares favorably with the conventional soybean meal. As in conventional poultry diets, organic poultry diets should be formulated with organically-grown soybean meal because the digestibility of the amino acids in organic soybean meal is similar or higher than in conventional soybean meal.

Table 1: Essential Amino Acid Content and Digestibility of Organic Soybean Meal and Conventional Soybean Meal 

Acknowledgement

This research was supported by funds from USDA Organic Transition Grant 2014-51106-22093.

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