Evaluating soya alternatives for practical use in diets

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Criticism of the use of Soya Bean Meal (SBM) in poultry diets remains high from retailers due to the negative public perception, sustainability implication and deforestation associations. Protein remains a key nutrient within UK poultry diets; amino acids are the essential protein building blocks for growth and support of bodily functions which are primarily sought from SBM. 

SBM is protein rich with typically 46% crude protein (CP), highly digestible amino acids and relatively low anti-nutritional factors (ANF) in comparison to other protein sources.

Poultry have a unique profile of amino acid requirements, which very closely follows the same profile as SBM when combined with single methionine. Whilst theoretically possible, there are still many hurdles that need to be overcome regarding alternative protein sources and important factors that need to be considered when selecting these raw materials. In reducing the reliance on SBM, raw material selection should be done with careful consideration of some of these factors prior to implementation.

Nutrient bioavailability

An important aspect of formulating poultry diets is maximising nutrient bioavailability and precisely formulating to the birds’ requirements which vary depending on life stage. Formulating to digestible amino acid levels is key in maintaining the precise amino acid balance and not delivering excess crude protein. Excess crude protein can lead to higher nitrogen excretion and cause gut health challenges. This undigested protein can cause proliferation of harmful bacteria in the gut, which can challenge bird health and performance.

Once the amino acid profile is understood, the use of alternative protein sources can be balanced by single amino acids. Out of the 20 L-amino acids that can be synthesised from protein, poultry are unable to synthesis 9. These are called essential amino acids. Not all these essential amino acids are commercially available in the single form and the required balance will need to come from the raw materials in the diet.

Commercial availability of alternative protein sources

Once an ingredient has been evaluated to be beneficial and meet the nutritional specifications to fit into a diet, other factors need to be considered; commercial availability, processing requirements and the cost of production. Commercial availability of alternative protein sources have difficulty competing with soya, given the good supply and processing facilities of soya into the UK. Without further processing, the presence of ANF’s in many commodities will limit the inclusion in diets. For instance, the ANF’s present in soya are reduced via heat treatment during the oil extraction process. Hence, it is not only crop availability but also infrastructure requirement to enable access to sufficient tonnage in the market.

In addition to processing, additives such as enzymes can also be used to minimise ANF’s impact and further utilise nutritional value. Typically, in soya free diets we rely on multiple protein sources, which can all have different associated ANF’s. The combination of ANF’s and their impact when formulating soya free diets needs to be further understood to optimise performance.

In the last couple of years, we as nutritionists have had a growing number of requests to evaluate and implement rations with low global warming potential, whilst maintaining bird performance. This can be done through reducing soya and diets can be compared using GFLI lifecycle assessment (LCA) figures. The GFLI database is a global reference database that uses and differentiates the LCA results for macro feed ingredients. Factors such as geographic location, processing and transport are used in the calculation process. 

Comparing diets of comparable nutritional value, reducing soya can reduce C02e (kg/ton) when land use change (LUC) is included,, however when excluding LUC this is not necessarily the case. Undoubtedly, the correct selection of raw materials and careful balance of protein supply can lead to a reduction in feed carbon footprint.

The below table highlights alternative protein potentials and benefits and limitations of their selection within poultry diets.

Table of Raw Material Benefits and Limitationsalternative protein potentials and benefits and limitations of their selection within poultry dietsWith good nutritional understanding and availability of alternative raw materials it is possible to reduce soya in poultry diets. However, it should be done slowly and in managed stages. This gives both the bird and the business a chance to adapt to the changes. Adaption to reducing soya and no soya will, at present, come at a cost.