Alternative Feed Ingredients for Poultry Diets: Challenges and Prospects

A number of factors including the global population growth, shift towards high protein diets, finite land availability for crop production, climate uncertainties, increase in fossil fuel prices and diversion of feed ingredients, especially of cereals, to biofuel manufacture presents challenges to the global feed supply. This is a major threat for sustainable poultry production, in both the developing nations, as they move towards animal protein food regimen due to rising incomes, and developed countries that rely heavily upon a limited number of soybean meal producing nations (USA, Argentina and Brazil) (Fitches et al., 2017). According to forecasts, the demand for poultry feed will increase at a compound annual growth rate of 7.1% from 2018 to 2027, with the sale volume expected to grow beyond 890 million metric tonnes by 2027. Therefore, it is clear that the future requirements for traditional feed ingredients (maize and soybean meal) cannot be met, even according to optimistic forecasts. As a result, sourcing of quality and sustainable feed ingredients at acceptable prices has become the major challenge for the industry. The most obvious strategy is to search for potential alternative raw materials. Each region has its own range of alternative (or unconventional) ingredients and their feeding value has been researched locally. The commercial use of these ingredients, however, has been limited due to constraints imposed by several nutritional, technical and socio-economic aspects. The intention of this paper is not to review the available literature on individual ingredients that could be potentially used, but rather to provide a critical overview of limiting factors and strategies to maximise their use in poultry diets. The focus will be particularly on four main aspects: (i) definition of the term ‘alternative’ feed ingredients; (ii) limitations to use of these raw materials in poultry nutrition; (iii) strategies to overcome the nutritional challenges posed by alternative ingredients, and (iv) future prospects.

Besides the ever-increasing demand for quality conventional ingredients, scarcity in supply of these ingredients, market volatility and rising prices (sometimes unprecedented) have always encouraged poultry nutritionists to explore the usefulness of locally available ingredients, so called “alternative feed ingredients”. An alternative, also known as “non-traditional”, raw material is normally referred to as a feed ingredient that is available locally, but not regularly included in commercial poultry diets, and its nutritional value and optimum inclusion level are not well defined (Dale, 2008). However, it must be noted that the term ‘alternative’ is a relative expression, depending on the geographical region and the time period, and it is therefore difficult to draw a clear distinction between traditional and non-traditional feed ingredients. Feed ingredients that may be classified as non-traditional in one region, may actually be traditional and widely used in others. For instance, in the United States, Brazil and China (the top three global producers of chicken meat) and many Asian countries where maize is the cereal of choice (traditionally and economically), other cereals such as wheat, barley or sorghum are considered as viable alternative ingredients. Conversely, wheat remains the most commonly used grain in European Union, Canada, Australia and New Zealand with other cereals as potential alternatives during the times of scarcity or rising wheat price. Another example is palm kernel meal (PKM), which is a non-traditional feedstuff in Western Africa, but an increasingly normal feedstuff for poultry in Southeast Asia, especially in pullet and layer diets. Some ingredients may have started as non-traditional but are now being used increasingly in commercial poultry diets. Therefore, a broad definition of an alternative ingredient should also take into account the time period and region. Alternative ingredients, depending on whether or not they are previously known to the industry, can be classified to non-traditional or novel ingredients. Non-traditional ingredients constitute those that have been used only locally and their potential as a global feed ingredient has not been evaluated and acknowledged. A novel feed ingredient, however, can be defined as an ingredient previously unknown to the feed industry that has never been used on a commercial scale.

It is widely recognised that existing potential feed resources worldwide, particularly in developing countries, have been largely overlooked in many circumstances, and either unutilised and wasted or used inefficiently. Most of these alternative ingredients have obvious potential, but their use has been negligible owing to constraints imposed by nutritional, technical and socio-economic factors (Ravindran and Blair, 1991):

1- Nutritional aspects: variability in nutrient composition and quality; limited information on digestible amino acid (AA) and metabolisable energy content; presence of anti-nutritional and/or toxic factors; high fibre content; low level of energy and poor protein quality; need for nutrient supplementation (added cost); poor palatability.

2- Technical aspects: seasonal and unreliable supply; physical characteristics (bulkiness, powdery texture, dustiness); logistic issues (collection, storage and delivery), requirements for further and relatively expensive processing (de-hulling, drying, physical and thermal processing); limited research and development facilities for determining nutrient availability and optimum inclusion levels in poultry diets.

3- Socio-economic aspects: competition for human consumption; lack of desire from farmers to plant these crops due to low prices relative to other arable crops; high cost per unit of energy or limiting AA relative to conventional sources.

Three major criteria determining the regular use of an alternative ingredient in commercial diets are: i) it must be available in economic quantities, even if its availability is seasonal, ii) the price must be competitive against conventional ingredients, and iii) its nutritive value, variation and digestibility must be understood.

Before the application of alternative ingredients can be considered in the commercial poultry production, most, if not all, of their limitations must be resolved. Several possibilities are available for improving the feeding value and increasing the inclusion levels of alternative feedstuffs: a) feed evaluation, with focus on energy and digestible AA, b) formulation of diets based on digestible AA, rather than total AA, c) use of synthetic AA to balance their specifications, d) supplementation with commercial exogenous enzymes to improve nutrient and energy utilisation, and e) application of feed processing techniques.

Difficulty in assessing the nutritive value of an ingredient, due to the lack or scarcity of appropriate research or analytical facilities, is a major factor discouraging poultry feed manufacturers from considering the use of alternative ingredients. There has been keen interest in evaluating alternative feed resources over the years, especially from developing countries. However, given that only limited published data are available on digestible AA and apparent metabolisable energy (AME) of alternative feed ingredients, routine feed evaluation and continuous update of matrix values are crucial for the efficient use of these ingredients. One of the major challenges for proper feed evaluation is the lack of a standard procedure to be used in the in vivo assays. An example could be the use of different methods for measurement of AA digestibility of the feed ingredients for poultry. The digestibility of AA in feed ingredients can be measured using three different methods, namely direct, difference and regression methods (Lemme et al., 2004). The direct method, due to the simplicity of the assay and calculations, is the most commonly used assay (Ravindran and Bryden, 1999). Our recent study with PKM as an unconventional ingredient (Abdollahi et al., 2015), showed that AA digestibilities determined using the direct method were substantially lower than the corresponding coefficients determined by the difference method. This finding suggests that values determined by the direct method might underestimate the AA digestibility of low protein materials that includes the majority of alternative ingredients.

The use of an appropriate energy system is another critical issue because of the importance of energy to diet cost and bird performance. In a recent review of the procedures used for estimation of the energy content of ingredients for poultry, Mateos et al. (2018) reported extreme variation among published data on the nitrogen-corrected AME (AMEn) content of the feed ingredients. Interestingly, the reported differences in AMEn (MJ/kg) are greater for unconventional ingredients such as sorghum (1.42), barley (1.97), full fat soybean (2.13), rapeseed meal (2.64), sunflower meal (2.85), maize DDGS (3.18) and broken (polished) rice (3.56) than for the conventional raw materials like maize and wheat (1.05) and soybean meal (1.63). Therefore, although there is a wealth of data on nutritive value of ingredients for poultry, these values vary widely for most of the ingredients, in particular the alternative ingredients. The discrepancies among the available data might be due to various reasons but the reported variability justifies the urgent need for consensus on the methodology for energy evaluation, especially of non-traditional raw materials (Mateos et al., 2018). Another major constraint in the endeavour to better define nutrient quality is the lack of rapid tests to determine digestible AA content or AMEn.

When fibrous and poorly digested ingredients are considered for use, feed formulation on the basis of metabolisable energy and digestible AA is a prerequisite. Digestibility of AA is not the same in all ingredients; they are well digested in some ingredients while the digestibility is lower in others. The use of digestible AA is particularly relevant to situations where diet formulations consist of a range of alternative ingredients that are poorly digestible. A good example in this regard is the use of PKM in broiler diets. In a recent study (Abdollahi et al., 2015), we evaluated the AME and digestible AA content of a PKM sample using broiler studies. Poor digestibility of protein and AA in the PKM confirmed that formulating PKMcontaining diets based on crude protein or total AA content will fail to meet the birds’ requirement for a balanced diet and impair the growth performance of broilers. In a follow-up study (Abdollahi et al., 2016), where AME and digestible AA contents of PKM were used to formulate the broiler diets, it was shown that PKM can be included in broiler diets up to 16% with no deleterious effects on growth performance. Using digestible AA contents of alternative raw materials when formulating broiler diets holds promise to increase the range and inclusion levels of these feedstuffs in practical diets, despite the fact that they may contain less than optimal AA profiles and are poorly digested.

The differences in AA digestibility of ingredients can be effectively harnessed to improve the precision of feed formulations and meet the AA requirements. Nutritionists can achieve this effectively nowadays because of the availability and use of feed grade essential AA in synthetic forms. In order to improve the feed efficiency, reduce the nitrogen and ammonia emissions and ensure sustainable poultry production, there has been a huge interest to use reduced protein diets supplemented with synthetic AA. Despite these possibilities, there is no doubt that there would be a limit on how low we can go with dietary protein levels in poultry diets, and the further use of synthetic AA beyond this threshold might not be feasible once the minimum threshold is reached. However, the use of alternative raw materials, due to their high variability and most probably less balanced AA composition and poor digestibility compared to conventional feed ingredients, would motivate the continuous development and use of synthetic AA. When alternative ingredients are included special attention must be given to threonine supplementation. Most alternative ingredients, owing to the presence of high fibre and anti-nutrients and their effect on mucin secretion, will increase endogenous protein losses in the gut. Mucin is rich in threonine and the resultant effect will be increased threonine requirement.

Commercial application of biotechnology and acceptance of feed additives in poultry nutrition during the last two decades has offered vast opportunities to enhance nutrient utilisation, feed efficiency and productivity. Perhaps the most important additive to enter the poultry feed market is exogenous feed enzymes. The availability of glycanases (xylanases and glucanases) in the 1990’s has effectively overcome the anti-nutritive effects of non-starch polysaccharides (NSP) and enabled the increased use of viscous grains such as wheat and barley in poultry diets. In relation to alternative ingredients, feed enzymes can (i) enable the use of certain ingredients (which otherwise may not be possible), (ii) remove nutritional constraints and enable higher inclusion levels, (iii) increase the range of ingredients used in feed formulations, and (iv) reduce variability in the nutritive value between batches. Enzyme addition, in particular, uplifts the value of poor quality samples and reduces the variation among the samples of a given ingredient.

Enzyme technology will undoubtedly continue to offer new opportunities for the application of alternative and novel feed ingredients in poultry diets. However, a prudent enzyme selection and development strategy will be needed to ensure optimal enzyme match with its intended substrate. The unique feature of enzymes is that they act only on a specific site on a specific substrate. In terms of alternate ingredients, the implication is that the exact nature of the substrate must be known. However, despite advances in analytical techniques, the chemistry and structure of most target substrates (especially in alternative ingredients) are still poorly defined, which remains a constraint to finding suitable enzymes.

Feed and ingredient processing, including extrusion and pelleting, can facilitate the use and higher inclusion of alternative raw materials in poultry diets, mostly through inactivation of anti-nutritional factors, break-down of cell wall matrix as a result of the physical stress, especially in fibrous materials, and provision of greater accessibility of encapsulated cellular contents to digestive enzymes. The latter effect was clearly shown by Saunders et al. (1969) in steam-pelleted wheat bran. Microscopic examination of chicken excreta showed that the proportion of empty aleurone cells (utilised contents) was greater and the level of unutilised (residual) protein by birds decreased in the pellet diet than the mash diet.

Extrusion cooking, a high-temperature/short-time thermal treatment, although it has not been used commonly in commercial poultry feed production due to its high capital investment costs, may be a useful processing technique for some non-conventional feed ingredients. Extrusion of improved faba bean cultivars, even though they contain low tannin contents, has been shown to enhance their nutritional value in broilers through reducing the phytate phosphorus (PP), trypsin inhibitor activity (TIA) and resistant starch (RS) contents (Hejdysz et al., 2016). These researchers reported that extrusion of 5 different faba beans decreased the concentration of RS by 94% (10 vs. 182 g/kg), TIA by 50% (0.3 vs. 0.6 g/kg) and PP by 51% (1.9 vs. 3.9 g/kg) compared to raw faba beans. Extruded faba beans were also characterised by higher starch digestibility (0.970 vs. 0.773), fat retention (0.989 vs. 0.872) and AMEn (14.95 vs. 10.79 MJ/kg).

The fundamental objective of pelleting at the time of introduction to the feed industry in the mid-1920′s was to convert fibrous, bulky and less palatable blends of feed ingredients into compact pellets that facilitate easy prehension (Coffey et al., 2016). One of the most momentous changes in broiler diets since the introduction of pelleting has been the shift from fibrous, textured and poorly digestible ingredients, to low fibre, texture-less and nutrient-enriched diets. This transition not only hinders the development, functionality and health of the gastrointestinal tract, but also constrains some of the advantages of pelleting. Our recent studies with maize- (Abdollahi et al., 2018) and wheat-based (unpublished data) diets, have clearly shown that the pellet-associated benefits were more pronounced in low nutrient density diets containing alternative ingredients such as wheat bran, PKM and canola meal, than high density diets based on conventional ingredients. Pelleting can attenuate the negative effects of feeding bulky, fibrous and less nutrient dense diets on broiler growth performance and facilitate higher incorporation of less desirable alternative ingredients into practical broiler diets. However, this potential of the pelleting process is not being efficiently harnessed due to the global shift towards high density diets that demands the use of conventional feed ingredients.

Local market conditions and production objectives are major drivers for the application and setting the inclusion levels of alternative ingredients in poultry diets. In countries such as Australia and New Zealand where the poultry production aims towards maximising the biological performance rather than economic performance, the use of alternative raw materials, unless there is scarcity in the supply of conventional feed ingredients, might not be so attractive. However, in some parts of the world where the industry follows a business model of economic-oriented goals rather than maximum biological productivity, alternative ingredients can make a useful contribution to poultry diets and be included even beyond maximum inclusion limits. Whilst the immediate prospects for the use of alternative ingredients will be in semicommercial poultry units that employ some degree of on-farm feed mixing, the greatest potential for using these ingredients is in the feeding of layers, irrespective of the production system. Owing to physiological differences, pullets and laying hens are more tolerant to high fibre, poor-quality ingredients and nutritional challenges than fast-growing modern broilers. Rice bran is a good example of this tolerance that can be used at maximum levels of only 10 percent in broiler diets, but may be safely incorporated into pullet and layer diets at levels of up to 30 percent.

There is a potential for fibrous alternative sources to improve the upper gut development and functionality in modern broilers. Enhancing the feed structure through the inclusion of ingredients with insoluble fibre sources holds a promise to mitigate the concerns around the sub-optimal functionality of the upper part of the digestive tract and gut health that has been an issue with feeding highly processed diets and exacerbated in light of antibiotic free poultry production. Layers not only are able to better utilise high fibre ingredients, but a recent study (Abdollahi et al., 2017) also showed that the function of the digestive tract in layers is even more sensitive to feed structure than for broilers and pullets, emphasising the importance and need for high fibre raw materials to be included in layer feeds.

The ban on the use of non-organic feed ingredients in organic poultry production has made this production system an appropriate sector for the use of alternative ingredients. Free range production systems, developed to meet the consumer demand for natural feeding and better bird welfare, may also serve as a sector for the application of alternative raw materials. Slow growing broiler strains, although not the best choice for sustainable agriculture, are becoming increasingly popular especially in Europe and can be a potential market for the utilisation of alternative ingredients.

With the exception of soybean meal which remains the sovereign protein source in poultry diets globally, other ingredients, including maize and wheat, might be considered as alternative ingredients depending on the geographical location. Although there is an extensive list of raw materials of plant or animal origin that can be used in poultry feeds in different regions, only some of these potential ingredients are highlighted in Table 1. This list is by no means an exhaustive one, but mentions some of the overlooked or undervalued ingredients that have promise for use in poultry diets on a more regular basis.

Demand for poultry products will continue to escalate over the coming decades. This high demand, along with the fact that chicken is the most sustainable farm animal species, will create an opportunistic scenario for the poultry industry. However, the ever-growing poultry industry should address, among others, the challenge of supplying adequate and sustainable feed resources. The poultry industry should not wait for a crisis, but be prepared, as global feed resources are limited, to meet the quest for sustainable production.