Potential to Minimise Variations in Grain Quality

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1		Harris Draysey Ledvinka	--	1956	2022-12-05 08:25:54	\|
2	format correct	Catherine Yang	Meta information modification	1956	2022-12-05 12:15:17	\|

This entry is adapted from the peer-reviewed paper 10.3390/agriculture12111913

Climate change has wide-reaching consequences for agriculture by altering both the yield and nutritional composition of grains. This poses a significant challenge for the poultry industry which relies on large quantities of high-quality feed grains to support meat and egg production. Elevated atmospheric carbon dioxide concentrations (eCO₂), heat and drought overall reduce grain yield and quality.

barley climate maize nutrition sorghum wheat yield

1. Crop Migration, Sowing Windows and Management Practices

Several strategies may help to manage the effects of climate change on grain yield and nutritional quality. In agricultural systems including animal feed production, climate change adaptation can involve adjusting crop management practices, plant breeding, feed processing and feed enzyme supplementation in order to produce adequate amounts of nutritionally rich animal feed in a changing climate ^[1].

Crop migration is an example of adjusting crop management practices. It involves moving crops to different geographical regions to adapt to changing climatic factors ^[1]. This can include abandoning existing growing locations, expanding into new regions and cultivating different crops that are better suited to new climatic conditions ^[2]. Crop migration helps to mitigate changing growing season temperatures and is already occurring worldwide ^[1]^[2]^[3]. This can be reinforced using supplementary irrigation which helps to counteract the effects of drought on grain yield and nutritional quality ^[2]^[4]. However, as Mariem et al. ^[5] note, neither crop migration nor irrigation may mitigate the effects of eCO₂ which influences crops regardless of latitude.

An alternative cost-effective strategy for adapting to climate change is adjusting sowing windows. This involves timing the sowing of crops so that plants flower at the optimum flowing window when environmental conditions are favourable. Recent literature has found this to be a promising method for alleviating the negative effects of climate change on grain yield and quality ^[6]^[7]^[8]^[9].

Finally, other crop management practices such as zero tillage and stubble retention may offer short-term yet cost-effective strategies for adapting to climate change impacts including drought stress. Zero tillage and stubble retention may increase soil water storage by reducing evapotranspiration and runoff, thereby reducing the impact of drought stress on crops ^[10]^[11]. However, the consensus among existing literature is that zero tillage does not function as a one-stop solution. For example, Liu ^[9] found that zero tillage reduced yield loss under climate change scenarios compared with conventional tillage; however, it could not reverse this effect unless combined with the use of adapted crop cultivars. Similarly, Phogat et al. ^[10] found that zero tillage was most effective at increasing water productivity when it was combined with the control of weeds and stubble retention, which involves the maintenance of crop residue to suppress evapotranspiration.

These strategies may offer cost-effective solutions to climate change, enabling producers to counter the effects of climate change on grain yield and quality reductions. However, as climate change continues to alter growing conditions, animal feed production may need to rely on more long-term solutions for mitigating climate change. For example, while crop migration may offer a short-term solution for adapting to changing environmental conditions, it (i) does not counter the effects of eCO₂ ^[5], (ii) may be environmentally harmful by reducing wildlife habitat area and biodiversity ^[2] and (iii) disproportionately places vulnerable populations at a higher risk of economic and social insecurity ^[1]^[3].

2. Plant Breeding

Another strategy for reducing climate impact on grain quality and yield is through breeding programs. In conventional breeding with genomic selection, a highly diverse set of agronomically adapted plant materials is assembled for phenotyping. This is supported by genomic selection where a reference population is phenotyped for the trait of interest using several DNA markers including Single Nucleotide Polymorphisms (SNPs) across the whole genome. One example is the selection of heat-tolerant wheat at the Plant Breeding Institute at the University of Sydney using a three-tiered approach ^[12]. First, multiple genotypes were evaluated in replicated field plots at different times of sowing. This was followed by the evaluation of later sown materials under high-temperature stress and selection based on estimated genomic breeding values. Materials identified as heat-tolerant in the field were subsequently evaluated in field heat chambers set at 4 °C above the ambient temperature to induce heat shock during reproductive development and grain filling to confirm heat tolerance. Finally, those lines that demonstrated heat tolerance characteristics in the field heat chambers were screened in temperature-controlled greenhouses to assess pollen viability under heat stress. Materials that survived all three stages of testing were considered highly heat-tolerant. Moreover, a common method of investigating the impact of eCO₂ on crop plants is free-air CO₂ enrichment experiments which are useful for measuring crop physiological and yield responses but less economical with limited suitable genotype options.

Controversially, there is inconsistent consumer acceptance of genetically modified food and animal feed in Australia and overseas. Emerging gene editing (GE) technologies including CRISPR-Cas9 have shown promise and despite gene-edited crops being regulated as GM crops in Europe and New Zealand, the Australian Office of the Gene Technology Regulator recently announced that gene-edited crops using SDN-1 (site-directed nuclease) techniques will not be classified as GM crops, bringing Australia in line with regulations in Japan, Brazil, Canada and USA ^[13]. This is because gene editing only cuts DNA in a specific location, and the natural DNA repair process of the cell is allowed to work; consequently, gene editing is considered similar to changes that occur in nature. It has been demonstrated that it is possible to alter nutrient composition in sorghum via GM or GE. Godwin ^[14] reported the success of developing sorghums with high protein ranging from 135 to 161 g/kg in comparison to 98 g/kg crude protein in Liberty sorghum and 126 g/kg crude protein in Cracka sorghums. Moreover, altering the expression of regulators of grain size has been demonstrated to modify grain size in transgenic sorghums ^[15].

3. Feed Processing

Climate-induced stressors increase variation in grain quality by influencing grain nutrient profile. High variability in grain quality and chemical composition will decrease the accuracy and the degree of precision in least-cost diet formulations. Certain techniques and procedures may counteract the impact of variations in grain quality on the accuracy of feed formulations. Feed processing and the use of exogenous enzymes are among the most promising and cost-effective technologies applied to improve the availability of nutrients and destroy anti-nutritive factors present in some ingredients. Feed processing includes processing single feed ingredients or complete feed prior to presentation to the animals. Feed processing may destroy or deactivate some anti-nutritive factors in feed ingredients and enhance the rate and extent of nutrient digestion and their utilisation. For example, the heat applied during oil extraction destroys trypsin inhibitors in soya beans and deactivates the enzyme myrosinase which hydrolyses glucosinolates into toxic metabolites in canola seeds. However, excessive heat processing and grinding increase the solubility of NSP, which in turn increases the viscosity of the digesta ^[16], negatively impacting animal performance. Processing temperatures above 105 °C may also promote the occurrence of Maillard reactions which denature protein structure and reduce the bioavailability of amino acids and proteins.

A combination of technologies including de-hulling, cracking and physical grinding, in conjunction with hydrothermal processing such as steam-flaking, pelleting, expansion and extrusion, is used to process different feedstuffs and manufacture mono-gastric diets. The extent of particle size modification, processing temperature, pressure and retention time during steaming and conditioning are considered the main processing parameters which determine the physiochemical properties of processed feedstuffs and diets ^[17]^[18]. These factors could directly influence the impact of processing on feedstuff anti-nutritive metabolites, availability and the digestion site of nutrients, and thus indirectly influence animal performance and feed cost. Heat treatment of grain prior to diet mixing is very rare for pig and poultry feed. Cracking the pericarp is the simplest processing technique used to expose the endosperm and enhance grain digestion by most animals. Particle size reduction via milling is the next most efficient way to increase the surface area for endogenous enzymes to digest starch and protein. However, it is worth noting that particle size should be optimised based on animal species and stage of production. Feeding coarsely ground maize and wheat has been reported to increase gizzard weight and function, decrease gastrointestinal pH in broiler chicks ^[19] and layer hens ^[20], and reduce stomach ulcerations in pigs ^[21].

During steam-pelleting, starch in the feed may be gelatinised by heat and steam during the conditioning process. Starch gelatinisation improves starch digestibility and also acts as a pellet binder to enhance pellet durability and hardness. Other processing techniques such as steam flaking, extrusion, micronisation, microwave and chemical treatments are used to change grain density, break the grain coat and endosperm, release nutrients (starch and protein bodies) and expand the surface area for enzymatic digestion. However, these techniques are not commonly applied or have very limited application to feed ingredients used in mono-gastric diets.

4. Feed Enzyme Supplementation

Grain inclusion in mono-gastric diets can account for up to 60–70% of the metabolisable energy and 30–35% of the protein requirements of animals. Therefore, variation in grain quality is expected to have a major impact on performance parameters ^[22]. Dietary feed enzymes have long been used to improve animal production output, particularly when ingredient variability is perceived to limit the predictability of performance ^[21]^[23]. The benefits of using feed enzymes in mono-gastric diets include not only enhanced growth performance and improved feed efficiency but also fewer environmental problems due to reduced output of undigested nutrients in excreta. Increased accuracy and flexibility in least-cost feed formulations and improved well-being of animals are other possible benefits of using feed enzymes. Exogenous feed enzymes have a stronger impact on poor-quality ingredients than on higher-quality ingredients ^[24]. The mode of action of exogenous enzymes is described by several possible mechanisms: the breakdown of antinutritional factors present in feed ingredients, the elimination of nutrient encapsulation effect and thus increased nutrient bioavailability, the breakdown of specific chemical bonds in raw materials not cleaved by endogenous enzymes, the release of more nutrients, and complementation of the enzymes produced by young animals ^[24]. Therefore, the principal reason to use exogenous feed enzymes is that they improve the digestibility of several nutrients, specific to the enzyme employed, and as such, can be used to counteract the negative impact of climate-induced stressors on the chemical composition of grains.

Feed enzymes are mainly dominated by carbohydrates and phytase ^[25]. The anticipated improvement in productive traits from exogenous enzyme application has been reported to be closely associated with an improvement in nutrient and energy utilisation ^[26]. Scott et al. ^[27] reported increased AME content of different wheat cultivars (10 samples) in response to dietary enzyme supplementation and pelleting in broiler chickens. This improvement was followed by reduced variations in wheat AME values. NSP-degrading enzymes are principally designed to act on NSP and spare more energy from the diet energy; however, some evidence suggests that amino acids are also spared by using exogenous carbohydrases, particularly in diets based on viscous grains such as wheat and barley ^[24]. The most common fibre-degrading enzymes used in pig and poultry diets are β-glucanase, xylanase, pectinase, hemicellulose and cellulose. Different feedstuffs have different amounts and structures of fibre; as a result, the selection of enzymes for each feed ingredient is important for improving the nutritional value of feed and possibly reducing the variations in grain quality ^[28]. A prime example of this is the use of ß-glucanase in barley-based diets and xylanase in rye- or wheat-based diets. Xylanase and β-glucanase are considered effective at decreasing intestinal viscosity, thus increasing the digestibility of nutrients including energy and amino acids ^[29]. The use of xylanase in both pig and poultry rations leads to a constant improvement in the digestibility of the undigested fraction of fibre and amino acids ^[30]. Many nutritional and environmental factors may influence the response of animals to enzyme supplementation of the diet including cereal type, breed, growing environment, cereal inclusion rate, the age of the animal, pelleting of diet, age at first exposure to the enzyme and fat type and inclusion rate.

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Subjects: Agriculture, Dairy & Animal Science

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Harris D. Ledvinka

Mehdi Toghyani

Daniel K. Y. Tan

Ali Khoddami

Ian D. Godwin

Sonia Y. Liu

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Update Date: 06 Dec 2022

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