DDGS: Alternative grain resource in poultry feed industries
Dr. Amit Ranjan, PhD (Animal Nutrition), Patna, Bihar
E-mail: narsidhant@gmail.com; Mobile: +91-9939337208
Introduction:
Distiller’s dried grain with solubles (DDGS) is a most common valuable co-product of ethanol (green source of energy; Canadian Renewable Fuels Association, 2011) and beverage industry. DDGS have been widely used as highly nutritious and economical feed resources (Noll, 2008). The demand of soybean, maize and other grains in the global market is ever increasing, causing a sharp increase in price, making the situation of the feed industries even worse. Thus DDGS has the ample opportunity to be utilized as an alternative grain resource in feed industries (Shurson, 2003). On the other hand, the production of ethanol increased rapidly in recent years and continuous expansion is expected in the coming future (Licht, F.O., 2010) because of energy crisis being a worldwide concern, especially with the increasing prevalence of vehicles which consume a large amount of gasoline and diesel produced from fossil fuels. Now a day, ethanol is being advocated as a substitute for fossil fuels to alleviate the stressful social and environmental pressure (Natural Resources Canada, 2011).
Distillers Dried Grains with Solubles was “the product after the removal of ethyl alcohol by distillation from the yeast fermentation of a grain or grain mixture by condensing and drying at least three-quarters of the solids of the resultant whole stillage by methods employed in the grain distilling industry” (NRC, 1984).
As the production of ethanol increased rapidly, increased quantities of DDGS are available to poultry feed industry, and this has rekindled the interest of increasing DDGS incorporation in animal diets. DDGS has been recognized as a valuable source of energy, protein, water-soluble vitamins and minerals for poultry (Wang et al., 2007a) as well as a good source of xanthophylls (Runnels, 1957), linoleic acid (Scott, 1965) and other nutrients of importance to human health, such as lutein and choline. The differences in DDGS diets may result in nutritional differences in egg yolk, such as fat content, fatty acid composition, cholesterol, choline and lutein content. Eggs are very important human food, and their compositions are of great influence for our nutrients intake. The higher inclusion rates of DDGS for laying hens may change the nutritional value of eggs that may have positive effect on human health. Several studies have indicated that brewery waste included in diets improved the growth rate and feed conversion, and also increased fertility and hatchability in poultry (Kienholz et al., 1967).
Bioethanol and DDGS processing technique
The principle of bioethanol processing is to convert feedstuffs to ethanol via a series of procedures including fermentation, distillation and drying (Nichols and Bothast, 2008). The conversion from substrate (corn, wheat, barley, rice and triticale) to ethanol is similar for all starch-based feedstuffs. Starch is first converted to glucose with the intervention of enzymes. Glucose is fermented into ethanol by yeast (Nichols and Bothast, 2008). Two different methods i.e. dry milling and wet milling are generally used to convert feedstuffs to ethanol (Nichols and Bothast, 2008). The dry grinding process grinds the whole kernel of grain for ethanol fermentation in order to get a high ethanol yield (Rausch and Belyea, 2006). The co-products of a dry grinding ethanol plant are carbon dioxide and distillers grains. The dry milling process is dominant over wet milling.
Figure 1 illustrates the technique of the production of ethanol and DDGS.
1. Wet milling
Wet milling starts with softening kernels by soaking or “steeping” the kernels in water and dilute sulfurous acid for 24 to 48 hours at 55°C and is followed by degermination (removal of germ) and processing to recover the oil. After the germ has been removed, the remaining corn kernel is screened to remove the bran, which is combined with other co-product streams to produce corn gluten feed. The starch slurry is allowed to pass through centrifugal separators, which causes lighter gluten protein to float to the top. This material is then dried and used as corn gluten meal (Davis, 2001). Wet milling can utilize both corn and wheat for ethanol production, although there are differences in the way protein and starch is separated. After the protein-starch separation, the processes converting starch to ethanol are the same for corn and wheat wet milling techniques (Graybosch et al., 2009).
2. Dry milling
(i) Grinding and mixing
The first step in the dry milling process is the grinding of feedstuffs either by a hammer mill or a roller mill to crush grain kernels in order to create smaller particles (Rausch and Belyea, 2006) because particle size of the grain can affect ethanol yield (Kelsall and Lyons, 1999) therefore, use finely ground corn to maximize ethanol yield. The grinding step allows the starch granules to react with enzymes (Nichols and Bothast, 2008). The ground particles will be blended with water forming slurry which will be “cooked” to kill unwanted lactic acid producing bacteria (Davis, 2001). The starch in the slurry will be degraded with the involvement of amylase (Rausch and Belyea, 2006).
(ii) Degradation of starch to fermentable sugars
The conversion from starch to ethanol is similar for all grains. Starch consists of two major components namely amylose and amylopectin. In amylose, which is a linear polymer, glucose units are connected by α 1-4 linkages while in amylopectin, which is a larger branched polymer, glucose units are linked by both α 1-4 and α 1-6 linkages (Drapcho et al., 2008). The ratio of amylose to amylopectin in normal starch is 1:3 except for waxy grain varieties where the starch contains about 98% amylopectin (Drapcho et al., 2008). Prior to fermentation by yeast (i.e. Saccharomyces cerevisiae), starch has to be degraded to simple six-carbon sugars via the saccharification process with the participation of heat and enzymes (Power, 2003). Initially, the pH of the slurry should be adjusted to pH 6.0 followed by the addition of the thermostable α-amylase enzyme. Swelling and gelatinization lasts about 30-45 min while the slurry is gradually heated (Drapcho et al., 2008). The slurry is then heated to 110-120°C for 5-7 min using a jet cooker (Bothast and Schlicher, 2005). The starch polymer is broken down into short chain molecules (e.g. dextrins) by the hydrolysis of α 1-4 glucosidic bonds (Nichols and Bothast, 2008). The slurry then leaves the jet cooker and flows into a flash tank in which the temperature falls to 80-90°C. Additional α-amylase is added and the slurry is liquefied for at least 30 min (Bothast and Schlicher, 2005).
(iii) Ethanol fermentation
After liquefaction, the temperature of the mixture is decreased to 32°C and the pH is adjusted to about 4.5 (Nichols and Bothast, 2008). Glucoamylase is then added to the slurry to help hydrolyze dextrins into glucose and maltose (Drapcho et al., 2008). The slurry is transferred to fermenters where it is referred to as mash. Urea or ammonium sulfate is added as a nitrogen source to promote the growth of yeast. The addition of the yeast is usually carried out at the same time as glucoamylase is added, resulting in saccharification and fermentation occurring simultaneously in the tank (Bothast and Schlicher, 2005), resulting glucose hydrolyzed from dextrins by glucoamylase can be immediately fermented to ethanol and carbon dioxide by yeast.
(iv) Ethanol recovery
Following the 40-60 h fermentation process, distillation and dehydration steps are required in order to obtain a higher purity (Nichols and Bothast, 2008). The mash is first heated and ethanol is distillated to form a mixture consisting of 95% ethanol and 5% water (Drapcho et al., 2008). To acquire a higher purity of ethanol, a molecular sieve is used. A concentration of 99.5% of ethanol can be obtained after dehydration (Swain, 2003).
(v) DDGS processing
The residual mixture left after distillation is called whole stillage and exists in a solid and liquid state. Whole stillage contains the starch-free components of the grain, such as fiber, fat and protein. With further processing, whole stillage can be converted to co-products which are valuable feed ingredients for livestock. Whole stillage is usually not feasible for animals to consume directly because of its high moisture content, although it also contains a considerable amount of oil, fiber, protein and yeast cells (Drapcho et al., 2008). The solid and liquid fractions in the whole stillage are further separated by centrifugation. The supernatant, which is termed thin stillage, is partially recycled to the liquefaction process to reduce the usage of water (Kwiatkowski et al., 2006). The remaining thin stillage is condensed (moisture 35%) via evaporation to produce a syrup called condensed distillers solubles (CDS) and is then blended with the solid fraction which is called wet distillers grains to form wet distillers grains with solubles (Rausch and Belyea, 2006). Wet distillers’ grains or wet distillers’ grains with solubles can be directly fed to livestock (e.g. feedlot cattle). However, due to limited shelf-life and transportation costs, utilization is relatively limited. To solve this problem, wet distillers’ grains with solubles are dried (moisture 10-12%) to produce dried distillers grains with solubles (DDGS) (Drapcho et al., 2008).
Figure 1. Flow diagram of technique of Ethanol and DDGS Production (Erickson et al., 2005)
Nutrient composition of DDGS:
With increased capacity for bioethanol production, DDGS generation also continues to rise. Ethanol production could indirectly stimulate the livestock sector by producing a valuable new feedstuff for the market (Greenprint, 2002). Displacement of DDGS has been largely targeted at dairy and poultry industries (Rosentrater 2007). Distillers’ grains have an estimated three-fold increase in levels of chemical components such as protein, fibre, and fat when compared to the original grain due to the removal of starch during fermentation (Michelle, 2007; Klopfenstein et al., 2008). Traditionally, distillers’ grains have been viewed as a protein feed; however, in light of current production improvements, distillers’ grains are also an excellent source of dietary energy due to an increase in digestible fibre and fat content (Beliveau and McKinnon 2008). A potential complication in the use of DDGS is the fact that DDGS are unique in nutritional composition which may raise problems for nutritionists for ration formulation as DDGS cannot be simply substituted without also varying protein, energy, mineral and specific amino acid levels. Nutritional variability depends largely on the source grain, the processing plant and differences in types of yeast, fermentation and distillation efficiencies, as well as the amount of solubles blended back into the grain (Tjardes and Wright, 2002). Apart from this, other factors like selection of grains, duration and temperature of drying also affects the composition (Spiehs et. al., 2002). DDGS share the inferior amino acid profile (Spiehs et al., 2002). An improper amino acid balance in relation to overall crude protein will lead to inefficient energy usage, and thus decreased growth performance, and so the use of synthetic amino acids and the control of crude protein levels are necessary with the use of DDGS. Crude fiber and crude fat values are relatively high with DDGS (Shurson et al., 2004). High crude fat level means that DDGS have a similar energy value in comparison to original grain. DDGS are also beneficial in the form of phosphorus availability.
Table 1. Nutritional profile of various sources of DDGS
Feed DM (%) CP (%) Fat (%) Fibre (%) Ash (%) References
Corn 93.0 29.8 9.0 – – NRC, 1998
88.3 27.5 10.0 5.7 3.97 Noll et al., 2003
88.90 26.85 9.69 7.82 5.15 Spiehs et al., 2002
87 27 10.0 – 4.50 Lumpkins et al., 2004
86.0 30.0 9.80 5.34 3.90 Lumkins and Batal, 2005
88.2 30.3 12.8 7.0 4.8 Widyaratne, 2005
86.0 27 8.8 6.6 4.4 Batal and Dale, 2006
89.91 26.05 9.88 6.34 4.39 Fiene et al., 2006
89.36 26.45 10.08 6.99 – Waldroup et al., 2007
90.12 27.92 6.47 9.42 – Wang et al., 2007a
– 30.60 10.70 – – Michelle, 2007
Wheat 91.9 44.5 2.9 7.6 5.3 Widyaratne, 2005
94.4 40.7 4.3 – Beliveau and McKinnon 2008
91.68 38.48 4.63 6.00 5.28 USGC, 2012
Barley 87.5 28.7 – – Beliveau and McKinnon 2008
Rice 90.57 60.92 4.68 0.90 8.85 Pakhira, M.C., 2009
92.44 61.41 2.24 5.71 6.09 Ranjan, A., 2013
Triticale 90.3 31.5 6.5 – 4.2 Liu, B., 2012
DDGS as a supplemental protein source:
Protein supplements are considered ideal for low quality forages, as the crude protein provides nitrogen for maintenance and growth of rumen microbial populations, optimizing rumen health and function and promoting fibre digestion (Mathis et al., 1999). Distiller’s grains are fermentation byproducts from the distilling industry used as protein supplement in dairy rations for decades (Klopfenstein et al., 2008). Generally, Rice-based DDGS have higher CP content (64.27%) than wheat (44.5 %), Triticale (31.3%), barley (28.70%) and corn-based (27.92%) DDGS (Table 1.). The level of nitrogen (N) necessary to maintain microbial populations and optimize rumen function is 6 to 9% CP (Mathis et al. 1999). Although the level of CP serves as a benchmark, protein availability within the rumen is more critical in ruminant nutrition.
DDGS as feed supplement for poultry:
Dried distillers grains feed products are not new to the poultry industry. The first record of the actual use of distiller’s dried grains in poultry diets was by Allman and Branion (1938) who demonstrated that this feed ingredient was economical and improved chick performance and feathering, when compared to a diet containing 5% alfalfa, fish meal, and buttermilk. D’Ercole (1939) mixed DDS with DDG to produce distiller’s dried grains with solubles (DDGS) and reported that DDGS incorporated into a standard broiler diet would provide adequate nutrients to support optimal growth performance. Distillers dried grains with solubles have been regarded as good sources of energy, water-soluble vitamins, minerals and protein for poultry diets (Wang et al., 2007a) despite known deficiencies of particular amino acids and sometimes an abundance of fiber. On a protein basis, distillers’ feeds are deficient in the same amino acids as their original grains. Corn DDGS is an excellent feed ingredient for use in layer, broiler, duck and turkey diets and contains approximately 85% of the energy value in corn, has moderate levels of protein and essential amino acids and is high in available phosphorus. DDGS is an acceptable ingredient for use in poultry diets and can be safely added at levels of 5-8% in starter diets for broilers, 12-15% in grower-finisher diets for broilers, and laying hens (Swiatkiewicz and Korelski, 2008) as a partial substitute for the corn and soybean meal, currently being fed.
DDGS in broilers diet:
Researchers have consistently observed performance and meat quality of broiler chickens when DDGS in broiler diets. Previous result showed that weight gain of broilers was increased when low levels of DDGS (2.5 and 5%) were added to the diet compared to broilers fed the control diet (Day et al., 1972). Later, Waldroup et al. (1981) demonstrated that DDGS can be added to broiler diets at levels up to 25% to achieve good performance if dietary energy level is held constant. Recently, Oryschak et al. (2010) study a comparative feeding value of extruded and non extruded wheat and corn distillers dried grains with solubles at 0, 5, or 10% level for broilers and compared the growth performance and found that there was no adverse effect of including corn or wheat DDGS at up to 10% of the diet on breast meat weight, or yield. However, Wang et al. (2007a) conducted an experiment to evaluate different levels of “new generation” distillers dried grains with solubles (DDGS) in broiler diets and found that good quality DDGS could be used in broiler diets at levels of 15 to 20% with little adverse effect on live performance but might result in some loss of dressing percentage or breast meat yield.
DDGS in chicken layers diet:
Recent research studies have shown that 10% DDGS can be added to layer diets, increased egg production, lower egg weight and feed conversion per egg laid (Krawczyk et al., 2012). However, feeding 15% DDGS in diet did not affect egg production, egg weight, feed consumption, or feed utilization (Lumpkins et al., 2005) but at even higher dietary inclusion rates as during laying had no negative effects on egg production, specific gravity production and haugh units (Ghazalah et al., 2011). Benabdeljelil and Jensen (1989) reported that feeding diets containing DDGS resulted in an improvement in haugh units, but it was not a consistent response. However, Ghazalah et al. (2011a) found that egg production, egg weight and egg mass of laying hens were decreased as dietary inclusion of DDGS increased.
Physical and chemical properties of DDGS:
Physical and chemical properties of DDGS vary among sources and can influence its feeding value, handling, and storage characteristics. These include color, smell, particle size, bulk density, pH, color, thermal properties, flowability, shelf life stability, and hygroscopicity. Distiller’s dried grains with solubles are characterized as a heterogeneous granular material consisting of a range of particle types, sizes and shapes. Particles included corn fragments (i.e. tip cap, and pericarp tissues), non-uniformly crystallized soluble protein and lipid coatings on the surface of these fragments, and agglomerates (i.e. “syrup balls”) that are formed during the drying process (Rosentrater, 2012). These characteristics affect handling, flowability, and storage behavior of DDGS.
A. Color
Color of corn DDGS can vary from very light, golden yellow in color to dark brown in color. This depend upon several factors which is the amount of solubles added to grains before drying, type of dryer and drying temperature used and the natural color of the feedstock grain being used. The color of corn kernels can vary among varieties and has some influence on final DDGS color. Corn-sorghum blends of DDGS are also somewhat darker in color than corn DDGS because of the bronze color of many sorghum varieties. When a relatively high proportion of solubles are added to the mash (grains fraction) to make DDGS, the color becomes darker. Browning or blackening of DDGS can indicate excessive heat treatment or spoilage due to improper storage, thus reducing nutritive value.
B. Smell and pH
High quality and golden colour DDGS has a sweet fermented smell but poor quality may result in burn and smoky smell (Cromwell et al., 1993) which may an indication of overheating. For certain species of animals, smell may influence palatability or intake. Piglets and calves are sensitive to olfactory properties and affect the intake and finally the growth rate of animals. Inclusion of sour smelling DDGS at large quantities in the formulation may also affect the smell of final feed. It is possible that sour smell may be related to pH. The pH of DDGS sources vary in the range 3.6-5.0 with averages 4.1. In general, the low pH of DDGS may be useful as it may prevent harmful bacteria to grow (Tangendjaja, B., 2007).
C. Particle size
Particle size and particle size uniformity of feed ingredients are important considerations for livestock and poultry nutritionists when selecting sources and determining the need for further processing when manufacturing complete feeds or feed supplements. Particle size affects nutrient digestibility, mixing efficiency, amount of ingredient segregation during transport and handling, pellet quality, bulk density, palatability and sorting of meal or mash diets.
D. Flowability
Flowability is defined as the ability of granular solids and powders to flow during discharge from transportation or storage containments. Flowability is not an inherent natural material property, but rather a consequence of several interacting properties that simultaneously influence material flow (Rosentrater, 2006). Flowability problems may arise from a number of synergistically interacting factors including product moisture, particle size distribution, storage temperature, relative humidity, time, compaction pressure distribution within the product mass, vibrations during transport and/or variations in the levels of these factors throughout the storage process (Rosentrater, 2006). In addition, other factors that may affect flowability include chemical constituents, protein, fat, starch, and carbohydrate levels as well as the addition of flow agents. Since flow behaviour of a feed material is multidimensional, there is no single test that completely measures the ability of a material to flow (Rosentrater, 2006). Shear testing equipment are the primary equipment used to measure the strength and flow properties of bulk materials. Another approach for measuring the flowability of granular materials involves measuring four main physical properties: angle of repose, compressibility, angle of spatula, and coefficient of uniformity (e.g. cohesion) (Rosentrater, 2006). Several recent studies have been published regarding the causes of DDGS flowability problems and potential solutions to improve flowability. Ganesan et al. (2008a) suggested that DDGS flowability may be affected by storage moisture, temperature, relative humidity, particle size, time or temperature variations, and other factors. Bhadra et al. (2008) evaluated surface characteristics and flowability of DDGS using cross sectional staining of DDGS particles and showed that a higher amount of protein thickness compared to carbohydrate thickness in surface layers from DDGS had lower flow function index, and greater cohesiveness, which indicates possible flow problems. They also observed that higher surface fat occurred in samples with worse flow problems. Ganesan et al. (2008b) then conducted a study to determine the effect of moisture content and solubles level on the physical, chemical, and flow properties of DDGS. They determined the effect of five moisture levels (10, 15, 20, 25, and 30%) on the resulting physical and chemical properties of DDGS containing 4 levels of solubles (10, 15, 20, and 25%). Results from this study showed that the level of solubles and moisture content had significant effects on physical and flow properties (e.g., aerated bulk density, packed bulk density and compressibility). The dispersibility, flowability index, and floodability index were used to show that flowability generally declined as moisture content increased for most of the soluble levels evaluated. The color and protein content of the DDGS were also affected as soluble levels increased. In attempts to improve DDGS flowability, two studies have been conducted to determine the effects of adding selected flow agents to DDGS on flowability (Johnston et al., 2009). Ganesan et al. (2008a) evaluated the effect of 0, 1, and 2% calcium carbonate addition to DDGS with variable moisture content and soluble levels. Flowability of DDGS was reduced when percentage of solubles and moisture content increased. Adding the flow agent (CaCO3) did not improve the flow properties of DDGS, which may have been due to the lack of surface affinity between DDGS and the flow agent particles, or too little inclusion of the flow agent.
E. Storage stability
i. Moisture
It is well accepted in the grain handling and feed industry that moisture content of grain and grain by-products should be less than 15% to prevent heating and spoilage (i.e. molds and mycotoxins). Therefore the moisture content of DDGS is usually between 10 to 12%, there is minimal risk of spoilage during transit and storage.
ii. Fat oxidation
Crude fat content of corn DDGS range from 5 to 12%. Vegetable oils, like corn oil are high in unsaturated fatty acids. As a result, vegetable oils have a higher unsaturated to saturated fatty acid ratio (U:S) compared to animal fats. The U:S ratio affects the melting point and energy value of fat, as well as the fatty acid composition in liver, fat, and meat of poultry. The iodine value is a method of estimating U:S ratio. Each double bond in a fatty acid has the capability of taking up two atoms of iodine. By reacting fatty acids with iodine, it is possible to determine the degree of unsaturation of a fat or oil. The iodine value is defined as grams of iodine absorbed by 100 grams of fat. Because unsaturated fats have more double bonds, they will have higher iodine values than saturated fats. Iodine value can be used to estimate fatty acid profiles of various fat sources. Fats are susceptible to breakdown by oxidation to form peroxides, which are unstable compounds, and can become rancid. Peroxide value is sometimes also referred to as initial peroxide value because it is determined on a sample as submitted. A peroxide value of 5.0 mEq of peroxide/kg or lower is an indication of little or no rancidity. High free fatty acid content may indicate oxidation or breakdown of the fat and potential rancidity. Free fatty acids are those that are not linked to glycerol by an ester linkage, but are in free form. Oxidation of fat produces free fatty acids as a by-product. Moisture in fats and high fat ingredients may increase rancidity. However, this is of relatively little concern in DDGS because the moisture content is typically only 10 to 11%.
Economics of DDGS in poultry feeding rations:
DDGS is a very unique mid-protein, high-energy excellent and economically feasible alternative feed ingredient (Hung, 2008). One of the biggest factors for determining whether DDGS is an economical poultry feed ingredient because it replace a larger proportion of corn and soybean meal in feeds (i.e. higher dietary DDGS inclusion rates).
Impact of DDGS on environment and human health concerns
Because manure excretion of nitrogen, phosphorus, and sulfur is a function of dietary levels (Morse et al., 1992), there are a number of environmental concerns when feeding high levels of distillers’ grains (>40% of the diet; Hao et al., 2009). Excess environmental nitrogen can contaminate water and air with nitrate or ammonia via leaching or nitrous oxide via denitrification, respectively (McGechan and Topp, 2004). High levels of phosphorus in manure increases the amount of land necessary for manure application, and as well as increasing the potential for run-off and eutrophication (Spiehs and Varel, 2009). Likewise, high excretion of sulfur can increase hydrogen sulfide (H2S) emissions from livestock operations, thereby negatively impacting air quality (Spiehs and Varel, 2009). It has been indicated that high levels of DDGS in the diet can increase the concentration of isobutyric, valeric, and isovaleric acids, volatile fatty acids (VFA) linked to odour emissions (Hao et al., 2009).
Conclusion
The demand of soybean, maize and other grains in the global market is ever increasing, causing a sharp increase in price, making the situation of the feed industries even worse. Thus DDGS has the ample opportunity to be utilized as an alternative grain resource in feed industries because DDGS are highly nutritious, economical and cost effective feed resources which reducing feeding cost as well as having higher feeding values than other original grain. DDGS is a good dietary source of energy, protein, water-soluble vitamins and minerals for poultry so additional protein or amino acid supplementation can be used to improve productivity.
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