By Jerry Shurson, University of Minnesota Department of Animal Science
Compared to other feed ingredients, dried distillers grain with solubles has some unique physical and chemical characteristics that affect its storage and handling characteristics. The use of DDGS in animal feeds has created challenges for handling and unloading from rail cars, containers and bulk vessels, especially during humid summer months. There are also challenges with transport using conventional feeder screws, as well as flowability and discharge from feed silos and storage bins at commercial feed mills.
Proper feed ingredient storage is essential for preserving nutritional value and preventing spoilage. The original condition of a feed ingredient is the most important factor affecting preservation of quality during storage, and is influenced by moisture content, relative humidity and temperature (Mills, 1989). Moisture within a feed ingredient ultimately reaches equilibrium with the air within and between particles over time, and depending on the conditions, may lead to the growth of molds and other deleterious microorganisms (Mills, 1989). However, maximum acceptable moisture concentrations of grains have been established, but vary among types of grains and length of storage period (Mills, 1989).
Furthermore, maximum relative humidity levels have been established to prevent mold growth (<70%), bacteria growth (<90%), and storage insects (<60%; Mills, 1989) of grains. However, it is important to remember that moisture and relative humidity interact with temperature in the storage environment. High temperatures of grain and feed ingredients at the time of loading a storage bin can be maintained for many months if the mass is aerated. Temperature and moisture content determine the extent of enzymatic and biological activities of grains and other ingredients, and temperature differences within the stored mass can increase the risk of mold growth through moisture migration (Mills, 1989). Unfortunately, no studies have been conducted to determine optimal storage conditions to maintain DDGS quality and prevent spoilage over extended storage periods of time or under various climatic conditions. As a result, it is generally assumed that drying DDGS to a moisture content <12% is acceptable to minimize the risk of spoilage when stored under moderate temperatures and humidity.
Storage bin space allocation
When a new feed ingredient is used for the first time in a commercial feed mill, appropriate storage space must be made available or constructed because it is unusual that a feed mill would have an open bin or unused storage space to accommodate a new ingredient. While a simple solution is to decide to discontinue using an existing ingredient and designate that storage bin for the new ingredient, it is very difficult to do this without disrupting the feed manufacturing process (Behnke, 2007). If the bin volume, hopper configuration, and feeder screw design are not suitable for the new ingredient, exploring other options are necessary (Behnke, 2007). When deciding feed ingredient allocation to storage bins, one of the most important considerations is determining the expected diet inclusion rates that will be used in all feeds manufactured so that daily or monthly usage rate and frequency of use can be calculated (Behnke, 2007). Perhaps the second most important consideration is related to the physical properties, such as bulk density and flow characteristics, of the ingredient.
Bridging, caking and flowability of DDGS
One of the greatest challenges for handling DDGS is its propensity for bridging, caking and causing poor flowability when attempting to unload it from rail cars, containers and bulk vessels. Flowability is defined as “the relative movement of a bulk of particles among neighboring particles or along the container wall surface” (Pelig, 1977). Unfortunately, some DDGS sources have poor flowability and handling characteristics (Bhadra et al., 2008), which has prevented routine use of rail cars for transport, and has led to the development of specially designed unloading equipment for bulk vessels and containers. Poor flowability has been a key factor that has limited its use in livestock and poultry diets because of bridging in bulk storage containers.
Many factors affect the flow of a bulk ingredient (Peleg, 1977), and no single measurement adequately describes flowability (Bhadra et al., 2008). However, while moisture content of DDGS, and the relative humidity of the environment, are the major contributing factors to bridging, caking and poor flowability, other factors such as particle size, proportion of condensed solubles added to the grains fraction before drying, dryer temperature, moisture content at dryer exit, and others have also been attributed to this problem (Ganesan et al., 2008a,b,c). Moisture content of DDGS is generally between 10% to 12% to avoid spoilage due to mold growth during long-term storage. However, DDGS is also hygroscopic and can gradually increase in moisture content during exposure to humid conditions over a long storage period (Ganesan et al., 2007). The hygroscopic properties of DDGS can lead to bridging, caking and reduced flowability during transport and storage (Rosentrater, 2007).
Because there is limited storage capacity for DDGS at ethanol plants, it is sometimes loaded into transport vessels within a few hours after it exits the dryer before moisture equilibrates. When this occurs, DDGS will harden and become a solid mass in trucks, rail cars and containers, making it difficult to unload. However, if warm DDGS is allowed to cool so that the moisture can equilibrate before loading, flowability is greatly improved. Currently, most ethanol plants have implemented a minimum 24-hour “curing,” or moisture equilibration period before loading to avoid bridging and caking to prevent damage and repair cost to rail cars resulting in attempts to dislodge it while unloading. Ideally, holding DDGS for five to seven days is considered to be ideal for allowing complete moisture equilibration to occur so that the liquid bridges formed in the cooled mass can be broken, which minimized further handling difficulties (Behnke, 2007).
Unfortunately, the majority of ethanol plants have only about two to three days of storage capacity during continuous operations, resulting in an inability to provide a five- to seven-day period for adequate moisture equilibration.
The equilibrium relationship between moisture content and relative humidity of the surrounding environment for bulk solids is affected by sorption isotherms that indicate the corresponding water content at a specific, constant temperature at a specific humidity level. Therefore, as the relative humidity in the storage environment increases, the sorption increases and causes formation of liquid bridges between particles (Mathlouthi and Roge, 2003). Adsorption (ability to hold water on the outside or inside surface of a material) and desorption (release of water through or from a surface) of moisture under humid conditions is complex and is affected by the carbohydrate, sugar, protein, fiber and mineral concentrations of a feed ingredient (Chen, 2000). Understanding this relationship for DDGS is important for determining the critical moisture and relative humidity levels that may cause bridging and caking of DDGS during transport and storage.
Kingsly and Ileleji (2009) showed that formation of liquid bridges occurred in DDGS when the relative humidity reached 60%. At 80% relative humidity, DDGS reached maximum moisture saturation, and at 100% relative humidity, the liquid bridge formed by adsorption of moisture hardened and led to the formation of a solid bridge as humidity was reduced. These results indicate that increased relative humidity during transport and storage causes irreversible bridging between DDGS particles and leads to particle aggregation (clumping), caking and reduced flowability.
Pelleting DDGS is another approach that a few ethanol plants have attempted to use to improve bulk density and flowability. Research at Kansas State University evaluated the use of various conditioning temperatures and pellet die sizes on ease of pelleting, physical properties and flow characteristics of DDGS, and results showed that almost any combination of pelleting conditions improved flowability of DDGS (Behnke, 2007).
However, this approach has not been implemented in the U.S. ethanol industry for several reasons. First, it would require additional cost for existing ethanol plants because of the need to purchase, install and operate expensive boilers and pellet mills; would require additional personnel training and labor cost; and would require additional storage space. Furthermore, some DDGS customers may be reluctant to purchase pelleted DDGS because it may be perceived to be adulterated with other “fillers,” it may have reduced amino acid and nutrient digestibility due to thermal treatment during the pelleting process, and because of the added cost of re-grinding DDGS pellets before adding it to other ingredients when manufacturing complete feeds.
Installments in the DDGS series
Part 12: DDGS present handling and storage considerations
Effects of oil content of DDGS on flowability
Physical properties of conventional high-oil (Rosentrater, 2006), reduced-oil (Ganesan et al. 2009), and low-oil (Saunders and Rosentrater, 2007) DDGS have been evaluated. Ganesan et al. (2009) showed that reduced-oil DDGS may have improved flow properties compared to conventional high-oil DDGS, but both types were classified to have “cohesive” properties. This suggests that regardless of oil content, DDGS is prone to bridging and caking problems during long-term storage. Furthermore, these researchers suggested that chemical composition and particle surface morphology (roughness, size and shape) may have a greater effect of DDGS flowability than oil content.
As previously discussed, extended storage time for more complete moisture equilibration and pelleting DDGS are currently not viable options for preventing handling and flowability challenges. Therefore, several new unloading equipment designs have been developed and are being used to facilitate discharge of DDGS from rail cars and containers. For example, stationary devices that are located above a rail car pit, use a steel spear to break the hardened mass before unloading. Although these methods reduce the time required for unloading, they also increase labor and equipment cost. Furthermore, many commercial feed mills have chosen to use flat storage rather than bin or silo storage of DDGS to avoid flowability and transfer problems. The main advantages of flat storage are that it minimizes flowability problems and requires less short-term capital investment compared with constructing silos. However, use of flat storage requires more labor, front-end loading equipment to move the material, increases the risk of contamination with other ingredients within the storage facility and increases “shrink” losses.
Effects of additives on DDGS flowability
The addition of various flow agents has been another approach that has been attempted to improve flowability of DDGS, but only a few studies have been conducted to evaluate their effectiveness. Ganesan et al. (2008a) evaluated the effects of adding calcium carbonate to DDGS with variable moisture and condensed distillers solubles content in a laboratory setting, and showed no benefits for improving flowability. Johnston et al. (2009) evaluated flowability after adding 2.5 kilograms per metric ton of a product from Delst Inc., Temecula, Calif.; 2% calcium carbonate from ILC Resources Inc., Des Moines, Iowa; or 1.25% clinoptilolite zeolite from St. Cloud Mining Co., Winston, N.M. to DDGS containing either 9% or 12% moisture. After flow agents were added and mixed with DDGS at the ethanol plant, trucks were loaded, traveled 250 kilometers, were parked and motionless for 60 hours, then travelled an additional 250 kilometers back to the ethanol plant where it was unloaded, and flowability measurements were obtained. Outdoor temperatures on each of the four days (over a two-month period) during this study ranged from 12.9 degrees C to 27.8 degrees C, and outdoor relative humidity ranged from 34% to 67%. Average particle size of the DDGS source ranged from 584 to 668 micrometers. The flow rate during unloading of each truckload of DDGS was improved by adding zeolite (558 kilograms per minute) compared with the product from Delst Inc. (441 kilograms per minute), but these treatments were not different from the control (no flow agent; 509 kilograms per minute) and the calcium carbonate (512 kilograms per minute) treated DDGS loads. Furthermore, flowability score (1 = free flowing, 10 = badly bridged) was improved when zeolite was added to DDGS (4.0) compared with the control (6.0), the Delst Inc. product (6.5) and calcium carbonate (5.5). Moisture content at the time of loading was the most important predictor (explained 70% of the variation) of flow rate of DDGS, where each 1% increase in moisture content from 9%, decreased unloading rate by 100 kilograms per minute. Similar results were reported by Ganesan et al. (2008b) where increasing moisture content of DDGS reduced flowability. Ganesan et al. (2008b) also reported that as the Hunter b* score (yellowness of color) increased in DDGS, flow rate also increased, but this only accounted for 4% of the variation in flow rate. These results indicate that the most effective criteria from improving flow rate in DDGS is to dry it to less than 10% moisture content, while adding the Delst Inc. product, calcium carbonate or zeolite provided no benefits for improving flowability of DDGS during unloading from trucks.
Effects of bulk density of DDGS on freight weight and particle segregation
Maintaining consistent bulk density of DDGS when loading rail cars and containers has been a challenge for both marketers and buyers because of the desire to achieve consistent freight weights in sequentially loaded rail cars and containers to minimize shipping costs (Ileleji and Rosentrater, 2008). Bulk density varies among DDGS sources, and has been reported to range from 391 to 496 kg/m3 (Rosentrater, 2006) and from 490 to 590 kg/m3 (Bhadra et al., 2009). Clementson and Ileleji (2010) suggested that differences in bulk density observed during loading of rail cars may be due to particle segregation. This is likely to occur because DDGS is a granular bulk solid with particles of various sizes, densities and morphological characteristics found in the structural components of corn grain (Ileleji et al., 2007). Particle segregation was shown to occur during handling and gravity discharge of DDGS (Ileleji et al., 2007; Clementson et al., 2009). Clementson and Ileleji (2010) conducted a study to evaluate bulk density variation of DDGS when filling and emptying hoppers to simulate loading of rail cars at an ethanol plant, and showed that the variation in bulk density that occurred as DDGS was loaded and emptied was mainly attributed to particle segregation. These researchers showed that after filling, the finer, smaller and denser particles were concentrated in the center of the hopper, while the larger, coarser and less-dense particles were concentrated on the sides of the hopper. This phenomenon not only causes variation in bulk density during transloading of DDGS, but it should also be considered when sampling DDGS for nutrient analysis because the location of sampling can influence the mixture of segregated particles and ultimately affect the analytical results (Clementson et al., 2009).
Effect of storage bin design and particle size on flowability of DDGS diets
Feed storage bin design
Flowability of DDGS is not only a challenge during loading, transport, storage and feed manufacturing, but it can also create challenges on swine farms when DDGS diets are fed in meal form. Suboptimal feed flow can reduce the rate of feed delivery to feeders, as well as bridge in feeders leading to out-of-feed events that can increase stress and the likelihood of gut health problems and reduced growth performance in pigs (Hilbrands et al., 2016). This problem is a greater concern when there is an economic incentive to increase diet inclusion rates of DDGS to 30% or more in swine diets, especially when meal diets with small particle size are fed to improve feed conversion of pigs. Storage bin design can be a significant cause or a potential solution to the flowability problems with feed containing DDGS.
Hilbrands et al. (2016) conducted a study to evaluate feed flow from three commercially available feed storage bins. The three bin designs consisted of: 1) a galvanized steel, smooth-sided, seamless bin with a 60-degree round discharge cone (Steel60), 2) a galvanized, corrugated steel bin with a 67-degree round discharge cone (Steel67), and 3) a white, polyethylene bin with a 60-degree round discharge cone (Poly60). The bin styles were chosen to represent differences in slopes of the sides of discharge cones, as well as different construction materials in the bin walls. Diets used in this study contained 55% corn, 35% soybean meal, 40% DDGS and 2% minerals and vitamins, and were ground to an average particle size ranging from 736 to 1,015 microns. The study was conducted in two experiments during the summer and fall. During the summer, daily high and low temperatures ranged from 30.9 degrees C to 16.6 degrees C, and daily relative humidity ranged from 39.4% to 100%. During the fall, daily high and low temperatures ranged from 2.9 degrees C to 23.7 degrees C, and daily relative humidity ranged from 23.3% to 92.7%.
Feed flow rate out of bins was faster from Poly60 bins compared with Steel60 bins, with discharge rate from Steel67 bins being intermediate (Table 1). However, it was interesting that although the Steel60 bins that had the slowest flow rate, they required the fewest number of taps on bins to keep feed flowing during discharge. As shown in Table 2, the presence of a passive agitator increased feed flow rate among all bin designs compared with bins without agitators, but the presence of agitators in Poly60 bins resulted in greater feed flow rate than the presence of agitators in steel bins. However, unlike results in Experiment 1, there was no difference in the number of taps required to establish feed flow among the six bin design combinations.
These results indicate that feed bin design affects the flow rate during discharge of meal diets containing 40% DDGS. The Poly60 bin provided that best feed flow and highest discharge rates compared with the steel bin designs evaluated, and installing passive agitators increase feed flow in all bin designs.
Particle size among DDGS sources is highly variable, with an average of 660 µm and a standard deviation of 440 µm (Liu, 2008). Particle size of DDGS not only contributes to its flow properties (Ganesan et al., 2008a,b,c), but also affects metabolizable energy content and nutrient digestibility (Mendoza et al., 2010). To further evaluate the effects of DDGS particle size on ME content and nutrient digestibility for growing pigs, Liu et al. (2012) determined the ME content and nutrient digestibility of the same source of DDGS ground to three particle sizes (818 µm = coarse, 594 µm = medium and 308 µm = fine). These researchers also evaluated flowability of diets containing 30% DDGS. As expected, ME content of DDGS improved as the particle size was reduced, where each 25 µm reduction in average particle size (between 818 and 308 µm) increased the ME content of the diet by 13.5 kilocalories per kilogram of dry matter. However, there were no effects of DDGS particle size on nitrogen and phosphorus digestibility. Diet flowability was reduced in the 30% DDGS diets compared with the control corn-soybean meal diet, and was lowest in the diet containing finely ground DDGS (determined by measuring the drained angle of repose). When flowability of these diets was determined using poured angle of repose as the measurement criteria, there were no differences in flowability between the control and 30% DDGS diets, nor were there differences among diets containing different particles sizes of DDGS.
Minimizing mold growth and mycotoxin production during storage
Toxigenic fungal species of molds can develop on grains while growing in fields before harvest, as well as during storage after harvest (Suleiman et al., 2013). Consequently, fungal species are often classified as field fungi or storage fungi (Barney et al., 1995). Field fungi can infect corn grains and produce mycotoxins before harvest at moisture content between 22% to 33%, relative humidity greater than 80%, and over a wide range of temperatures (10 degrees C to 35 degrees C; Williams and MacDonald, 1983; Montross et al., 1999). Most field fungi do not survive during storage, but some species can continue to grow under appropriate storage conditions (Sanchis et al., 1982). Storage fungi also originate from the field and can replace field molds that infected corn grain prior to harvest (Reed et al., 2007). As shown in Table 3, storage fungi require a relative humidity that is greater than 70%, and moisture content greater than 12% for corn grain (Montross et al., 1999). Additional fungal species may also be introduced after harvest and include Fusarium spp., Rhizopus spp. and Tilletia spp. (Williams and MacDonald, 1983; Barney et al., 1995). Because DDGS is produced from corn grain, it is reasonable to assume that these same molds may be present in DDGS. However, due to the unique physical and chemical properties of DDGS, it is unknown if these relative humidity and moisture conditions apply similarly as for corn grain. In fact, DDGS may be more susceptible to mold growth than corn grain because mechanical damage of corn grain during and after harvest can provide entry for fungal spores (Dharmaputra et al., 1994), and broken corn kernels and foreign material promote growth of storage molds (Sone, 2001).
Effects of feeding oxidized lipids to pigs
Corn DDGS contains the one of the highest lipid concentrations of most common feed ingredients used in animal feeds around the world. Lipid oxidation is a complex chemical chain reaction induced by heat, oxygen, moisture and transition metals (e.g. copper and iron), where free-radicals are converted to toxic aldehydes and other oxidation compounds (Shurson et al., 2015). Corn oil present in DDGS consists primarily of polyunsaturated fatty acids, particularly linoleic acid (C18:2, 58%), which is highly susceptible to oxidation (Frankel et al., 1984). When lipids are heated at relatively high temperatures, large quantities of secondary lipid oxidation products are produced including aldehydes, carbonyls and ketones (Esterbauer et al., 1991). Drying temperatures used to produce DDGS can be as high as 500 degrees C, which makes the oil in DDGS susceptible to lipid oxidation. All of the pro-oxidation conditions (heat, oxygen, moisture and transition minerals) are present in ethanol plants that produce DDGS, and DDGS may be further exposed to these factors during transport, storage and manufacturing of complete feeds in commercial feed mills. Therefore, there is some concern about the extent of oxidation in DDGS and its effects on pig growth performance and health.
Feeding oxidized lipids to pigs and broilers has been shown to reduce growth performance and increase oxidative stress. Hung et al. (2017) conducted a meta-analysis using swine and poultry data from 29 publications that showed an average reduction in average daily gain (5%), average daily feed intake (3%), Gain:Feed (2%), and serum of plasma vitamin E (52%), while increasing serum thiobarbituric acid reactive substances (120%) across all studies. Recent reviews by Kerr et al. (2015) and Shurson et al. (2015) provide a comprehensive summary of biological effects of feeding oxidized lipids to swine and poultry, along with the challenges of measuring oxidation of lipids and interpreting the results. As a result, some swine feeding trials (Song et al., 2013; Song et al., 2014; Hanson et al., 2015a) have shown inconsistent growth performance responses from feeding a highly oxidized DDGS diets to pigs.
Lipid oxidation among DDGS sources
Song and Shurson (2013) evaluated measures of lipid oxidation and color of 31 corn DDGS sources obtained from ethanol plants in nine states in the United States, and compared these values with a sample of corn as a reference (Table 4). Peroxide value and TBARS are two common measures of lipid peroxidation that have been used in the feed industry for many years. However, these oxidation indicators have several limitations like all other measures of oxidation, and therefore, are not always reflective of the true extent of oxidation of lipids (Hung et al., 2017; Shurson et al., 2015). Currently, there are no standards or guidelines for measuring lipid oxidation in feed ingredients. However, Wang et al. (2016) suggested that 4-hydroxynonenal and a ratio of select aldehydes provide better estimates of the actual extent of oxidation in vegetable oils. Unfortunately, these analytical procedures are not commonly used in commercial laboratories.
Peroxide value is used to estimate the extent of peroxidation during the initiation phase of the oxidation process. The PV of the DDGS samples was highly variable (CV = 97.5%), with a minimum value of 4.2 and maximum value of 84.1 meq/kg oil. The TBARS value is used as an estimate of the extent of lipid oxidation during the propagation phase of oxidation, which is when the majority of aldehydes are produced. There was less variability (CV = 43.6%) in TBARS values among DDGS sources compared with PV values, and ranged from 1.0 to 5.2 ng MDA equiv./mg oil. Both PV and TBARS were greater in DDGS samples compared with the corn reference values. This was expected because of the thermal processing involved in producing DDGS. Moderate negative correlations were observed for colorometric measures between L* and PV (r = -0.63) and b* and PV (r = - 0.57), with slightly greater negative correlations between L* and TBARS (r = -0.73) and b* and TBARS (r = -0.67). These results suggest that darker-colored and less-yellow-colored DDGS samples may be more oxidized. However, color of DDGS is affected by many factors and should not be used as a definitive measure of the extent of corn oil oxidation in DDGS.
However, subsequent studies involving the most oxidized DDGS source to wean-finish pigs (Song et al., 2014), and sows and their offspring through the nursery phase (Hanson et al., 2016) had no detrimental effects on growth performance. The lack of growth performance responses in these studies may have been a result of the naturally high concentrations of antioxidant compounds (tocopherols, ferulic acid, lutein, zeaxanthin; Shurson, 2017) present in DDGS, and conversion of sulfur compounds into endogenous antioxidants.
Use of commercial antioxidants to minimize lipid oxidation
Synthetic antioxidants are commercially available and are used to minimize oxidation in feed fats and oils (Valenzuela et al., 2002; Chen et al., 2014). The most commonly used synthetic antioxidants include t-butyl-4-hydroxyanisole (BHA), 2,6-di-t-butylhydroxytoluene (BHT), t-butylhydroquinone (TBHQ), ethoxyquin, and 2,6-di-ter-butyl-4-hydroxymethyl-phenol (Guo, et al., 2006).
Only one study has been published to evaluate the effectiveness of adding synthetic antioxidants to high-oil (13% crude fat) and low-oil (5% crude fat) DDGS (Hanson et al., 2015b). Samples of these two DDGS sources contained either no added synthetic antioxidants (control), or 1,000 mg/kg TBHQ (Kemin Industries, Des Moines, Iowa), or 1,500 mg/kg of ethoxyquin and TBHQ (Novus International, St. Louis, Mo.). After antioxidants were added, samples were stored at 38 degrees C and relative humidity of 90% in a controlled environmental chamber for 28 days. Subsamples were collected on Day 0, 14 and 28 to determine the extent of lipid oxidation at each time point. Results of this study showed that significant lipid oxidation occurred under these storage conditions (Table 5). Oxidation increased during the 28-day storage period and the extent of oxidation was greatest in the high-oil DDGS source compared with the low-oil DDGS source. However, the addition of either the Kemin or the Novus product to either the high- or low-oil DDGS sources reduced oxidation by about 50%. Therefore, these results show that the addition of either two commercially available antioxidants are effective in reducing lipid oxidation in DDGS when stored up to 28 days in hot, humid conditions. In addition, moisture content of DDGS sources increased from 10.2% to 21.4% during the 28-day storage period, which led to significant mold growth in all samples.
The physical and chemical characteristics of DDGS can cause challenges in handling and storage. Particle size among DDGS sources is highly variable (660 µm + 440 µm), which contributes to its flow properties while also affecting metabolizable energy content and nutrient digestibility. However, reducing moisture content to less than 10% appears to have the greatest effect on improving flow rate of DDGS, while the addition of flow agents (Delst Inc. product, calcium carbonate and zeolite) appear to provide no benefits. Feed bin design affects the flow rate during discharge of meal diets containing 40% DDGS, and installing passive agitators increase feed flow in all bin designs. Bulk density varies from 391 to 590 kg/m3 among DDGS sources. Particle segregation occurs during filling, where the finer, smaller and denser particles are concentrated in the center of the hopper, while the larger, coarser and less-dense particles are concentrated on the sides of the hopper. This particle distribution should also be considered when sampling DDGS for nutrient analysis because the location of sampling can influence the mixture of segregated particles and ultimately affect the analytical results.
The hygroscopic properties of DDGS cause it to accumulate moisture over time, which could encourage mold growth and mycotoxin production during extended storage periods under humid conditions. The extent of heating during the drying process used to produce DDGS can cause lipid oxidation, which may lead to reductions in pig growth performance, but studies have shown inconsistent responses. However, adding commercial antioxidants can reduce oil oxidation in DDGS during storage under high temperature and humidity conditions.
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