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INTRODUCTION
Corn milling co-products are expected to increase dramatically in supply.Two primary types of milling processes currently exist, resulting in quite different feed products.The dry milling process produces distillers grains plus solubles, and the wet milling process produces corn gluten feed. These feeds can be marketed as wet feed, or they can be dried and marketed as either dry corn gluten feed or dry distillers grains with or without solubles. For the purposes of this article, only wet corn gluten feed (WCGF) and wet distillers grains plus solubles (WDGS) will be discussed.The majority of plant expansions are dry milling plants that produce WDGS; however, an increase in supply of WCGF is also expected.Therefore, these feeds may be very attractive for beef producers to use as an energy source. This article will focus on the production, composition of these feeds, energy values, and economics of using WDGS. Some other management issues will be discussed as well including grain processing when these co-products are used in feedlot diets, roughage level when these co-products are used, and feeding combinations of WDGS and WCGF. Forage fed situations will be covered with dried co-products as this will be the most common application for both energy and protein supplementation in many forage feeding situations.
WET MILLING
Wet milling is a process that requires use of high quality (No. 2 or better) corn that results in numerous products for human use. During this process (Figure 1), corn is "steeped" and the kernel components are separated into corn bran, starch, corn gluten meal (protein), germ, and soluble components.Wet corn gluten feed usually consists of corn bran and steep, with germ meal added if the plant has those capabilities. For a more complete review of the wet milling process, the reader is referred to Blanchard (1992). Dry corn gluten feed contains less energy than wet corn gluten feed (Ham et al., 1995) when fed at high levels in finishing diets.Wet corn gluten feed can vary depending on the plant capabilities. Steep liquor contains more energy and protein than corn bran or germ meal (Scott et al., 1997).Therefore, plants that apply more steep to corn bran or germ meal will produce WCGF that is higher in CP and energy.
WCGF contains 16 to 23% CP, which is approximately 80% ruminally degradable (degradable intake protein, DIP) protein used by microbes. During wet milling, corn gluten meal is removed and marketed in higher value markets. Corn gluten meal should not be confused with WCGF, as corn gluten meal contains approximately 60% CP which is only 40% DIP or 60% bypass protein (undegradable intake protein, UIP). Distinct differences exist for WCGF, even within companies, due to plant-toplant variation. Stock et al., (1999) divided WCGF into two main categories, depending on the ratio of steep to bran. Because of differences in the amount of steep added, WCGF has approximately 101 to 115% the energy value of dry-rolled corn when fed at levels of 20 to 60% of diet DM (Stock et al., 1999). Higher energy (and protein) is associated with increases in steep added in WCGF.
DRY MILLING
In the dry milling industry, the feed product(s) that are produced are distillers grains, distillers grains + solubles, and distillers solubles. Depending on the plant and whether it is producing wet or dry feed, the relative amounts of distillers grains and distillers solubles mixed together varies. However, our current estimates are that wet distillers grains + solubles are approximately 65% distillers grains and 35% distillers solubles (DM basis). Distillers grains (+ solubles) will hereby be referred to as either WDGS (wet distillers grains) or DDGS (dry distillers grains). Our assumption is that the distillers grains will contain some solubles, but this can vary from plant to plant.The dry milling ethanol process (Figure 2) is relatively simple where corn (or another starch source) is ground, fermented, and the starch converted to ethanol and CO2.Approximately 1/3 of the DM remains as the feed product following starch fermentation assuming that starch source is approximately 2/3 starch. As a result, all the nutrients are concentrated 3-fold because most grains contain approximately 2/3 starch. For example, if corn is 4% oil, the WDGS or DDGS will contain approximately 12% oil.The wet milling industry is more complex and the corn kernel is divided into more components for higher value marketing. For example, the oil is extracted and sold in the wet milling industry as is the corn gluten meal, a protein supplement that contains a large amount of bypass protein, or UIP, commonly marketed to the dairy, poultry, or pet industries. The importance of understanding the process is that the resulting feed products from these two industries are quite different based on how they are produced.
The majority of the research on distillers grains as an energy source has been conducted on finishing cattle. Feeding wet distillers grains (WDGS) results in better performance than dry distillers grains (DDGS;Table 1).
Experiments evaluating the use of wet distillers co-products in ruminant diets are available (DeHaan et al, 1982; Farlin, 1981; Firkins et al., 1985; Fanning et al., 1999; Larson et al., 1993;Trenkle, 1997a;Trenkle, 1997b;Vander Pol et al., 2005a). In the experiments with finishing cattle, the replacement of corn grain with wet distillers co-product consistently improved feed efficiency. Figure 3 summarizes these studies conducted on wet distillers grains with energy value expressed relative to corn.
The energy value is consistently higher than corn.These experiments suggest a 15 to 25% improvement in feed efficiency when 30 to 40% of the corn grain is replaced with wet distillers co-product.The energy value at medium levels (12 to 28%, average of 17% of diet DM) is approximately 140 to 150% the energy of corn.When higher levels are used (average of 40%), the energy was 130% that of corn.The optimum level for feedlot producers to use is 30 to 40% of diet DM when plants are within 30 miles of the ethanol plant (Vander Pol et al., 2005a, 2005b). As the distance increases from the plant to the feedlot, the optimum inclusion of WDGS decreases to 20 to 30%.This comparison suggests that more WDGS can be fed; however, the optimum inclusion is dependent on more than just the energy value of WDGS.
COMPOSITION
Table 2 contains data on plant averages and some indication of variation for various corn milling co-products.Variation exists from plant to plant and within a plant.These table values should not replace sampling and analysis of feed from individual plants.The dry distillers grains plus solubles (DDGS),WDGS, and condensed corn distillers solubles (CCDS) are all from one plant in Nebraska and represent average values for 2003.The standard deviations are for composite weekly samples, not for load variation, which is not indicative of actual variation observed at a feedlot and may reduce variation by infrequent sampling. The plant with an excellent database on variability is the Cargill Blair facility.The standard deviation is low on DM change from load to load.This relates to two things: process development to minimize variation and culture of those operating the plants to minimize variation in feed products. The coefficient of variation (CV, %) can be calculated as: (standard deviation/average) x 100.
The energy values used in Table 3 are based on performance data summarized in this paper and other reviews. In another recent review of composition and variation in plants and across plants, the reader is referred to Holt and Pritchard (2004). Moisture and DM variation are probably of greatest importance with wet co-products. However, both fat and S can vary in wet distillers grains which could lead to changes in energy value and potential for toxicity, respectively.
USE IN FORAGE DIETS
Beef calves from weaning until they enter feedlots, developing heifers and beef cows are fed primarily forage diets. Especially in the winter, forages are low in protein and phosphorus and need to be supplemented. Corn gluten feed contains highly digestible fiber and degradable protein which are good sources of energy and protein for rumen microbes, especially in forage-based diets (DeHaan et al., 1983).Wet and dry corn gluten feed were compared to dry-rolled corn for growing calves fed grass hay, wheat straw, and corn stalklage.The gluten feed or corn replaced 40% of the forage (Oliveros et al., 1987).The supplements nearly doubled gains and improved feed conversion (Table 3).Wet and dry gluten feeds had better feed conversions than corn and WCGF had better feed conversion than DCGF. The apparent energy value of DCGF was 10% greater than corn, while WCGF was 31% higher than DCGF and 42% greater than corn in these forage-based diets.
Clearly, gluten feed is an excellent source of nutrients for forage-based diets.There is little to no starch in gluten feed, which results in no negative effect on fiber digestion. The DIP in gluten feed is an excellent source of protein for microbes. Protein in forages is highly degraded in the rumen. In certain production situations, cattle may need to be supplemented with undegraded (UIP; bypass) protein to meet metabolizable protein (MP) requirements. Distillers grains (wet or dry) are an excellent source of undegraded protein and phosphorus.  The values obtained from feeding trials for undegraded protein are shown in Table 4. Wet grains were compared to dry grains and the value of the protein was similar. This suggests that the high escape protein value of distillers grains is due to the innate characteristics of the protein and not to drying or moisture content, and does not appear to be influenced by acid-detergent insoluble protein (ADIN) which is a common measure of heat damaged protein.
Stocker calves, developing heifers and cows may need energy supplementation in addition to supplemental protein and phosphorus. It is advantageous if the same commodity can be used for supplemental energy as well as protein.We previously stated that distillers grains should have 120% the energy value of corn grain. Additional advantages for distillers grains are that it contains very little starch and therefore should not depress fiber digestion.
During drought conditions these co-products may be very competitive as energy supplements for use by ranchers. When forage quality is poor (winter) or quantity is limiting (drought), co-products may fit. Research has been initiated at the University of Nebraska-Lincoln to address the usefulness and value of dry co-products in cow-calf situations. Loy et al., (2004) concluded that DCGF decreases feed costs compared to conventional hay feeding when fed over the winter for developing heifers on a commercial, Nebraska ranch in the sandhills. In their study, a treatment system (TRT) was compared to their conventional management using over 550 heifers in each group across two years. The TRT system utilized only grazed winter forage and DCGF supplementation compared to some winter grazing, with hay and protein supplementation. Performance differences are presented in Table 5; however, little differences were observed in developing heifer performance by design. The major implication was reduced costs ($6.71 per heifer) through the winter while maintaining excellent performance and reproduction.
A similar experiment was conducted using DDGS (Stalker et al., 2006). Because of the higher energy content of DDGS, a smaller amount was needed to meet protein and energy requirements of these bred heifers (1353 heifers were used). Feeding DDGS and grazing winter range with heifers led to slightly better winter gains and changes in body condition compared to the hay-fed, control heifers. Pregnancy rates were 97% for both treatments. Most important, $10.47 per heifer was saved in feed costs by using DDGS and winter range versus a conventional system of hay, supplement, and range.
An experiment was conducted with 120 crossbred heifers to determine the value of dry distillers grains (DDGS) in high-forage diets, and to evaluate the effect of supplementing daily compared to three times weekly (Loy et al., 2003). Heifers were fed to consume grass hay ad libitum and supplemented with DDGS or dry rolled corn (DRC). Supplements were fed at two levels, and offered either daily or three times per week in equal proportions. Heifers supplemented daily ate more hay, gained faster (1.37 vs. 1.24 lb per day), but were not more efficient than those supplemented on alternate days (Table 6). At both levels of gain, DDGS heifers gained more and were more efficient than DRC fed heifers. The calculated net energy values for DDGS were 27% greater than for DRC.
The last area where co-products may fit in forage situations is with grazing corn residues. Incremental levels of WCGF were fed to calves grazing corn residues. Based on statistical and economical analysis of the data collected, feeding wet corn gluten feed (5.0-6.5 lb/ head/day; DM basis) will increase stocking rate on corn residue and reduce winter costs by 11%. Given that 3.5 lb DM/day wet corn gluten feed will meet the protein and phosphorus needs of calves, and feeding above 6.0 lb/d will not increase gains, wet corn gluten feed should be fed at 3.5-6.0 lb DM/day, producing gains from 1.28-1.88 lb/day (Jordon et al., 2001). In a similarly designed study using DDGS, Gustad et al. (2006) fed 1.5, 2.5, 3.5, 4.5, 5.5, and 6.5 lb/steer/d to calves grazing corn residue. Gains increased quadratically (P < 0.01) with ADG ranging from 0.90 to 1.81 lb.
CORN PROCESSING
Feeding corn milling co-products in feedlot diets reduces acidosis-related challenges from starch fed to ruminants. Both WCGF and WDGS have little to no starch remaining following the milling process.Therefore, feeding these co-products will dilute the starch that is fed and may influence rumen metabolism. Krehbiel et al., (1995) observed a decrease in subacute acidosis when WCGF was fed to metabolism steers. In many experiments, feeding WCGF results in increased DMI, which would be considered a symptom often observed with subacute acidosis.
Because processing corn increases rate of digestion by microbes, rumen acid production is increased and the risk of acidosis is increased (Stock and Britton, 1993). Feeding wet corn gluten feed (WCGF) helps prevent the risk of acidosis with high-grain diets (Krehbiel et al., 1995). Numerous studies have been conducted at the University of Nebraska-Lincoln to determine if energy values are markedly improved in diets containing WCGF when corn is more intensely processed. Scott et al. (2003) evaluated various corn processing techniques and observed improved feed conversions as processing intensity increased when feeding calves or yearlings (Table 7). Macken et al. (2006) fed DRC, FGC, SFC, and HMC processed as rolled (roller mill) and ground (tub grinder) to calves with all diets containing 25% WCGF. Whole corn was not fed in this study, but processing corn more intensely significantly improved performance.
Apparently, HMC appears to have greater energy value when diets contain WCGF than what was previously observed (diets not containing WCGF). Our conclusion is that intense processing has tremendous value in diets containing WCGF.
However, corn processing in diets containing WDGS appears to be somewhat different than diets containing WCGF.Vander Pol et al., (2006) fed diets containing either whole, DRC, HMC, a 50:50 blend of HMC and DRC (DM basis), SFC, or FGC to calf-feds for 168 days. Cattle fed DRC, HMC, or a combination of HMC and DRC gained more and were more efficient (lower feed conversion) than cattle fed whole corn. Interestingly, cattle fed steam-flaked corn and finely ground corn were not as efficient. It is unclear why more intense processing did not respond when diets contained WDGS similar to diets containing WCGF. More work is in progress to address the optimum corn processing method with diets containing WDGS.
COMBINATIONS OF CO-PRODUCTS
With the large expansion of ethanol plants in the Midwest, an option for many feedlots will be utilizing both WDGS and WCGF at the same time. In addition to their commercial availability, another reason for feeding a combination of WDGS and WCGF is due to their nutritional profiles. Synergistic effects in feeding a combination of these co-products may be observed because of differences in fat, effective fiber, and protein components. Loza et al., (2004) fed yearling steers a 50:50 blend of WDGS and WCGF (DM basis) at inclusion levels ranging from 0 to 75% DM.This experiment also evaluated different forage levels.A level of 7.5% alfalfa hay was used across all the treatments, and a lower alfalfa level was included in each of the co-product diets, decreasing the forage inclusion as the rate of inclusion of co-products in the diets increased (i.e. 25% blend had 5% alfalfa in the lower forage treatment, 75% blend had 0% alfalfa in the lower forage treatment). Results indicated that there were no differences in cattle performance between forage levels for each co-product blend level. The lack of differences in performance with decreasing forage would indicate that the co-product inclusion was enough to prevent the negative consequences of sub-acute acidosis (Table 8). The analysis of the pooled data from each co-product level indicated that the performance of the steers fed the maximum co-product level (75%), regardless of the forage level, was not different than a typical corn based diet (0% co-product blend). However, the diets including a 25 and 50% blend of WDGS and WCGF resulted in significantly better animal performances than the control. In conclusion, it is feasible to decrease the forage levels with high inclusion of co-products. Producers may also feed levels as high as 75% without negatively affecting performance. However, optimum inclusion rates of a co-product blend would be between 25 and 50% DM.
Feeding a combination of WDGS and WCGF also offers producers greater flexibility.A major challenge facing some ethanol plants is not having feed for cattle feeders on a consistent basis. Cattle do not respond well if either WDGS or WCGF, as sole co-products in the diet, are removed and replaced with corn abruptly.Therefore, one approach would be to feed a combination to ensure that at least one co-product is consistently in the ration.
NEW ETHANOL INDUSTRY CO-PRODUCTS
The evolving ethanol industry is continually striving to maximize ethanol production efficiency. Changes associated with this progress will provide innovative new co-product feeds for producers to utilize that may be quite different nutritionally when fed to cattle. One example of a new co-product feed is Dakota Bran Cake. Bran cake is a distillers co-product feed produced as primarily corn bran plus distillers solubles produced from a hybrid wet and dry milling process. On a DM basis, bran cake contains less protein than WDGS and WCGF, similar NDF to both feeds and similar to slightly less fat content as WDGS.A study by Bremer et al., (2005) evaluated Dakota Bran Cake inclusion up to 45% DM by comparing 0, 15, 30, and 45% of diet DM. Results indicated improved final weight, ADG, DMI and F:G compared to feeding a blend of highmoisture and dry-rolled corn, suggesting this specific feed has 100 108% of the energy value of corn. Dakota Bran Cake is only one example of how new ethanol industry co-products will feed relative to traditional finishing rations. Each new co-product feed needs to be analyzed individually for correct feeding value. Changes to plant production goals and production efficiency have a significant impact on the feeding value of co-products produced.
CONCLUSIONS
Distillers grains have 120 to 150% the energy value of dry rolled corn in beef finishing diets and wet corn gluten feed has 100 to 110% the energy value depending on steep level in gluten feed. Dry co-products have less energy.These co-products also work very well in forage feeding situations as both protein supplements but also as an energy supplement or forage replacement (particularly high quality forages).
With feedlot cattle, more intense corn processing may be optimal for diets containing WCGF. It appears that with diets containing WDGS, high-moisture corn and dry-rolled corn work well. In the future, with increased supply of co-products, feeding combinations of WDGS and WCGF may be advantageous. It also appears that many new coproducts will be available in the future as the processes of making ethanol and other products from corn evolve. These new feeds should be evaluated with performance data to determine how the new co-products will feed.
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