Ethanol byproducts or coproducts result from the fermentation of grain to produce ethanol – either for fuel or for human consumption.
The following review discusses feeding ethanol byproducts to dairy and beef cattle.
It looks at the nutrients of ethanol byproducts and the response of lactating cows.
Byproducts from the fermentation other grains or feed sources will be mentioned, although research is limited.
Ethanol byproducts or coproducts (I may use the two terms interchangeably) result from the fermentation of grain to produce ethanol – either for fuel or for human consumption.
Currently in the U.S.A., most ethanol is produced by dry grinding, with dried distillers grains plus solubles (DDGS) as the main byproduct (Rausch and Belyea, 2006). Quantitatively, dry grind processing of 100 kg of corn produces approximately 40.2 L of ethanol, 32.3 kg of DDGS, and 32.3 kg of carbon dioxide.
Wet milling is usually used for producing corn oil or corn sweeteners such as dextrose and high fructose corn syrup, but the starch can be fermented to produce ethanol. Byproducts of this process include corn gluten feed (CGF) and corn gluten meal (CGM). The CGF consists mainly of corn bran and steep liquor. Corn gluten meal is a high protein byproduct of wet milling while corn germ meal remains after extraction of oil from the corn germ. Quantitatively, wet milling 100 kg of corn produces 67.2 kg corn starch (which can be fermented to ethanol), 19.6 kg CGF, 5.7 kg CGM, and 7.5 kg corn germ (50% oil) (Long, 1985). Both distillers grains and CGF can be fed wet or dried with similar results.
The following review discusses feeding ethanol byproducts, especially DDGS and CGF to dairy and beef cattle. Other byproducts such as condensed corn distillers solubles (CCDS), corn germ, and some possible new products will be mentioned. Byproducts from the fermentation other grains or feed sources will be mentioned, although research is limited.
Nutrient Content of Ethanol Byproducts
Nutrient content of the major ethanol coproducts is listed in Table 1. Values have recently been modified for “new generation” DGS (Spiehs et al., 2002) and for energy values (Birkelo et al., 2004). New generation products tend to contain more protein, energy, and available phosphorus than distillers grains from older ethanol plants, likely reflecting increased fermentation efficiency.
Ethanol coproducts contain relatively high amounts of phosphorus. A benefit if additional phosphorus is needed in diets, but a negative if manure applications are limited by phosphorus.
Virtually all distillers grains is marketed as distillers grains plus solubles, although this may change as processors fractionate distillers products into various components. The composition of corn distillers grains is essentially the same with or without solubles added, except for a lower phosphorus content (~0.4%) without solubles because the solubles are quite high in phosphorus (~1.35%).
The protein content of DDGS is often slightly higher and the fat content slightly lower without solubles. If a DGS product contains substantially more fat (e.g. >15%) and/or phosphorus (e.g. >1.0%) than the values listed in Table 1, it is very likely that more than normal amounts of distillers solubles were blended with the distillers grains, or that the processor had problems with separation of materials during the handling of solubles. Such variations emphasize the importance of obtaining analytical data for the specific product being fed, as well as the importance of suppliers providing uniform, standardized products. Inconsistent, variable products are problems for some suppliers, stimulating other suppliers to offer consistent, premium quality DDGS.
Both distillers grains and CGF are available in wet or dried with similar nutrient contents. The distillers grains available in recent years contain more energy than previously published values. Research by Birkelo et al. (2004) indicated that wet corn DGS contained approximately 2.25 Mcal/kg of NEL,; 10 to 15% more energy than published in older references and even more than in the recent dairy NRC (2001) for DDGS. This likely reflects a higher energy value for newer generation distillers grains and does not necessarily reflect higher energy in wet than in dried DGS.
Both distillers grains and CGF contain large amounts of NDF but low amounts of lignin. Thus, these are readily digestible fiber sources, which may partially replace forages as well as concentrates in dairy and beef diets. These nonforage fiber sources can supply energy needed for lactation or growth without the ruminal acid load caused by rapidly fermented starch sources (Ham et al., 1994). Distillers coproducts can partially replace forages when supplies are limited; however, because of the small particle size, DGS and wet CGF may lack sufficient “effective fiber” to prevent milk fat depression (Cyriac et al., 2005; Allan and Grant, 2000). Wet CGF was only 11 to 13% as effective as alfalfa hay in maintaining ruminal pH and rumination activity but 74% as effective as alfalfa silage in maintaining milk fat percentages (Allan and Grant, 2000).
Less information is available on the nutrient content of DDGS produced from the fermentation of other grains such as wheat, sorghum, or barley. However, the composition usually reflects the nutrient content of the grain, i.e. higher protein for wheat and barley DDGS than for corn DDGS and higher or lower protein for sorghum DDGS, depending on the source used.
Since inclusion of the solubles has minimal effect on nutrient composition, most of the performance studies reported below use data for distillers grains with or without solubles interchangeably. Distillers grains, often referred to corn distillers grains, is a good source of ruminally undegradable protein (RUP). The reported value of 55% of CP as RUP is probably correct for most cases, although reported values vary somewhat. Most reported values range from 47% to 69% RUP. Wet DGS usually have lower RUP values, often 5 to 8% lower concentrations of RUP than dried DGS (Firkins et al., 1984; Kleinschmit et al., 2007). Most of the readily degradable corn proteins are degraded during the fermentation process, thus corn DDGS protein will be proportionately higher in RUP than corn grain. However, if RUP values for DDGS are quite high (e.g. >80% of CP), it may be advisable to check for heat damaged, undigestible protein. Traditionally, a golden yellow color was used as a quality indicator for DDGS. However, research results do not support the theory that color is an accurate indicator of protein quality (Belyea et al., 2004; Powers et al., 1995; Kleinschmit et al., 2006b).
Response of Lactating Cows and Growing Cattle
A meta analysis conducted by Kalscheur (2005) utilized virtually all modern research data available (98 treatment comparisons) evaluating DGS in lactating cow diets. Amounts of DGS fed ranged from 4.2% of total diet DM (Broderick et al., 1990) to 41.6% of DM (Van Horn et al., 1985). Production was the same as or higher for DGS diets compared with control diets in virtually all experiments except when very large amounts of wet DGS were fed (i.e. 30% or more of diet DM). Production on DGS diets was similar or higher than production achieved with soybean meal, even when diets were formulated for equal RUP (Pamp et al. 2006). Florida research (Powers et al., 1995) indicated higher production with DDGS from whiskey or fuel ethanol plants than when fed soybean meal. However, with a potentially heat damaged DDGS product, milk production was lower than when fed a higher quality DDGS product; however, production was still similar to soybean meal. An evaluation of specially processed DDGS products intended to have excellent feed value resulted in higher milk production for both the high quality control and the specialty DDGS products than for the soybean meal-based control diet. Only small differences due to the improved DDGS quality were noted.
We are completing the second year of a trial in which cows were fed wet DGS at 15% of diet DM for two complete lactations, including the dry period. After the first year, there were no differences in production (31.7 and 33.6 kg/d for control and wet DGS), while fat percent (3.75 and 4.07), protein percent (3.29 and 3.41), and feed efficiency (1.30 and 1.57 kg FCM/kg DMI) were greater for cows fed wet DGS (Mpapho et al., 2006). Reproductive efficiency and cow health were similar for both dietary groups.
The protein quality of corn DDGS is fairly good. As with most corn products, lysine is the first limiting amino acid in corn DGS for lactating cows, but corn DGS is a very good source of methionine. Therefore, sometimes (Nichols et al., 1998) milk production increases when DDGS is supplemented with ruminally protected lysine and methionine or when it is blended with higher lysine protein sources. Kleinschmit et al. (2006b) showed that, while there may be differences in the protein quality of various sources of DDGS (Kleinschmit et al., 2007), differences in yields of milk and milk protein might be slight, unless a product is greatly heat-damaged. Slightly greater production was observed when 15% DDGS was fed with high alfalfa rather than high corn silage diets, likely reflecting an improved amino acid status with the "blend" of alfalfa-DDGS proteins versus a diet containing predominantly corn-based proteins (Kleinschmit et al. 2006a).
Wet versus Dried DGS.
Data from both wet and dried distillers grains has been presented almost interchangeably, because nutrient contents (DM basis) are essentially the same for both wet and dried DGS, except for possibly slightly lower RUP values with wet than with dried DGS. Few comparisons between wet and dried DGS have been published.
A comparison between wet or dried corn or sorghum DGS for lactating cows showed similar production for both wet and dried DGS but about 6% more milk (P < 0.13) with corn versus sorghum DGS (Al-Suwaiegh et al., 2002). A non-significant tendency (P = 0.13) for greater production was observed for lactating cows fed wet DGS instead of dried DGS (Anderson et al. (2006). For growing and finishing beef cattle, animal performance was similar with either wet or dried DGS (Ham et al., 1994).
The main considerations regarding the use of wet versus dried DGS are handling and cost. Dried products can be stored for extended periods of time, can be shipped more economically and conveniently, and can be easily blended with other dietary ingredients. Some reports suggest DDGS may “set up” when shipped extended distances in rail cars, but this seems to be related to moisture and temperature problems at some ethanol plants.
Feeding wet DGS avoids the need to dry the product, but there are other factors to consider when feeding wet DGS that are not concerns when feeding dried DGS. Wet DGS will not remain fresh and palatable for extended periods of time; 5 to 7 days is the norm. Acceptable storage times will vary somewhat with environmental temperature; products will spoil and become unpalatable more rapidly in hot weather, but may stay fresh as long as three weeks in cool conditions. Surface molds usually produce some feed loss; a problem that wouldn’t be a consideration with DDGS. The addition of preservatives such as propionic acid or other organic acids may extend the shelf life of wet DGS (Spangler et al., 2005) but few refereed publications document such. Wet DGS have been successfully stored at SDSU (South Dakota State University) in silo bags for more than six months (Kalscheur et al., 2002; 2003; 2004a,b). The wet DGS was stored alone or blended with soyhulls (Kalscheur et al., 2002), with corn silage (Kalscheur et al., 2003), and with beet pulp (Kalscheur et al., 2004). Some field reports indicate successful preservation of wet DGS for more than a year in silo bags.
Milk composition is usually not affected by feeding DDGS provided recommended ration formulation guidelines are followed. Some field reports indicated milk fat depression with diets containing more than 10% of ration DM as wet DGS (Hutjens, 2004); however, those observations are not supported by research results. A meta analysis conducted by Kalscheur (2005) showed no decreases in milk fat content when diets contained wet or dried DGS at any level, even as high as 40% of DM intake. In fact, milk fat content was usually numerically highest for diets containing DGS. Incidentally, most of these studies were conducted during early to mid lactation.
Milk fat content can be lower with DGS when diets contain less than 50% forage (Kalscheur, 2005). This result suggests the reason for field observations of milk fat depression with DGS. Because DGS contains high levels of NDF, it is often used as a forage replacement when forage is expensive or in short supply. However, the small particle size of DGS means that it is not an “effective fiber” source and cannot replace forages on a one for one basis.
Milk fat concentration decreased linearly while milk production remained unchanged and milk protein content increased when corn silage (0, 7, 14, or 21% of DM) was replaced with DDGS, even though dietary NDF content remained unchanged (Cyriac et al., 2005). The control diet contained 40% corn silage, 15% alfalfa hay, and 45% concentrate mix. Thus, the key to maintaining milk fat tests is to feed sufficient amounts of forage fiber.
Because the fat in DGS, especially corn DGS, is largely unsaturated and typically contains more than 60% linoleic acid, a modest increase in unsaturated fatty acids concentration is expected in the milk of cows fed DGS (Schingoethe et al., 1999). Leonardi et al. (2005) and Anderson et al. (2006) also reported modest increases in the healthful fatty acid cis-9,trans-11 conjugated linoleic acid (CLA) and its precursor vaccenic acid (trans-11C18:1).
Milk protein content is seldom affected by feeding DGS unless protein is limiting in the diet. Then the lysine limitation in DGS may cause a slight decrease in milk protein content (Kleinschmit et al., 2006b). This effect may be more noticeable in diets that contain more than 30% DGS (Kalscheur, 2005). Milk protein content is typically decreased about 0.1% with fat added from any source, so that can be a minor consideration when feeding DGS; however, most studies with DGS showed no effect on milk protein content.
How much corn DGS can be fed? A number of experiments suggest that up to 20% of ration DM can be fed as distiller’s grains. With typical feed intakes of lactating cows, this would be approximately 4.5 to 5.5 kg of dried DGS or 15 to 17 kg of wet DGS per cow daily. Palatability problems generally do not exist at this level of feeding and nutritionally sound diets can typically be formulated.
With diets containing higher proportions of corn silage, even greater amounts of DDGS may be used; however, protein quality (e.g. lysine limitation) and phosphorus concentration may become factors to consider.
With diets containing higher proportions of alfalfa, less DGS may be needed to supply the protein required in the diet. In fact, diets with 20% DGS may supply excess protein. When feeding more than 20% distillers grains, one is likely to feed excess protein, unless forages are all or mostly corn silage and/or grass hay.
Grings et al. (1992) observed similar DM intake and milk production when cows were fed as much as 31.6% of ration DM as DDGS. Schingoethe et al. (1999) fed slightly more than 30% of the ration DM as wet DGS with decreased DM intake but no decrease in milk production, likely reflecting the higher NEL content of the wet DGS diet.
However, possible problems were noted when corn DGS provided more than 20 to 25% of the ration DM (Hippen et al., 2003; 2004). Dry matter intake decreased with a corresponding decrease in milk production when wet DGS supplied more than 20% of the diet DM (Hippen et al., 2003). Gut fill may have limited DM intake of these wet diets (40 to 46% DM) because total DM intake often decreases when the diet is less than 50% DM, especially when fermented feeds are fed (NRC, 2001). However, when dried DGS was fed (Hippen et al., 2004), DM intake and milk production still decreased when diets contained 27 to 40% DDGS. The meta analysis of 24 experiments (Kalscheur, 2005) noted highest DM intakes and milk production with diets containing 20 to 30% DGS with DM intakes and production decreasing with 30 to 40% wet DGS.
Distillers grains for beef cattle.
Beef cattle have been successfully fed as much as 40% of ration DM as wet or dried DGS (Al-Suwaiegh et al., 2002; Ham et al., 1994; Larson et al., 1993). A Minnesota study (Roeber et al., 2005) fed up to 50% of DM as wet or dried DGS with no effect on beef tenderness or palatability. Diets cited above used DGS primarily as energy sources but, admittedly, contained more protein and phosphorus than finishing cattle needed. These experiments suggested that wet DGS contained 29 to 40% more NEgain than dry-rolled corn, but dried DGS contained only 21% more NEgain than dry-rolled corn (Ham et al., 1994). Increased feed efficiency with distillers grains products or wet CGF (Krehbiel et al., 1995) fed in place of corn may in part be due to fewer off-feed problems and reduced subacute acidosis (Ham et al., 1994; Larson et al., 1993). Even though DGS contain as much or more energy than corn, energy in DGS is primarily in the form of digestible fiber and fat while corn energy is mainly in the form of starch. Ruminal starch fermentation is more likely to result in acidosis, laminitis, and fatty liver. Corn wet DGS was more digestible than sorghum wet DGS, and wet DGS products were more digestible than dried DGS (Lodge et al., 1997).
Distillers Grains Blended with Other Feeds.
Distillers grains have been successfully fed blended with other feeds for both beef and dairy cattle. Lodge et al. (1997) reported that a composite of wet CGF, condensed distillers solubles, corn gluten meal, and tallow, formulated to be similar in nutrient content to wet DGS improved the feed efficiency of finishing steers compared to wet CGF or corn.
Several experiments have been conducted at SDSU in which wet DGS was blended with other high fiber feeds. Such approaches may be helpful in times when forage supplies are limited or expensive. For instance, a 70:30 (DM basis) blend of wet DGS and soyhulls reduced the dustiness of soyhulls, reduced the seepage that is common with wet DGS, provided more desirable protein (21% CP) and P (0.6%) contents, and yet provided a high energy, high fiber feed (Kalscheur et al., 2002). Growth rates of heifers fed the blend were similar (1.22 and 1.27 kg/d) to gains on conventional diets (Kalscheur et al., 2004). A blend of wet DGS (69% of DM) and corn stalks (31%) produced weight gains that were lower (1.04 kg/d) than those on conventional diets (1.27 kg/d). Ensiling wet DGS alone or in combination with corn silage indicated that preservation of each could be enhanced by combining the feedstuffs, with a 50:50 blend likely optimal (Kalscheur et al., 2003).
Corn Distillers Solubles
Distillers solubles are usually blended with the distillers grains before drying to produce DGS, but they may be fed separately. DaCruz et al.(2005) fed 28% DM condensed corn distillers solubles (CCDS) at 0, 5, and 10% of total ration DM to lactating cows. Milk production (34.1, 35.5 and 35.8 kg/d for 0, 5, and 10% CCDS diets) increased with the CCDS, although milk fat content (3.54, 3.33, and 3.43%) was slightly lower and milk protein content (2.93, 2.97, 2.95%) was unaffected by diets. As much as 20% of total ration DM consisted of CCDS (4% fat from the CCDS) with no apparent adverse affects on DM intake or milk composition (Sasikala-Appukuttan et al., 2006). Milk yield tended to be higher for cows fed 10 and 20% CCDS than for cows fed the control diet. Thus, CCDS by itself can be a good feed for dairy cattle. However, feeding much as 20% CCDS is not recommended because those diets contained more than 0.5% phosphorus. Pingal and Trenkle (2005) fed 12% of DM as CCDS to finishing steers with good animal performance results. Condensed and thin distillers solubles have also been successfully used as protein and energy sources in beef cattle diets (see Ham et al., 1994).
Other Distillers Products
A growing list of distillers products will likely become available as livestock feed in the future as processors continue to improve the efficiency of ethanol production and look for ways to fractionate byproducts resulting from the process. For instance, distillers bran is a new byproduct feed produced as primarily corn bran plus distillers solubles (53% DM) containing 14.9% CP. When fed to finishing steers, animal performance was similar to DDGS at the same inclusion level (Bremer et al., 2005).
The germ removed from corn grain prior to ethanol production (~21% fat) was fed to lactating cows at 0, 7, 14, and 21% of ration DM (Abdelqader et al., 2006). Inclusion at 7 and 14% of DM increased milk and fat yields, however, feeding 21% corn germ decreased the concentration and yield of milk fat. Corn germ from wet milling operations may contain 45% or more fat, but feeding trials with that product are limited.
Corn Gluten Feed
Corn gluten feed, often fed as wet CGF, is a relatively high fiber, medium-energy, medium-crude protein product. The energy value of wet CGF is 92 to 100% of the energy value of shelled corn (Firkins et al., 1985; Ham et al., 1995); values were slightly lower for dry CGF. Schrage et al. (1991) determined the NEmaint. and NEgain of wet CGF to be 1.60 and 1.32 Mcal/kg of DM, respectively. Lactating cows can consume quite large amounts of CGF with acceptable performance, but the response was more variable in earlier studies (see Van Baale et al., 2001). Staples et al. (1984) reported linear declines in DM intake and milk yield as amounts of wet CGF increased from at 0 to 40% of DM in 50% corn silage diets.
Dry matter content of the total diet may have been part of the problem as mentioned earlier regarding the feeding of wet DGS. However, Armentano and Dentine (1988) observed no reductions in DM intake and milk yield when diets contained as much as 7.9 kg/d (~36% of ration DM) as wet CGF. Wet CGF replaced only concentrates in most of the above studies. When wet CGF replaced up to 35% of ration DM as a mix of alfalfa hay, corn silage, and corn grain, milk production was greater than when fed the control diet (Van Baale et al., 2001). In experiments that included as much as 45% of ration DM as wet CGF, Schroeder (2003) concluded that 18.6% of dietary DM as wet CGF in place of portions of both forage and concentrate would maximize milk yield without negatively affecting milk composition or feed efficiency.
Cattle can be fed very large amounts of wet CGF with acceptable animal performance. Sindt et al. (2003) obtained the highest weight gains and feed efficiencies when diets fed to finishing steers contained 30% wet CGF rather than 0 or 60% wet CGF. This amount (30% of DM) was similar to the 27% of DM as wet CGF that Bernard et al. (1991) indicated could be fed to lactating cows without altering milk yields. A summary of beef feedlot research (Stock et al., 1999) indicated that the efficiency of gain was improved by 5% when diets containing 25 to 50% wet CGF were compared to dry-rolled corn.
Data from Boddugari et al. (2001) indicated that a new wet corn milling product
(CMP) can effectively replace all of the concentrate and up to 45% of the forage in the diet of lactating cows. The CMP, which is similar to wet CGF, was composed of corn bran, fermented corn extractives, corn germ meal, and additional sources of ruminally undegradable protein to increase the metabolizable protein content of the product. This wet CMP contained (DM basis): 23.1% CP, 9.9% RUP, 40.3% NDF,13.7% ADF, and 2.6% ether extract. A modified corn fiber (MCF) produced by a secondary bacterial and yeast-driven fermentation of the corn bran may enable corn processors to more fully recover ethanol from corn (Peter et al., 2000). However, feeding MCF (23.9% CP, 49.4% NDF, 45.4% ADF) resulted in poorer performance of heifers, suggesting a limited feeding value because of the high acid detergent insoluble nitrogen content and slow protein digestion.
Corn Gluten Meal
Corn gluten meal (CGM) is a high protein (65% CP) high RUP (75% of CP) feed that is a very good protein supplement. However, it is best to blend CGM with other protein supplements for optimal animal performance. Because of its high RUP level and lysine limitation, feeding CGM as the only protein supplement did not support the same amount of milk production as soybean meal-containing diets in a series of multi-university studies, even when the CGM diets were supplemented with ruminally protected lysine and methionine (Polan et al., 1991). A blend of several high quality proteins (blood meal, CGM, canola meal, and fish meal) supported milk production similar to production supported by soybean meal-containing diets (Piepenbrink et al., 1998).
One doesn’t know what corn coproducts will be available to the feed industry in the future. However, improved products and new products are likely to become available. For instance, improvements in fermentation technology already provide DDGS today that contains more protein and energy than DGS of previous years contained. It is also becoming feasible to "fractionate" DGS into products that are higher in protein, other products that are higher in fat or in fiber, and products that are higher or lower in phosphorus (Rausch and Belyea, 2006).
And some products from ethanol production may find their way into human food uses and non-food uses such as building products. Also, some ethanol producers are currently evaluating the use of much of the fat in DGS as biodiesel. This fat may be extracted from the germ prior to ethanol fermentation or from the distillers solubles.
Table 1. Nutrient content of ethanol byproducts (1)
||% of DM
|RUP(5) % of CP
|Neutral detergent fiber (NDF)
|Acid detergent fiber (ADF)
(1) Most data are from NRC (1996, 2001), Spiehs et al. (2002), and Birkelo et al. (2004)
(2) DDGS = corn distillers grains
(3) CGF = corn gluten feed
(4) CGM = corn gluten meal
(5) RUP = ruminally undegradable protein
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