[Today’s] distillers grains (DGS) tend to contain more protein, energy and available phosphorus than DGS from older ethanol plants, which likely reflects increased fermentation efficiency. Ethanol coproducts contain relatively high amounts of phosphorus, which can be a plus if additional phosphorus is needed in diets or a minus if excess phosphorus in manure needs to be disposed.
Virtually all DGS is marketed as DGS plus solubles, although this may change in the future as some processors fractionate distillers products into various components. The composition of corn DGS is essentially the same with or without solubles added, except for a lower phosphorus content without solubles because the solubles are quite high in phosphorus. Therefore, most animal performance studies use data for DGS with or without solubles interchangeably.
Corn distillers grains is a good source of ruminally undegradable protein (RUP). The reported value of 55 percent of crude protein (CP) as RUP is probably an appropriate figure to use in most cases, although some variation in reported values exist. Most reported values range from 47 to 69 percent RUP, with the higher quality products usually containing less than 64 percent RUP.
Wet DGS usually has 5 to 8 percent lower concentrations of RUP than does dried DGS. Most of the readily degradable proteins in corn have been degraded during the fermentation process, thus the protein remaining in the corn DGS is going to be proportionately higher in RUP than in the original corn. However, if RUP values for DGS are quite high (e.g. greater than 80 percent of CP), it may be advisable to check for heat- damaged, indigestible protein. While some may wish to think that a golden yellow color is a good indication of quality for DGS, research data from Belyea et al. indicated that color is sometimes but often not an accurate indicator of protein quality.
Distillers grains available in recent years contain more energy than older “book” values. Research by Birkelo et al. indicated that wet corn DGS contained approximately 10 to 15 percent more energy than published in even the recent dairy National Research Council (NRC) for dried DGS. This likely reflects a higher energy value for newer generation DGS and does not necessarily reflect higher energy in wet than in dried DGS; that is a separate comparison that has not been made.
Both DGS and corn gluten feed (CGF) contain large amounts of neutral detergent fibers (NDF) but low amounts of lignin. These readily digestible fiber sources can serve as partial replacements for forages as well as for concentrates in diets of dairy cattle. These nonforage fiber sources can supply energy needed for lactation or growth without the ruminal acid load caused by rapidly fermented starchy compounds. Such nonforage fiber sources of NDF can partially replace forages at times when forage supplies may be limited; however, because of the small particle size, DGS and wet CGF may lack sufficient “effective fiber” to prevent milk fat depression.
Response of lactating cows to DGS
Milk production and composition data were summarized from more than two dozen research trials with 98 treatment comparisons reported between 1982 and early 2005 in which corn distillers grains, either wet or dried, were fed to lactating cows. Amounts of DGS fed ranged from 4.2 percent of total diet DM to 41.6 percent of DM.
Production was the same as or higher when fed DGS than when fed control diets in virtually all experiments except possibly when fed very large amounts (i.e. 30 percent or more of diet DM) as wet DGS. In experiments that compared DGS to soybean meal as the protein supplement, production was similar or higher, even when DGS and soybean-based diets were formulated to be equal in RUP.
Florida research indicated higher production when fed DGS from whiskey or from fuel ethanol plants than when fed soybean meal. However, when they fed a DGS product that was darker and possibly heat-damaged, milk production was lower than when fed lighter, golden colored DGS but still similar to production when fed soybean meal. But be cautioned because research data from Belyea et al. indicated that color is often not an accurate indicator of protein quality.
When Kleinschmit et al. used a standard, good quality DGS to evaluate the response to two specially processed DGS products intended to have even better quality, milk production was higher for all three DGS products than for the soybean meal-based control diet, with only small differences in response due to the improved DGS quality.
We are completing the second year of a trial in which cows were fed 15 percent of diet DM as wet DGS for the entire lactation, during the dry period and into the second lactation. After the first year, there were no differences in production, while fat percent, protein percent and feed efficiency were greater for cows fed wet DGS. Reproductive efficiency and cow health were similar for both dietary groups.
The quality of protein in corn DGS 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, but not always, milk production increased when fed supplemental ruminally protected lysine and methionine with DGS, or when the DGS was blended with other protein supplements that contained more lysine.
While there may be differences in protein quality of various sources of DGS present today, differences in yields of milk and milk protein might be slight, unless a product is greatly heat-damaged. Kleinschmit et al. observed slightly greater production when 15 percent DGS was fed in high alfalfa versus high corn silage diets, likely reflecting an improved amino acid status with the “blend” of alfalfa-DGS proteins versus a diet containing predominantly corn-based proteins.
Wet versus dried DGS
The response to wet or dried DGS is usually considered to be equal; however, very few trials actually compared wet versus dried DGS; most trials simply compared DGS to a control diet. When Al-Suwaiegh et al. compared wet versus dried corn or sorghum DGS for lactating cows, they observed similar production for both wet and dried DGS but 6 percent more milk with corn versus sorghum DGS. Anderson et al. observed greater production when fed either wet or dried DGS than when fed the control diet, a tendency for greater production when fed wet DGS instead of dried DGS and a tendency for greater production when fed 20 percent of the ration DM as DGS versus 10 percent, either wet or dried.
The main considerations regarding the use of wet versus dried DGS are handling and costs. Dried products can be stored for extended periods of time, can be shipped greater distances more economically and conveniently than wet DGS and can be easily blended with other dietary ingredients. Some possible problems with DGS setting up when shipped extended distances in rail cars seems to be related to moisture and temperature conditions that some ethanol plants are addressing.
Feeding wet DGS avoids the costs of drying the product, but there are other factors to consider with wet DGS that are not concerns when feeding dried DGS. Wet DGS will not remain fresh and palatable for extended periods of time; five to seven days is the norm. Surface molds occasionally occur, thus there is usually some feed lost. The addition of preservatives may extend the shelf life of wet DGS by a few days but refereed journal publications that document such results are limited.
We at South Dakota State University (SDSU) successfully stored wet DGS for more than six months in silo bags. The wet DGS was stored alone or blended with soy hulls, with corn silage and with beet pulp. Some field reports indicate successful preservation of wet DGS for more than a year in silo bags.
Milk composition when fed DGS
The composition of milk is usually not affected by feeding DGS unless routinely recommended ration formulation guidelines, such as feeding sufficient amounts of forage fiber, are not followed. Some field reports indicated milk fat depression when diets contained more than 10 percent of ration DM as wet DGS; however, those observations are not supported by research results.
The analysis showed no decreases in milk fat content when diets contained wet or dried DGS at any level, even as high as 40 percent of DM intake. In fact, the milk fat content was usually numerically highest for diets containing DGS.
The only time when milk fat content may have been lower with DGS was when diets contained less than 50 percent forage. That result hints at why field observations of milk fat depression may have occurred. Because DGS contains an abundance of NDF, one may be tempted to decrease the amounts of forage fed when formulations indicate more than sufficient amounts of NDF. However, the small particle size of DGS means that its “effective fiber” is not as great as that of the forage fiber it replaced.
The fatty acid content of milk fat when cows are fed DGS is not expected to be affected greatly but has been evaluated in a few studies. Because the fat in DGS, especially corn DGS, is quite unsaturated with typically more than 60 percent linoleic acid, it is logical to expect a modest increase in concentrations of unsaturated fatty acids in the milk produced.
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. This effect may be more noticeable in diets that contain more than 30 percent DGS, reflecting the high ruminally undegraded protein (RUP) and lysine limitation in DGS.
How much DGS can be fed?
We at SDSU and other researchers have demonstrated in several experiments that dairy producers can easily feed up to 20 percent of ration DM as distillers grains. With typical feed intakes of lactating cows, this is approximately 4.5 to 5.5 kilograms (kg) of dried DGS or 15 to 17 kg of wet DGS per cow daily. There are no palatability problems and one can usually formulate nutritionally balanced diets with up to that level of distillers grains in the diet using most combinations of forages and concentrates.
For instance, with diets containing 25 percent of the dry matter as corn silage, 25 percent as alfalfa hay and 50 percent concentrate mix, the DGS can replace most – if not all – of the protein supplement such as soybean meal and a significant amount of the corn that would normally be in the grain mix. This was illustrated in the experiment by Anderson et al. in which feeding 20 percent of the diet DM as wet or dried DGS replaced 25 percent of the corn and 87 percent of the soybean meal fed in the control diet.
With diets that contain higher proportions of corn silage, even greater amounts of DGS may be usable; however, the need for some other protein supplement, protein quality (e.g. lysine limitation), and phosphorus concentration may become factors to consider. With diets containing higher proportions of alfalfa, less than 20 percent DGS may be needed to supply the protein required in the diet. Thus, there are no strong advantages to feeding more than 20 percent DGS, but the possibility of feeding excess protein or phosphorus may occur.
Grings et al. observed similar DM intake and milk production when cows were fed 31.6 percent of ration DM as DGS. Schingoethe et al. fed slightly more than 30 percent of the ration DM as wet DGS with decreased DM intake but no decrease in milk production. However, research by our group in which as much as 40 percent of ration DM was fed as DGS indicated possible problems when corn DGS provided more than 20 to 25 percent of the ration DM. Dry matter intake decreased with a corresponding decrease in milk production when wet DGS supplied more than 20 percent of the diet DM.
Gut fill may have limited DM intake of these wet diets (40 to 46 percent DM) because total DM intake often decreases when the diet is less than 50 percent DM, especially when fermented feeds are fed. However, when dried DGS was fed, DM intake and milk production still decreased when diets contained 27 to 40 percent DGS. An interesting observation is that the highest DM intakes and milk production occurred when diets contained 20 to 30 percent DGS although, as expected, DM intakes and production decreased with 30 to 40 percent wet DGS.
Distillers grains blended with other feeds
Several experiments were conducted at SDSU in which wet DGS was blended with other high fiber feeds. Such approaches may be helpful during times when forage supplies are limited or expensive. For instance, a 70-to-30 (DM basis) blend of wet DGS and soy hulls reduced the dustiness of soy hulls, reduced the seepage that is common with wet DGS, provided more desirable protein (21 percent CP) and P (0.6 percent) contents, and yet provided a high energy, high fiber feed. We don’t have lactation data on these forage blends but growth rates of heifers fed the blend were similar to gains when fed conventional diets.
Heifers fed a blend of wet DGS (69 percent of DM) and corn stalks (31 percent), had lower weight gains than when fed conventional diets. 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-to-50 blend likely optimal.
Corn distillers solubles
Distillers solubles are usually blended with the distillers grains before drying to produce DGS, but the solubles may be fed separately. Some include solubles in diets to decrease dustiness and decrease ingredient separation. DaCruz et al. fed 28 percent DM condensed corn distillers solubles (CCDS) at 0, 5 and 10 percent of total ration DM to lactating cows. Milk production increased when fed the CCDS, although milk fat was slightly lower and milk protein was unaffected by diets.
Recently, Sasikala-Appukuttan et al. fed as much as 20 percent of the total ration DM as CCDS with no apparent adverse affects on DM intake or milk composition. Milk yield tended to be higher for cows fed 10 and 20 percent CCDS than for cows fed the control diet. Thus, CCDS by itself can be a good feed for dairy cattle. However, we do not recommend feeding as much as 20 percent CCDS because diets including that much CCDS contained more than 0.5 percent phosphorus.
Other distillers products
One will see a growing list of new distillers products available as feeds for livestock in the future because processors continue to improve the efficiency of ethanol production and look for ways to fractionate byproducts resulting from the process. Abdelqader et al. recently completed an experiment feeding the germ that was removed from the corn grain prior to ethanol production. The germ was fed to lactating cows at 0, 7, 14 and 21 percent of ration DM. Inclusion at 7 and 14 percent of DM increased milk and fat yields; however, feeding 21 percent corn germ decreased the concentration and yield of milk fat.
Corn germ from wet milling operations may contain 45 percent or more fat, but feeding trials with that product are limited. A high protein distillers grains product is coming available for evaluation. Ethanol producers are currently evaluating several approaches to remove fat from the coproducts for use in biodiesel. The results will be low fat DGS or other coproducts.
Corn gluten feed
Corn gluten feed (CGF), often fed wet, is a relatively high fiber, medium-energy, medium-crude protein product that can be fed to dairy cattle. The energy value of wet CGF was 92 to 100 percent of the energy value of shelled corn; values were slightly lower for dry CGF. Lactating cows can consume quite large amounts of CGF with acceptable performance. Staples et al. reported linear declines in DM intake and milk yield as amounts of wet CGF increased from at 0 to 40 percent of DM in 50 percent corn silage diets; however, dry matter content of the total diet may have been part of the problem as mentioned earlier regarding the feeding of wet DGS.
Armentano and Dentine observed no reductions in DM intake and milk yield when diets contained as much as 36 percent of ration DM as wet CGF. Wet CGF replaced only concentrates in most of the above studies. When wet CGF replaced up to 35 percent of ration DM as a mix of alfalfa hay, corn silage and corn grain, milk production was greater than when fed the control diet. In experiments that included as much as 45 percent of ration DM as wet CGF, Schroeder concluded that 18.6 percent 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.
Corn gluten meal
Corn gluten meal (CGM) is a high protein (65 percent CP) high RUP (75 percent of CP) 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.
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.
More new and improved distillers products will likely be available to the feed industry in the future. For instance, improvements in fermentation technology already provide DGS today that contains more protein and energy than DGS of previous years. It is also 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. And some products from ethanol production may find their way into human foods and non-food products such as building products and biodiesel. PD
References omitted but are available upon request at firstname.lastname@example.org
—Excerpts from 5th Mid-Atlantic Nutrition Conference Proceedings