Distillers grains with solubles (DG) is a unique feedstuff providing protein, fat, highly digestible fiber and minerals, all of which can be utilized in dairy rations. Distillers grains with solubles are coproducts from the manufacture of ethanol. Although other cereal grains, such as sorghum, wheat or barley, can be used to produce ethanol, the predominant cereal grain used in the United States to produce ethanol is corn (Zea mays).
During the dry milling process used for ethanol production, the entire corn kernel is used in the fermentation process. The corn is cleaned and then hammer milled to a medium-coarse to fine-grind meal. The resulting flour is combined with water to form a slurry, and enzymes are added to convert the starch in the kernel to sugar. The resulting mash is then cooked and sterilized to kill unwanted bacteria.
Once the mash is cooled, yeasts are added to the mash and the sugar is converted to ethanol and carbon dioxide. The ethanol is then extracted in the distillation process, and the remaining water and solids are collected and referred to as whole stillage.
Whole stillage can be pressed, but more commonly it is centrifuged to separate the coarse solids from the liquid. The liquid is referred to as distillers solubles, also known as thin stillage. The thin stillage can be concentrated in an evaporator to become condensed distillers solubles (CDS), also referred to as syrup. The coarse solids collected from the centrifuge are known as wet distillers grains. Wet distillers grains and CDS are combined and dried to form dried DG.
Nutrient composition of DG
Knowing accurate nutrient composition of DG is critical when formulating diets for livestock. Laboratory testing of purchased DG is highly recommended, although not always practical for every shipment. This information may also be provided by the ethanol plant.
Nutrient content of DG is influenced by factors such as the type of grain, grain quality, milling process, fermentation process, drying temperature and the amount of solubles blended back into the wet DG at the time of drying.
Distillers grains being fed in dairy cow diets today contain more protein and energy than older book values. The newest dairy National Research Council recommendations (NRC 2001) list crude protein (CP) at 29.7 percent for DG with solubles, a number that is close to reality. Average CP for DG is around 30 percent, but studies illustrate CP ranging from 27 to 35 percent is not unusual.
Of particular interest to dairy nutritionists is that DG is a good source of rumen-undegraded protein (RUP). Most reported values range from 47 percent to 57 percent RUP. However, more recent research suggests the RUP may be higher. Research conducted at South Dakota State University determined the RUP of five different sources of dried DG and found that RUP varied from 63.5 to 78.0 percent. Some of the readily degradable proteins in corn are degraded in the fermentation process, so the protein remaining in DG will be higher in RUP than in the original corn.
This study also evaluated one wet DG sample and found that wet DG had a lower RUP value (54.7 percent) compared to the dried DG samples. The lower RUP value attributed for the wet DG was likely due to the fact that drying was not required.
Rumen-undegraded protein values for DG that are very high (e.g., greater than 80 percent of CP) are usually a result of heat-damaged, indigestible protein. Heat-damaged protein would be indicative of a high acid detergent insoluble crude protein (ADICP), although there is not a clear relationship between ADICP and protein digestibility in DG as there is in other types of feeds.
The quality of protein in DG can be good, although as with most corn products, lysine is the first limiting amino acid. Since lysine is very sensitive to heat, it is believed that extensive heating, or darker distillers grains, will have reduced concentrations of digestible lysine.
Some researchers speculate the DG available today may contain more energy than indicated by the NRC book values. Although no work has been published using dried DG, Birkelo et al. determined the energy value of wet DG for lactating cows. In this study, digestible energy (DE), metabolizable energy (ME) and NEL of wet DG were 4.09, 3.36 and 2.27 Mcal per kilogram of DM, respectively. These energy values are 7 to 11 percent and 10 to 15 percent higher than previously published values reported in the 1989 and 2001 NRC.
Neutral detergent fiber (NDF) (39 percent) and acid detergent fiber (ADF) (19 percent) can vary significantly. Some newer DG has been reported to have concentrations of NDF and ADF considerably lower than NRC values, 27.1 and 14.4 percent, respectively.
One concern for nutritionists is that the level of fat in DG can vary greatly, and it can be higher than 12 percent, much higher than values reported in the NRC (2001). Distillers grains contain high levels of unsaturated oil, predominantly linoleic acid, reflecting the composition of corn oil. Research at South Dakota State University showed fat concentration was 13.1 and 12.1 percent for dried and wet DG respectively.
It should be noted that the method of fat analysis can significantly affect this value. A study from Wisconsin measured fat at two labs and found two significantly different results (10.5 versus 16.4 percent fat). These differences were attributed to different ether extract assays used in each lab.
High levels of unsaturated fatty acids are a concern when balancing diets for lactating dairy cows because they can cause increased incomplete biohydrogenation in the rumen, potentially resulting in milk fat depression.
Although complete fermentation of starch is desirable to increase ethanol production, there is usually some starch remaining in DG. During the 1980s and ’90s, starch in dried DG was measured to be 10 to 15 percent. Recently analyzed samples of DG resulted in 5 percent starch. Improved efficiency in fermenting more of the starch in the corn to ethanol is most likely the reason for these changes in the composition of DG.
Environmental concerns regarding excessive phosphorus have increased the awareness of phosphorus concentrations in DG. Most DG contain between 0.65 and 0.95 percent phosphorus. High-producing dairy cows often need some supplemental phosphorus; therefore lower inclusion levels of DG usually replace inorganic sources. The greatest concern of using DG will be in regions of the United States where soils are already high in phosphorus.
The other mineral that can be highly variable is sulfur. High sulfur levels in feed and water can result in central nervous system disorders which can lead to poor performance or death. This is rarely reported in dairy cattle, but it has been reported in beef cattle.
Production response of cows fed DG
Twenty-seven studies evaluating the addition of DG to dairy cow diets have been reported in the United States since 1982. Of these studies, 19 evaluated the inclusion of dried DG in dairy cow diets. The remaining studies evaluated the inclusion of wet DG to dairy cow diets. Prior to the late 1990’s, many of the experiments evaluating DG used DG originating from production of drinking alcohol. Since that time, all DG evaluated in dairy cow studies have used DG originating from modern fuel-ethanol plants.
Since DG was first recognized as a good source of protein, most research was developed to test DG as an alternative source of CP and RUP for dairy cow diets. More recently, research is focusing on DG as a source of energy from the fat and highly digestible fiber found in DG.
Distillers grains as a protein source
Most previous studies replaced soybean meal or a combination of soybean meal and corn when including DG into dairy cow diets. Feeding iso-nitrogenous diets, Palmquist and Conrad found different milk production responses in Holstein versus Jersey cows. Jersey cows responded positively to the addition of 24 percent dried DG; however, Holstein cows were unaffected.
Van Horn et al. reported a reduction in milk yield and milk protein percentage when feeding 22.5 and 41.6 percent of the diet DM as dried DG in diets formulated to provide 14 and 18 percent CP. The dried DG in this experiment contained high levels of acid detergent insoluble nitrogen (ADIN), and these authors attributed the loss of production as a result of high ADIN content.
Weiss et al. fed a dried DG produced from a blend of 65 percent barley and 35 percent corn. In this experiment, dried DG was fed up to 12.9 percent of the diet DM and did not affect intake, milk production or milk composition.
Owen and Larson reported the results of a study comparing dried DG and soybean meal in diets for early lactation cows. Cows increased in milk production when dried DG was fed at 18.8 percent of the diet DM, most likely due to increased dietary RUP, but milk production decreased when dried DG was included at 35.8 percent of the diet DM. The authors concluded that lower protein digestibility and lysine levels contributed to the decreased performance of cows fed the 35.8 percent DG diet. The decrease in milk protein percentage on the dried DG diets in this study indicated available lysine may have been deficient in these corn silage-based diets.
Powers et al. compared three different sources of dried DG with soybean meal at two dietary crude protein concentrations (14 and 18 percent). Designated by source, DDGS1 and DDGS2 were light in color and were lower in ADIN, whereas DDGS3 was dark in color with a higher ADIN. Dry matter intake (DMI) was not affected by the source of dried DG or by the CP level. Cows fed DDGS1 and DDGS2 produced more milk than cows fed 0 percent DG (soybean meal diet) and the DDGS3 diet. In addition, cows fed dried DG incorporated into the diet at 26 percent of the diet DM produced more milk than cows fed 13 percent.
More recently, Kleinschmit et al. compared three different sources of dried DG from modern fuel-ethanol plants. The three DG sources were processed differently with the intent to reduce protein damage, thereby improving the protein quality of the DG feedstuff. Dry matter intake did not change, but cows fed diets containing DG (at 20 percent of the diet) produced more milk than cows fed the control diet containing no DG. Milk fat percentage was not changed, but milk protein percentage declined from 3.28 to 3.16 with the addition of DG. The source of DG had very little impact on overall lactation performance.
Since DG is often used as a source of RUP in dairy cow diets, Pamp et al. investigated the effect of source and level of RUP in lactating diets by comparing dried DG to soybean protein. Soybean protein included a combination of SBM 44 percent, extruded soybeans, soyhulls and expeller soybean meal. These feeds were combined together to create a blend similar in nutrient content to DG. Diets were formulated to contain 5.3, 6.8 and 8.3 percent RUP (DM basis) and included 0, 11 or 22 percent dried DG as the source of the RUP.
Milk production increased with the addition of RUP and was greater for cows fed diets containing DG versus soybean protein. Milk fat percentage was not affected by addition of RUP or by source of RUP, but milk protein percentage was greater for cows fed DG compared to cows fed soybean protein (2.85 versus 2.80 percent). This research supports the conclusion that DG can replace soybean protein as a source of RUP without reducing milk production and milk protein percentage if diets are formulated properly.
Distillers grains with solubles are a good source of methionine, but are low in lysine, therefore supplementation of rumen-protected lysine would theoretically allow one to maximize the use of DG in dairy cow diets. Nichols et al. reported an increase in milk production when cows were fed a ruminally protected lysine and methionine product in diets where dried DG was included at 0.25 percent of the diet DM.
However, in a following experiment, Liu et al. did not observe increased milk production when ruminally protected lysine and methionine were fed to cows with 18.85 percent dried DG included in the diet. Results of experiments with added amino acids by ruminally protected amino acids or by feedstuffs such as blood meal have been variable. In general, dried DG is a good-quality protein source that can often be used as the only source of supplemental protein in properly formulated diets.
Distillers grains as a fiber source
Research has also been conducted to evaluate the ability of DG to replace a portion of the forages found in dairy cow diets. Since DG is high in NDF, it is tempting to replace some of the NDF provided from forages with the NDF from DG. Clark and Armentano tested the effect of replacing alfalfa NDF with NDF from dried DG on milk production and composition. Replacing 12.7 percent of the alfalfa DM with dried DG resulted in both milk production and milk protein percentage increases. Although the proportion of alfalfa in the diet dropped from 44 percent to 31 percent of the diet DM when dried DG was added, milk fat production was not altered.
One concern about replacing forage NDF in dairy diets is that the removal of physically effective fiber may alter normal rumen function causing milk fat depression. In a recent study, Cyriac et al. evaluated the replacement of forage fiber from corn silage with non-forage fiber from dried DG in dairy cow diets. Diets were formulated to include 0, 7, 14 and 21 percent dried DG replacing an equal portion of corn silage. The basal diet included 40 percent corn silage, 15 percent alfalfa hay and 45 percent concentrate. Diets contained 15 percent alfalfa hay across all four diets.
Dry matter intake increased as DG increased in the diets, but milk production remained the same. Milk fat percentage, however, decreased (3.34, 3.25, 3.04 and 2.85 percent) and milk true protein increased (2.82, 2.90, 2.93 and 3.04 percent) as the percentage of DG increased in the diet.
To prevent changes in milk fat composition, sufficient physically effective fiber from forage must be included when formulating diets with DG.
Wet versus dried DG
Only two direct comparisons of wet DG versus dried DG have been conducted. Al-Suwaiegh et al. fed lactating dairy cows wet and dried DG at 15 percent of the diet DM. No differences in dry matter intake, milk production and milk composition between wet and dried DG were found, indicating no advantage of one form over the other.
More recently, Anderson et al. fed iso-nitrogenous diets formulated to include wet or dried DG at 0, 10 and 20 percent of the diet (DM basis). Milk production increased with the addition of DG in either form (wet or dried) compared to the control diet containing 0 percent DG. Both milk fat and milk protein percentage were similar for cows fed the control compared to DG; however, cows fed the wet DG diets resulted in greater milk fat and milk protein percentages than cows fed dried DG.
Both of these studies demonstrate that wet DG can be successfully formulated in a dairy cow diet without decreasing milk production and milk fat percentage.
High inclusion rates of DG
In practical application, it is generally accepted that DG can be included in dairy cow diets at 10 percent of the diet DM without negatively affecting milk production and composition. But the overall question remains: How much distillers grains can be included into dairy cow diets, and what effect does it have on milk fat and protein composition, and overall milk production?
Several studies have been conducted evaluating the level of inclusion of DG in dairy cow diets. Hippen et al. conducted a study which included dried DG up to 40 percent of the diet DM. Diets were formulated to include dried DG at 0, 13, 27 and 40 percent of the diet replacing other concentrate feeds. These diets were not iso-nitrogenous, and CP percentage increased from 16.5 to 18.9 percent. Intake increased with the addition of DG at 13 percent, but declined as DG was further included in the diets.
Milk production mirrored these results and was highest when DG was included at 13 percent of the diet, but declined as DG was further added to the diet (40.7, 41.7, 39.1, 36.3 kilograms per day). Milk fat percentage was lower for cows fed DG in the diets compared to cows fed control diet (3.16 versus 3.40 percent) but did not differ across inclusion level. Milk protein percentage was not affected by inclusion of DG.
A similar experiment evaluated the effect of including wet DG in dairy cow diets. This study included wet DG at 10, 20, 30 or 40 percent in iso-nitrogenous diets (18 percent CP) replacing other concentrate feeds. When wet DG was included at a level greater than 20 percent of the diet, DMI and milk production declined. At the high inclusion levels (30 and 40 percent DG), DM concentration of the total diet was only 40 to 46 percent. The authors concluded that gut fill of cows fed the high wet DG diets may have limited intake and consequently milk production. Milk fat and protein were not affected by inclusion rate.
Because alfalfa is a good source of lysine, it was thought that alfalfa-based diets may be a better forage base to which to add DG. Grings et al. added dried DG to alfalfa-based diets at 0, 10.1, 20.8 and 31.6 percent of the diet DM. These diets were formulated to provide 13.9, 16.0, 18.1 and 20.0 percent CP. Although DMI did not vary across diets, milk yield and milk protein percentage increased linearly with increasing levels of DG.
It should be noted that dietary CP percentage of these diets was not kept constant; therefore as DG increased in the diet, so did CP percent. Cows fed the 31.6 percent DG diet produced the same amount of milk as those fed the 20.8 percent DG diet. Cows fed the 31.6 percent DG diet were fed in excess of their protein requirement. Therefore, no additional production response resulted at this level of DG inclusion.
Meta-analysis of DG studies
In order to assess the impact of inclusion of DG on lactation performance, a meta-analysis of previous feeding studies was conducted. Twenty-three studies investigating the inclusion of DG in dairy cow diets were compiled into a database with 96 treatment comparisons. Overall, DMI increased when DG was included up to 20 percent of the dry matter (DM) in dairy cow diets. However, DMI was also affected by form of the DG. Whereas intake of cows fed wet DG was highest at lower inclusion levels (less than 20 percent of the DM), cows fed dried DG increased DMI up to the 30 percent inclusion. Decreases in intake at higher inclusion levels may be caused by higher dietary fat concentrations, or in the case of wet DG, high dietary moisture concentrations.
Milk production was not affected by form, but there was a curvilinear response of increasing DG in dairy cow diets. Cows fed diets containing 4 to 30 percent DG produced the same amount of milk, approximately 0.4 kilograms per day greater than cows fed diets containing no DG. When cows were fed the highest inclusion rate (greater than 30 percent), milk yield decreased. Cows fed wet DG decreased in milk production when included in the diet greater than 20 percent. This was most likely related to decreased DMI.
Milk fat percentage varied among inclusion levels and was not significantly affected by inclusion level or form. The current dataset does not support the theory that feeding DG results in milk fat depression. Many factors play an important role in causing milk fat depression. When formulating diets it is important to include sufficient fiber from forages in order to maintain rumen function.
Distillers grains provide 28 to 44 percent neutral detergent fiber, but this fiber is finely processed and rapidly digested in the rumen. As such, fiber from DG is not considered ruminally effective fiber and should not be considered equal to forage fiber.
High levels of fat provided from DG may also impact rumen function leading to milk fat depression, but it is often a combination of dietary factors which lead to a significant reduction in milk fat percentage.
Milk protein percentage was not different for cows fed diets with 0 to 30 percent DG inclusion, and the form of the DG did not alter composition. However, milk protein percentage decreased 0.13 percentage units when DG was included at concentrations greater than 30 percent of the diet compared to cows fed control diets. At the higher inclusion levels, DG most likely replaced all other sources of protein supplementation. At these high levels of inclusion, lower intestinal protein digestibility, lower lysine concentrations and an unbalanced amino acid profile may all contribute to lower milk protein percentage.
It should be noted the lower milk protein percentages were most evident in studies conducted in the 1980s and 1990s. Newer studies are not as consistent in showing this effect. Lysine is very heat sensitive, and it can be negatively affected by processing and drying. Improved processing and drying procedures in the newer fuel-ethanol plants may have improved amino acid quality of the product.
Distillers grains with solubles is an excellent source of protein and energy for lactating dairy cows. Research suggests that DG can replace more expensive sources of protein, energy and minerals in dairy cow diets. Because DG can be highly variable, it is recommendedit be tested to determine exact nutrient composition in order to properly formulate diets.
When balancing diets with DG, care must be taken to provide sufficient physically effective fiber to maintain normal rumen function and prevent milk fat depression. Nitrogen and phosphorus concentrations in DG-based diets also need to be monitored to prevent excessive losses to the environment. As technology improves, new ethanol coproducts will be developed and become available to livestock producers. Current recommendations for feeding DG to dairy cows would be to include DG up to 20 percent of the diet DM. PD
References omitted but are available upon request at email@example.com.
—From 2006 Penn State Dairy Cattle Nutrition Workshop Proceedings
More information on feeding distillers grains to dairy cattle can be found at http://dairysci.sdstate.edu/publications/topic.cfm Select “Distillers Grains” from the topic menu.