Corn Silage Considerations When Feeding Corn Milling Co-Products



Inclusion of distillers grains in dairy diets has been intensely studied for many years. For example, in the classic text titled Feeds and Feeding (1898), W. A. Henry describes a Finnish study published in 1893 which reported that, compared to cows consuming oats, those consuming corn-whiskey distillers grains produced 12% more milk and 9% more milk fat. In a later version of this text, W. A. Henry (1911) estimated an annual production of merely 60,000 metric tons of distillers grains. This is in stark contrast to today when it is estimated that the United States alone produces 13 million metric tons of distillers grains from corn-ethanol production. Type and chemical composition of products available continue to change, and the supply continues to grow, presenting new challenges to the dairy producer and feed industry. With the recent expansion of the ethanol production industry, the feed industry has seen an increase in availability and use of distillers grains. The primary product of the dry milling production process is ethanol; however, approximately one-third of the total dry matter is recovered in the form of co-products, primarily wet or dry distillers grains plus solubles (WDGS and DDGS). Over the last 10 years, a considerable amount of research has evaluated the use of WDGS and DDGS in dairy diets. A portion of this research has improved our understanding of the chemical composition and availability of nutrients in co-products. In turn, this information can be used to help us understand how these feeds can be included in diets and aids in understanding the impact these rations will have on performance.

Corn silage continues to be a major component of rations fed to dairy cattle in the Midwest and Plains states. Because of this, nutritionists often utilize feed analysis data of corn silage as the starting point for ration balancing. More specifically, the quality of corn silage usually dictates how a ration is balanced and what ingredients are included. The aim of this paper will be to summarize recent research that outlines the chemical composition and availability of nutrients in corn milling co-products. The nutritional impact of corn milling co-products in diets containing corn silage will then be discussed.

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Nutrient Availability and Chemical Composition of Distillers Grains

The chemical composition of distillers grains is different from that of the original feedstock used in the ethanol production process. For example, Table 1 lists the chemical composition of corn and corn WDGS and DDGS (note samples of WDGS and DDGS originate from different sources and thus cannot be compared statistically). In Table 1, perhaps the most noticeable difference between corn and WDGS/DDGS is the increased proportion of crude protein (CP) in WDGS/DDGS (29.5/30.5 versus 9.4% CP for WDGS/DDGS and corn, respectively). Logically, the proportion of starch is also much lower in WDGS/DDGS (6.68/5.97%) compared to corn (70.5%). Together, these simple observations support the historical use of WDGS/DDGS as replacements for high protein containing feedstuffs such as canola or soybean meal.

Table 1. Chemical composition of wet distillers grains (WDGS) and dry distillers grains (DDGS) (Dairy One Forage Analysis Lab results, January 21, 2008).
Shelled Corn WDGS DDGS
n1 Mean SD2 n1 Mean SD2 n1 Mean SD2
DM, % 4745 90.1 3.53 1177 28.6 13.0 2914 87.6 8.9
CP, % 4064 9.40 1.63 1171 29.5 12.3 2805 30.4 4.1
ADICP, % DM 1452 0.53 0.99 1119 3.5 2.20 2397 4.8 2.1
NDICP, % DM 1454 0.96 0.33 720 8.11 4.3 790 9.6 3.4
Lignin, % 1655 1.17 0.34 307 5.0 2.0 830 5.3 1.9
ADF, % 2680 3.49 1.5 1088 14.4 5.9 2389 16.7 3.7
NDF, % 2710 9.76 3.0 1091 28.9 10.3 2376 33.3 4.8
Starch, % 1946 70.49 5.13 552 6.68 12.5 1433 5.97 5.39
NFC3, % 2050 76.8 4.33 1046 32.4 19.4 2079 26.0 6.98
Crude Fat, % 2238 4.30 1.26 678 12.1 4.90 2086 13.0 3.0
Ash, % 1869 1.52 0.48 267 5.33 2.37 968 5.93 1.10
Ca, % 2344 0.04 0.12 489 0.08 0.12 1928 0.09 0.13
P, % 2338 0.32 0.10 489 0.85 0.16 1945 0.91 0.14
Mg, % 2322 0.12 0.09 489 0.31 0.07 1920 0.32 0.05
K, % 2325 0.41 0.10 489 0.97 0.30 1920 1.08 0.21
Na, % 1050 0.03 0.17 434 0.14 0.13 1554 0.19 0.19
S, % 1830 0.10 0.09 378 0.54 0.16 1421 0.64 0.18
1Number of samples
2Standard Deviation
3NFC = Nonfiber carbohydrates calculated by difference 100 – (%NDF + %CP + %Fat + %Ash)


Protein contained in the feed can be utilized by rumen microbes. However, the rumen undegradable protein (RUP) portion may bypass the rumen and flow to the small intestine where it is digested and absorbed. Recent research at the University of Nebraska-Lincoln has evaluated both the rumen undegradable protein (RUP) values and the intestinal digestibility of this protein (dRUP) (Kononoff et al., 2007). Using 16-hour in situ incubations, we observed the RUP of DDGS averaged 43.0 % CP, which was higher than soybean meal (28.4 %CP) but not as high as non-enzymatically browned soybean meal (SBM) (75.7% CP). A large proportion of this protein was also digested in the small intestine (86.2 % CP), although it was slightly lower than soybean meal and non-enzymatically browned SBM (98 and 96%, respectively).

In the Midwest, diets that are formulated to contain a high proportion of corn silage usually rely on ingredients such as SBM to supply rumen degradable protein (RDP). In an experiment in which SBM comprises 17% of the total ration, WDGS could act as an effective replacement of protein (Birkelo et al., 2002). Janicek et al. (2008) replaced both SBM and by-pass soy (9% of the total ration), along with several other ingredients, with WDGS in a high corn silage diet and noted an increase in milk production. Alfalfa is low in RUP and, because of this, it is a challenge to meet the cows’ needs for RUP in rations that are high in alfalfa. In fact, it is likely that this is a major reason why inclusion of distillers grains in diets high in alfalfa usually results in an increase in milk yield (Grings et al., 1992).

In addition to ruminal protein degradability, our growing understanding of protein nutrition and utilization has led us to consider the use and supply of individual amino acids (AA) during ration balancing procedures. Limiting AA are defined as those amino acids that are in shortest supply (Socha et al., 2005). The NRC (2001) suggests methionine (MET) is most limiting in rations that depend upon soy or animal protein for major RUP supply. In rations formulated to contain high levels of corn products, such as corn distillers grains and corn silage, the supply of lysine (LYS) is believed to be more limiting (Liu et al., 2000). Using 16-hour rumen incubation, research at the University of Nebraska-Lincoln has demonstrated that the concentration of lysine in the RUP fraction of corn DDGS (1.86% CP) is low. A similar level has been observed in wheat distillers grains (1.16%) (Boila et al., 1994). As a consequence, it is often suggested that diets containing high proportions of corn silage and corn distillers grains may be deficient in LYS. Interestingly enough, a reduction in milk protein yield has rarely been observed. However, it should also be noted that in most published studies, the CP content of the diet was high (i.e., > 17%) and, as a consequence, the supply of LYS to the small intestine may have been adequate even if, in relation to MET, the concentration was low.


It has only been recently that WDGS/DDGS have been extensively thought of as a source of energy to replace forage fiber and nonfiber carbohydrate in dairy diets. Feeding distillers grains to replace corn grain is useful in providing energy in the form of fermentable fiber. Because fiber is digested at a slower rate and less lactic acid may be produced compared to other energy sources such as starch, feeding WDGS/DDGS to ruminants may be useful in reducing the incidence of rumen acidosis (Klopfenstein et al., 2001). Compared to corn, WDGS/DDGS contain a higher proportion of NDF (28.9/33.1 versus 9.76%), and this NDF is not highly lignified; thus, it is also highly digestible. Commercial and publicly available data sets have reported 24- and 48-hour in vitro rumen NDF digestibilities of DDGS to be high (i.e., > 50%). Because fiber is digested at a slower rate than other forms of energy such as starch, feeding corn distillers grains to ruminants may be useful in reducing the incidence of rumen acidosis (Klopfenstein et al., 2001).

The fermentability of fiber in diets high in corn silage is usually quite high and this is linked to an increase in rumen microbial protein yield and ultimately metabolizable protein (Hristov and Broderick et al., 1996). Practically, when WDGS/DDGS and corn silage are used together, nutritionists should be sure to avoid rumen acidosis and track associated risk factors. In doing so, some of the most important factors are concentrations of nonfiber carbohydrates, starch, and sugars. The NRC (2001) committee recommends that ration NFC concentrations should be between 32 and 42% of the diet DM. Users of the CPM-Dairy model may also track the levels of soluble fiber and available NDF which, when fermented, contribute to the rumen acid load (Lanzas et al., 2006).

Effective Fiber

Effective fiber is the portion of the diet that is believed to stimulate rumination, chewing activity, and saliva secretion, all of which are designed to help to maintain healthy rumen function and normal pH levels. When rumen pH levels fall below 6.0, fiber digestion may be impeded, and milk fat levels may become depressed. It is believed that rumen pH is a function of lactic acid and other acid production and is buffered by saliva (Maekawa et al., 2002). Because of this finding, it is a common practice to feed diets of longer particle size, causing a greater amount of effective fiber so salvia production is stimulated. In support of this hypothesis, Krause et al. (2002) noted that the intake of particles > 19.0 mm was negatively correlated with the amount of time rumen pH was below 5.8. However, it is also known that diets should not be excessively long or coarse as they are more difficult to mix and may induce cattle to sort out ration ingredients (Kononoff et al., 2003). When WDGS or DDGS are used to substitute forage in the TMR, chewing activity is believed to be reduced due to the finer particle size. Nutritionists should not necessarily use this logic to infer that feeding co-products will result in lower rumen pH. In fact, it is likely that diets may be balanced so that the inclusion of co-products will not influence rumen pH. When evaluating a diet to determine a possible risk of subclinical acidosis, it is important to consider both levels of fiber and non-structural carbohydrates, along with their associated fermentability (Yang et al., 2001).

Using the Penn State Particle Separator, at least 5 to 10% of the particles should be at least 19.0 mm long, and the diet should contain 26 to 30% NDF. General recommendation suggests that rations should contain 30 to 50% of the particles between 8 and 19.0 mm. Diets which are high in both corn silage and co-products generally have less material within this range. If this is the case, poor-quality roughages such as chopped straw or grass can be added to increase effective fiber levels.

Feeding Considerations

Wet and Dry Distillers Grains Plus Solubles

As mentioned earlier, distillers grains may be available in either a wet or dry form, and the nutrient content, when expressed on a dry matter basis, is similar for both (Table 1). One possible major difference between these forms may be due to the RUP portion being higher in the dry form (Firkins et al., 1984). Although it is generally believed that there is little difference in milk production when animals are fed either form, beef feedlot studies have demonstrated that rations containing wet distillers grains are consumed in lower quantities and result in greater feed efficiencies than those containing dried distillers grains (Ham et al., 1994). Unfortunately, less research has investigated possible differences in milk performance. In one study in which lactating dairy cattle were fed diets containing 15% (DM basis) of either wet or dry forms, no differences were observed in milk production, composition, fiber digestibility, or efficiency of milk production (Al-Suwaiegh et al., 2002).

When deciding which form may fit best, producers should evaluate several factors including distance from plant of origin, anticipated feeding rate, on-farm storage facilities, and handling equipment. Because a wet product may not be stored as long and is usually associated with high shipping charges, dried forms may be most feasible for feeding if a plant is not located near the farm. However, this also increases the price of the feedstuff. If the farm is located near a plant, wet forms may be cost effective, but producers should be mindful of the fact that the rate of spoiling is also dependent upon the feeding rate and environmental temperature. Generally speaking, wet loads should arrive at least weekly to ensure the pile is “fresh.” There continues to be interest in ensiling feeds such as wet distillers grains as a method to eliminate oxygen exposure and ultimately reduce feed spoiling and loss. Additionally, a number of commercial direct application preservative products may be useful in extending shelf life of these feeds, but producers should be mindful of these added costs.

Feeding Levels and Production Responses

Recently, a number of investigators have evaluated the effects of increasing levels of corn-ethanol distillers grains in replacing both forages and concentrates (Powers et al., 1995; Owen and Larson, 1991; Leonardi et al., 2005). Research suggests that the addition of distillers grains to dairy diets high in corn silage usually results in a modest increase in DMI (Nichols et al., 1998; Powers et al., 1995; Owens and Larson, 1991; Janicek et al., 2008); however, this is not observed in all cases (Leonardi et al., 2005; Schingoethe et al., 1999). Nevertheless, the increase in DMI is somewhat predictable, given that intake is influenced by feed particle size and digesta passage rate (Beauchemin et al., 2005), both of which have been demonstrated to increase in diets containing milling co-products (Boddugari et al., 2001).

In published studies evaluating corn DDGS as a protein supplement, milk production was observed to be either unaffected (Clark and Armentano, 1993; Owen and Larson, 1991) or increased (Powers et al., 1995; Nichols et al., 1998). The high level of fat is one factor believed to affect milk fat synthesis and, as a result, the inclusion of DDGS should be limited in dairy diets. This effect was not observed by Leonardi et al. (2005), who evaluated the effects of increasing levels (up to 15%) of DDGS and the addition of corn oil to the control diet. Nonetheless, when co-products are included at increasing amounts, they will make major contributions to the overall rumen fat load. Consequently, a nutritionist considering increasing the proportion of co-products should reduce the inclusion level of high fat ingredients such as cottonseed.

It is impossible to recommend an optimal inclusion level for distillers grains or other co-products, as it depends upon many factors including price and nutrient content of all available feedstuffs. A number of investigators have evaluated the effects of increasing levels of distillers grains in replacing both forages and concentrates (Powers et al., 1995; Owen and Larson, 1991; Garcia et al., 2004; Kalscheur et al., 2004; Leonardi et al., 2005). Conservative estimates from these studies suggest that 15 to 20% of the ration DM may easily be included in a properly formulated ration for a lactating cow. Further evidence also suggests that even greater amounts of DDGS may be fed (Janicek et al., 2006) without sacrificing production. However, at these levels and often in those high in alfalfa, the diet may contain excessive levels of N that is poorly utilized, resulting in increased N excretion.

CPM-Dairy Model: Corn Silage and DDGS

Table 2 lists two high corn silage dairy rations that were formulated using least cost solutions and the CPM-Dairy model. These rations differ in the amount of DDGS included, 0 or 15% of the diet DM. A 15% inclusion level of DDGS replaces a portion of the forage, ground corn, and protein ingredients. The aim of formulating this diet was to maintain metabolizable protein (MP) and metabolizable energy (ME) allowable milk at 75 pounds but to do so with less energy from corn grain and less protein from soy. In practice, one of the most challenging things for a nutritionist may be to pay less attention to thumbnail rules of starch or nonfiber carbohydrate (NFC). Recent research has demonstrated similar diets may be formulated to be successful (Janicek et al., 2008). For this low NFC ration to be successful, the availability of fermentable fiber is critical as a greater proportion of energy will originate from fermentable fiber. Thus, good harvesting techniques and the use of highly digestible and/or low lignin hybrids should prove useful in this circumstance. Currently, the University of Nebraska-Lincoln employs the technique of Tilly and Terry (1963) to evaluate the fiber digestibility of corn silages fed in research projects. We categorize corn silage as highly digestible and good-quality when in vitro 30-hour incubations result in NDF digestibility greater than 50% (Gehman et al., 2008). Feeding high proportions of such corn silage may result in large contribution of fermentable carbohydrate and ultimately energy supply to the animal.

Table 2: Dairy ration with and without dried distillers grains plus soluble (DDGS).
Ration Inclusion
0% DDGS 15% DDGS
Ingredient, %DM Lb As Fed (DM) Lb As Fed (DM)
DDGS1 0.0 (0.0) 7.9 (7.0)
Corn silage 30.1 (12.0) 27.6 (11.0)
Alfalfa haylage 13.7 (4.1) 8.4 (2.5)
Alfalfa hay 2.8 (2.5) 4.4 (4.0)
Brome hay 3.3 (3.0) 4.4 (4.0)
Ground corn 10.68 (9.4) 8.4 (7.4)
Soybean meal 4.5 (4.1) 3.4 (3.1)
By-pass Soy 1.9 (1.8) 0.84 (0.75)
Cottonseed 1.2 (1.0) 0.0 (0.0)
Soybean hulls 6.5 (6.0) 4.1 (6.4)
Vit/Min Mix 1.4 (1.4) 1.6 (1.6)
Nutrient Concentration
DMI, lb/d DM 45.4 45.5
CP, % DM 17.5 18.2
P, % DM 0.36 0.40
S, % DM 0.21 0.26
Starch, % DM 26.0 23.4
Lignin, % DM 3.1 3.3
EE, % DM 3.33 4.91
NDF, % DM 34.8 35.1
CPM-Dairy Predictions
Allowable Milk, kg
          Metabolizable Energy
          Metabolizable Protein


Bacterial CP Yield
          NFC Bacteria, g
          Fiber Bacteria, g
          Total, g


          NDF, % DMI
          Starch, % DMI


ME, mcal/lb 1.17 1.17
Bacterial MP, % MP 53.4 49.4
Lys:Meth 3.5:1 3.21
Duodenal 18:1 T Flow, g 45.1 84.4
1Chemical composition as described by Greenfield Ethanol, Varennes, QC (CP = 30.3%, Fat = 15.8%, NDF = 33.8%, Ash, 6.13%, P = 0.98%, S = 0.67%).

The CPM-Dairy model is also useful because it allows the user to strive to optimize rumen fermentation and contribution of rumen bacterial crude protein to MP supply. Table 2 also lists the predicted rumen microbial crude protein which is similar between diets (511 and 493 g for 0 and 15% DDGS). Rumen N balance may also be evaluated using the CPM-Dairy model. Rumen bacteria that ferment NFC use both ammonia and peptides as N sources. In contrast, those that ferment fiber are believed to utilize ammonia (Russell et al., 1992). Generally speaking, the predicted rumen N pools of these components should be at least 100%; however, up to 150% may need to be tolerated to optimize and solve the least cost solution. Given that DDGS are a rich source of P, S, and protein, these nutrients are expectedly higher in the diet containing DDGS. Lastly, peNDF in these rations was maintained at 22.2% by adding a low protein, long roughage in the form of grass hay.

Summary and Conclusions

Feed by-products from the dry milling industry will continue to be common and cost-effective ingredients in dairy diets. Assuming the price of distillers grains will continue to remain lower than corn grain and soybean meal, it is easy to predict that rations including these feeds will be cheaper. This economic benefit underscores the growing importance of understanding how co-products may be included in dairy diets high in corn silage. Current research suggests dairy rations may be easily formulated to contain 15% DDGS. When including distillers grains in dairy diets, nutritionists should ensure that the diet contains adequate levels of digestible NDF and effective fiber and should be mindful of the high concentration of fat in this feedstuff.

Author Information

P.J. Kononoff
K.J. Machacek
University of Nebraska-Lincoln


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Henry, W.A. 1911. Feeds and Feeding. M.J. Cantwell, Printer, Madison, Wis.