Ethanol is produced when starch in corn grain is fermented. Most other constituents in the grain remain unchanged. The end product of the corn is distiller’s grains or DDGS (distiller’s grains with solubles). The DDGS retain the original fatty acids, protein, and phosphorus. In addition, variability in the grain nutrient content used in the fermentation process and the actual process itself results in a feed with variable nutrient content. Distiller’s grains can be fed either in the wet (less than 25 percent dry matter) or dry (greater than 85 percent dry matter) form. Wet DDGS are difficult to store and must be fed within a few days of production. The wet DDGS can be the most cost-effective, however, if used close to where they are produced.
Research by Schingoethe (2007) with dairy cattle has indicated that DDGS can be up to 20 percent of the ration dry matter without problem, and as much as 30 percent in some situations. For lactating cows, this maximum will usually be between 6 percent to 13 pounds of 90 percent dry matter (10 percent moisture) distiller’s grains. Table 1 shows the nutrient content expressed on a dry basis for corn and DDGS according to the 2001 National Research Council (NRC) and Weiss and co-workers from Ohio State.
|Table 1. Nutrient composition of shelled corn and DDGS|
|Crude protein, %||9.4||29.7|
|Starch, % (Weiss et al)||70.0||4.0|
|Net energy, mcal/lb.||0.95||0.90|
|Neutral detergent fiber, %||9.5||38.8|
Because DDGS contain no or little starch and more protein, fat, and phosphorus than corn, ration reformulation is needed to adjust the amounts of forage, grain, protein supplement, and mineral additive. For dairy cattle, the main issues with feeding distiller’s grains are protein concentration and quality, fat content, and phosphorus concentration.
Distiller’s grains are a relatively high-protein feed with approximately 30 percent of the dry matter as protein according to the NRC (2001). Ten pounds of DDGS would supply 2.7 pounds of protein. In many rations, DDGS will substitute partially for soybean meal, which is the most common protein source for dairy cattle. The protein in DDGS is more resistant to rumen degradation than solvent-extracted soybean meal, but in some cases where there is extreme heating of DDGS during drying, there can be reduced protein digestibility. The color of the product does give an indication of heat damage, with dark brown and black being indicators of reduced digestibility. A laboratory test for heat damage should be conducted to verify potential problems before feeding.
In situations where high-protein legume hay or silage is the forage source, the protein in DDGS may be excessive, especially if the maximum is included. Processes do vary and some DDGS will have more than 30 percent protein. Therefore, if no ration adjustment is made when including DDGS, overfeeding protein is a possibility, with possible air- and water-quality impact.
The amino acid lysine is low in all corn products and consequently, rations containing DDGS with corn silage and corn grain would possibly benefit from lysine supplementation. Under these conditions the 20 percent inclusion rate may be excessive.
Another possible limitation is the fat or oil content of DDGS. The NRC lists DDGS as containing 10 percent fat in the dry matter. Adding 10 pounds of DDGS results in 0.9 pound of oil. Unsaturated fats such as that found in corn grain and DDGS are especially a problem with cattle if fed in excess. Unfortunately, this fat is readily available in the rumen and if present in excess, it can interfere with rumen fermentation. Ruminants can tolerate up to 5 percent to 6 percent of the total ration dry matter as fat from typical feed ingredients. If higher fat levels are desired, it is advisable to use rumen protected fats.
If feeds such as whole cottonseeds or soybeans (20 percent fat) are fed, DDGS should be fed at less than the maximum of 20 percent inclusion rate because the maximum amount of fat would be exceeded in the formulation. If rumen protected fat supplements such as Energy Booster or Megalac are used, fat levels of 5 percent to 7 percent of the ration dry matter are tolerated reasonably well. Excessive fat in the ration can result in reduced dry matter intake, milk production, milk fat percentage, and milk protein percentage.
According to the NRC (2001), DDGS contain 0.83 percent of the dry matter as phosphorus (P). Ten pounds of distiller’s grains would contain 0.0747 pounds of P or 34 grams. Distiller’s grains typically will substitute for soybean meal (0.7 percent P), corn (0.3 percent P), and silage (0.2 percent P) in varying proportions depending on the type of silage (corn vs. legume). The resulting reformulated ration balanced for energy and protein would contain at least an extra 10 grams of P when 10 pounds per cow of DDGS is included. Therefore, there can be an extra 1 gram P per 1 pound DDGS inclusion. Typical requirements for P in lactating cows are 60 to 90 grams per day (Hanigan, 2006). Research indicates that after the P requirement is reached, the excess will appear in the feces. Land application of manure adds P to the soil and any in excess of crop requirements can potentially be washed into waterways, becoming a source of pollution resulting in algal blooms and poor water quality. Also, problems with inadequate land area to spread manure can result on farms where phosphorus- based nutrient management plans are in effect.
If distiller’s grains substitutes for other high-P feeds such as cottonseeds (0.6 percent P), brewer’s grains (0.67 percent P), wheat bran (1.18 percent P), wheat middlings (1.02 percent P), or corn gluten feed (1.0 percent P), there may be little net change and in some cases an actual reduction in P in the ration. However, the P requirement for lactating cows would normally be exceeded with these type rations and manure P levels increased. The P requirement for lactating cows is less than 0.4 percent of ration dry matter. Although forages are usually considered low P sources, notice in Table 2 that rye silage and intensively managed pasture can have more P than other forages.
The question arises as to what can be done when the phosphorus content of the ration is excessive and no inorganic sources are included in the ration. Some feeds are identified in Table 2 that are low in phosphorus (0.20 percent P or less). Some of these are readily available such as citrus pulp, cottonseed hulls, and soybean hulls. Others may have application under certain circumstances and limitations. In conclusion, to manage phosphorus content of rations, it is necessary to analyze phosphorus levels and look for alternative feeds in some cases.
|Table 2. Crude protein (CP), fat, and phosphorus content of selected feeds (NRC 2001)|
|Alfalfa hay, immature|
|Alfalfa hay, mature|
|Grass hay, immature|
|Grass hay, mature|
|Pasture, intensively managed|
|Cottonseed meal, solvent|
|Peanut meal, solvent|
|Soybean meal, solvent|
|Fish meal, menhaden|
|Brewers grains, dry|
|Brewers grains, wet|
|Corn gluten feed|
|Low P feeds|
|Sugar beet pulp|
National Research Council. 2001. Nutrient Requirements of Dairy Cattle. National Academy of Science, Washington, D.C.
Schingoethe, David J. 2007. Use of Ethanol Distillers Byproducts in Lactating Dairy Cow Diets. Proceedings of the 5th Mid-Atlantic Nutrition Conference, pages 100-108.
Hanigan, Mark D. 2006. Excel Spreadsheet for Calculating P Requirements of a Herd, www.vtdairy.dasc.vt.edu/spreadsheets/P Requirement Calculations.xls
Weiss, Bill, Maurice Eastridge, Dianne Shoemaker, and Normand St-Pierre. Distillers Grains. The Ohio State University Extension. DAIReXNET, www.extension.org/pages/Distillers_Grain
Virginia Cooperative Extension materials are available for public use, reprint, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.
May 1, 2009