Overview of Distillers By-Products

The increased acceptance of ethanol as an additive to petroleum fuels has resulted in a significant increase in the volume of distiller’s by-product ingredients available to the feed manufacturer. Most soybean growers produce both corn and soybeans. They are pleased with the increased use of corn and corn by-products, but become concerned as the corn by-products replace soybean meal in livestock and poultry rations. This review will overview the feed use of corn by-products in livestock and poultry rations.

The corn dry-milling process has been used by the distilling industry for many years. The process involves grinding of the shelled corn; adding water; adjusting the pH of the slurry and temperature with the addition of amylase enzymes to hydrolyze the cornstarch to simple sugar (dextrose); a yeast is used in the fermentation process to convert the dextrose to ethanol and carbon dioxide. The corn’s fat and fiber during the fermentation process remains unchanged and is concentrated as the starch is converted to ethanol. The ethanol is stripped after fermentation. The fermented material (stillage) is centrifuged to remove the liquid, which is recycled in the process or concentrated in the evaporator to become corn condensed distillers solubles. The solids from the process (corn distillers dried grains) are dried in a rotary dryer. In some processes the corn distiller’s dried grains (DDG) are combined with corn condensed distiller’s solubles, dried and marketed as corn distiller’s dried grains with solubles (DDGS).

DDG and/or DDGS recovered from the process contain about a three-fold increase in the non-starch nutrients contained in the shelled corn raw material. Some of the corn protein is digested during microbial fermentation, resulting in an amino acid pattern in the DDGS being a combination of the corn and microbial protein. The yeast fermentation process also increases vitamins in DDGS. A comparison of the composition of corn, DDGS and soybean meal is contained in the table.

The usefulness of any feed ingredient is dependent on several factors; the most important are nutrient composition, price and availability of the feed ingredient. Nutritionists program computers with information on the ingredient’s composition and price to formulate rations that meet the animal’s nutrient requirements for efficient performance. Computers evaluate ingredients on the basis of providing nutrients at least-cost to meet the nutrients programmed for the feed being formulated. Therefore, DDGS and soybean meal must compete on the basis of composition and price.

The value of DDG and DDGS compared to soybean meal is species dependent, meaning that some species (beef cattle and dairy) can use greater amounts than other species (swine and poultry). Considerable research has been conducted to clarify the levels of the various ingredients that can be included in various rations. Some general conclusions follow:

Beef Cattle:
Distiller’s by-products are sources of energy and protein that can be used in beef feeding operations. The primary value of DDG and DDGS in beef cattle rations is the high level of bypass protein in these ingredients. Soybean meal generally contains 25-30% bypass protein, whereas, DDG and DDGS will contain about twice this level. The level of bypass protein becomes important in formulating rations that need high levels of bypass protein. Feed manufacturers can formulate protein supplements by combining DDG or DDGS with urea to equal the feeding value of soybean meal. Usually the distiller’s by-products are significantly less costly compared to soybean meal.

Feeding levels of 10-20 percent are common; recently research at the University of Illinois has reported that DDG can be included in beef rations up to 50 percent. The Illinois research indicates higher levels can be fed if the price of the DDG is competitive with other ingredients. The composition of distillers by-products are not the limiting factor to greater use; price and availability are critical to use level.

Dairy Cattle:
Distiller’s grain should be positioned as a protein supplement for dairy. In dairy rations protein quality must be balanced. Distiller’s grains are a good source of methionine. The first limiting amino acid in high producing dairy cows, but low in lysine, a co-limiting amino acid. Five pounds of DDG or ten pounds wet distillers grains is a conservative upper limit. These levels could provide one-half of the supplemental protein with the other half from soybean meal.

Dairy cows consume more feed and the feed passes through the digestive tract more rapidly than in beef cattle. This may increase the bypass value of soybean meal and reduce the difference between DDG and soybean meal. Both DDG and soybean meal are valuable feed ingredients in diets for high producing dairy cows.

Swine:
Pigs require amino acids, not protein. While DDG and DDGS are relatively high in crude protein, the protein is low in lysine, the first limiting amino acid for swine fed grain-based diets. Due to its poor amino acid balance for pigs, amino acid levels become critical in formulating swine rations. If the diets are formulated on crude protein, the diets will be deficient in lysine and other essential amino acids and pig performance will be greatly reduced.

Several studies have been conducted using DDG and DDGS to replace corn in swine rations. The general conclusion is that up to 20 percent of the growing-finishing diets can be DDG or DDGS provided amino acid requirements are met with additions of synthetic amino acids or combined with ingredients that are high in lysine. Therefore, DDG and DDGS must be significantly priced lower than soybean meal to be included in swine rations.

Poultry:
Over the years, there have been several feeding trials with distiller’s grains. As with swine, DDG can be included at levels of 10-20% in broiler and layer feed formulations, provided all essential amino acid requirements are met.

Other considerations:
Care must be given to the quality of the distiller’s by-products. Processing will affect protein quality, amino acid digestibility, and palability. The compositional values in the table are average values that should be replaced when more accurate precise values are obtained.

Storage of DDG and DDGS is critical since they contain about ten percent fat and a large portion of the fatty acids are polyunsaturaturated fatty acids. These fatty acids are unstable and subject to rancidity with time. Therefore, these ingredients should not be stored for long periods of time. Environmental temperatures will determine maximum storage periods.

The nutritionists need to make sure the distiller’s by-products are free of mycotoxins produced by molds in the field or during storage. These mycotoxins can cause reduced performance and reproduction problems in some species.

Summary:
DDG and DDGS are by-products of ethanol production. These feed ingredients should be evaluated on their nutrient composition and price in livestock and poultry rations. The price of these by-products is usually discounted compared to soybean meal. Soybean meal’s advantage is its ability to complement cereal grains in meeting the animals, or bird’s, nutritional requirements for efficient production.

The bottom line comes down to composition, price and availability. If the market demand for ethanol encourages its production, distillers by-products will be produced. These products will be used in feeds, or some other use, at some price.

Table: Comparative composition of corn, distiller's dried grains with solubles and soybean meal.

		Corn	Corn Distiller's	Soybean Meal
			Dried Grains (*)	Solvent	Dehulled
Dry Matter	%	0087.00	0092.00	0090.00	0088.00
Crude Protein	%	0007.90	0027.00	0044.00	0047.80
Ether Extract	%	0003.50	0009.00	0000.50	0001.00
Crude Fiber	%	0001.90	0008.50	0007.00	0003.00
Calcium	%	0000.01	0000.14	0000.25	0000.20
Phosphorus	%	0000.25	0000.89	0000.60	0000.65
Available Phosphorus	%	0000.09	0000.55	0000.20	0000.21
Ash	%	0001.10	0004.50	0006.00	0006.00
Ruminant Digestible Protein	%	0005.80	0021.10	0037.50	0046.60
Ruminant TDN	%	0080.00	0082.00	0078.00	0079.00
Poultry Metabolizable Energy	kcal/lbs.	1540.00	1250.00	1020.00	1125.00
Swine Metabolizable Energy	jcal/lbs.	1520.00	1497.00	1405.00	1425.00
Methionine	%	0000.18	0000.51	0000.65	0000.70
Cystine	%	0000.18	0000.50	0000.67	0000.71
Lysine	%	0000.24	0000.90	0002.90	0003.02
Tryptophan	%	0000.07	0000.20	0000.60	0000.70
Threonine	%	0000.29	0000.92	0001.70	0002.00
Isoleucine	%	0000.29	0001.00	0002.50	0002.60
Hisditine	%	0000.25	0000.65	0001.10	0001.30
Valine	%	0000.42	0001.33	0002.40	0002.70
Leucine	%	0001.00	0002.80	0003.40	0003.80
Arginine	%	0000.40	0001.10	0003.40	0003.60
Phenylalanine	%	0000.42	0001.20	0002.20	0002.70
(*) Corn Distillers Dried Grains with Solubles
Source: Feedstuffs, September 17, 2003

Aines, Glen, Terry Klopfenstein and Rick Stock. 1986. Distillers Grains. Nebraska Cooperative Extension publication MP51.

Davis, Kelly S. 2001. Corn Milling, Processing and Generation of Co-products, Minnesota Nutrition Conference Technical Symposium. September 11.

Dale, Nick and Amy Batal. 2003. Feedstuffs Ingredient Analysis Table: 2003-04 edition. Feedstuffs, September 17.

Thaler, Bob. 2002. Use of Distillers Dried Grains with Solubles (DDGS) in Swine Diets. South Dakota State University Extension Extra publication ExEx 2035.