The dry-milling industry ferments the starch in grain (corn, sorghum, barley) to ethanol. The dry grain is ground, mixed with water, and cooked, and then an enzyme is added to convert the starch to glucose. The glucose is fermented to ethanol using added yeast. When the alcohol is removed, the resulting stillage is high in moisture and usually separated into wet grains and thin stillage by screening or centrifuging. In the past, these byproducts were dried in drum dryers to produce dried distiller's grains (DDG) or dried distillers grains with solubles (DDGS). The solubles are commonly used in beef-cattle feedlots as either a dietary ingredient or a carrier for liquid supplements.
In the early 1980s, researchers started evaluating the feeding of distillers grains and/or solubles wet. Klopfenstein and Grant summarized 11 experiments in which wet distillers by-products were fed in beef cattle finishing diets. At 17.4% of the diet dry matter, this byproduct had 150% the feeding value of corn, and when fed at 40% of the diet, 136% the value of corn. The protein in distillers grains is about 30% and the fat is about 12%. Typically, DDG (or DDGS) are used as a protein supplement in ruminant diets. Feed manufacturers use DDG in beef and dairy supplements and feeds. Many larger dairies use DDG as a commodity feed ingredient for use in total mixed rations. Initially, beef-cattle feedlots were reluctant to use wet distillers products as an energy source in beef-cattle finishing diets. However, the practice of feeding wet distillers by-products within 100 to 150 miles of an ethanol plant is becoming common.
DDG and DDGS are excellent sources of rumen-undegraded protein. This is an advantage for ruminants such as lactating beef or dairy cows that have high protein requirements. The relatively high fat content ensures a high energy content diet. The corn fiber (hull) in forage-based diets is highly digested by cattle. The high protein and bypass, high fat, and fiber contents of DDG are especially useful in lactating dairy diets.
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