54 SEPTEMBER 2012 As global consumer demand for fish and shellfish products continues to increase, and the aquaculture industry continues to grow to meet this demand (FAO 2009), demand for traditional feed ingredients in aquafeeds, such as fishmeal, is also increasing (Tacon and Metian 2008). Historically fishmeal has been used as a major component in most aquaculture diets because it has a high protein content, wellbalance profile of highly digestible amino acids, substantial amounts of essential fatty acids, and high digestible energy, vitamin, and mineral content (Abdelghany 2003). However, the decreased availability of fishmeal and increasing cost have caused nutritionists and feed manufacturers to seek less expensive, high quality alternative ingredients, primarily plant-based meals, to partially or completely replace fishmeal in aquafeeds. Unfortunately, replacement of fishmeal with plant-based feed ingredients often results in reduced growth performance (Mbahinzirek et al. 2001, Sklan et al. 2004, Gatlin et al. 2007), unless an adequate amount of other ingredients or dietary supplements are added to meet nutrient requirements, especially amino acids. Therefore, one of the biggest challenges limiting the successful use of alternative plant-based ingredients in aquafeeds is having knowledge of amino acid composition and digestibility. The extensive growth in the U.S. fuel ethanol industry in recent years has led to the production of over 36 million t of distillers grains available for use in animal feeds (Renewable Fuels Association 2011). Maize dried distillers grains with solubles (DDGS), the predominant co-product from the drygrind segment of ethanol manufacture, can be classified as a highly digestible energy and phosphorus, mid-protein ingredient. Other grains (e.g., wheat, sorghum and barley) can also be used or blended with maize to produce DDGS, but maize DDGS is the most common in the USA. During drygrind ethanol production, one bushel (25.4 kg) of maize yields 10.6 L of ethanol and 7.7 kg DDGS (Bothast and Schlicher 2005, Wheals et al. 1999). The American Association of Feed Control Officials (AAFCO 2011) defines DDGS as “the product obtained after the removal of ethyl alcohol by distillation from the yeast fermentation of a grain or a grain mixture by condensing and drying at least ¾ of the solids of the resultant whole stillage and drying it by methods employed in the grain distilling industry. The predominating grain shall be declared as the first word in the name.” The beverage ethanol industry, such as whiskey distilleries, also produces DDGS (< 1 percent of total DDGS production), but it is often dark, tends to be more variable in nutrient content and has lower levels of digestible nutrients than DDGS from fuel ethanol plants. Historically, the majority of wet and dried distillers grains produced in the USA has been fed to cattle, but in recent years, large quantities are being fed to swine and poultry (20 to 30 percent of total production) because of its high nutritional and economic value compared to maize, soybean meal and other competing ingredients. It is an economically attractive feed ingredient because it is often priced at 75 to 80 percent of the value of maize, but contains three times more nutrients than maize. Depending on the animal species, it has an energy value greater than corn for ruminants, equal to corn for swine and about 85 percent the value of corn for poultry. The lower energy value for monogastric species is due primarily to its moderate fiber content. Currently less than 1 percent of the total distillers grains produced are being used in aquafeeds. Therefore, there are tremendous opportunities to use DDGS to a much greater extent as an energy, protein, and digestible phosphorus source. Using DDGS can reduce feed costs and reduce the reliance on fishmeal and other expensive dietary ingredients in aquafeeds. How Does DDGS Compare to Other Maize Co-products? There is often confusion among nutritionists and feed producers regarding the nutritional similarities and differences among maize co-products. Maize DDGS is produced through a dry-grind process that involves grinding and fermenting the entire kernel, whereas wet milling involves separation of the maize kernel into four major products (on a dry matter basis): starch (67.2 percent), gluten feed (19.6 percent), gluten meal containing 60 percent protein (5.7 percent), and germ containing 50 percent corn oil (7.5 percent). Maize gluten feed and meal are feed co-products of the wet milling process. Starch and oil are used for human consumption or biofuels production. In contrast, brewers dried grains are a co-product of beer manufacturing, Maize Dried Distillers Grains with Solubles (DDGS) – A New Alternative Ingredient in Aquafeeds Jerry Shurson 1 FIGURE 1. Maize DDGS is a high-energy, mid-protein, high digestible phosphorus ingredient that offers significant opportunities for use in aquafeeds to reduce feed costs and achieve satisfactory growth performance.
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