WORLD AQUACULTURE 55 consisting of the dried residue of barley malt and other grains that have been used to provide maltose and dextrins for fermentation. Use of brewers dried grains in monogastric animal diets is limited because it has a relatively high fiber level (18 to 19 percent). As a result of the different grains and processes used to produce co-products, they are nutritionally different. The primary nutritional advantages of DDGS are its high oil and digestible phosphorus content compared to corn gluten feed, corn gluten meal and brewers dried grains. The digestible energy content of DDGS is much higher than corn gluten feed and brewers dried grains, comparable to corn, but less than corn gluten meal for monogastric species. Amino acid levels of DDGS are lower than in corn gluten meal and corn germ meal, and are comparable to corn gluten feed and brewers dried grains, but can vary in their digestibility based on the extent of heating used during drying. Nutritional Value of DDGS in Aquafeeds Maize DDGS is a high energy, mid-protein, highly digestible phosphorus ingredient. However, nutrient content and digestibility varies among sources (Spiehs et al. 2002). Most energy in DDGS is derived from a relatively high crude fat content, with lesser amounts contributed by residual starch, fiber and protein. The crude fat content of DDGS is approximately 10 percent (as fed-basis) and the total fat is comprised of linoleic acid (55.7 percent), linolenic acid (7.8 percent) and DHA (0.14 percent). As a result, DDGS has a high omega-6 to omega-3 ratio. During the past two years, over 50 percent of the 207 ethanol plants in the USA are now extracting some of the oil before making DDGS because marketing crude corn oil is highly profitable. Therefore, the crude fat content of DDGS has become more variable (5 to 12 percent) and reduced-oil DDGS will result in less digestible energy. The starch content of DDGS is low, ranging from 1.1 to 7.9 percent (on a dry matter basis), depending on the extent of starch fermentation to ethanol (Anderson et al. 2012). It is not known if starch in DDGS is digestible or in the form of resistant starch. DDGS has crude fiber (6.6 percent), ADF (11.1 percent), NDF (37.6 percent) and TDF (31.8 percent) and the majority (96.5 percent) of TDF is insoluble fiber (Urriola et al. 2010). Neutral detergent fiber content is one of the most variable nutritional components in DDGS and it is unclear whether this is because of high variability in analytical measurement among laboratories or if fiber content is truly this variable among DDGS sources. Fiber digestibility of DDGS has not been determined in fish, but studies conducted with other monogastric species indicate that fiber digestibility can be significant, but variable. Fish with greater ability to utilize high fiber diets perform well at high dietary DDGS inclusion rates compared with other species with very little lower gut fermentation. Despite the relatively high crude protein content of DDGS (27 percent), lysine, methionine, threonine, and tryptophan concentrations are relatively low in relation to the amino acid requirements of fish. Furthermore, lysine is the most variable of all amino acids among DDGS sources and its digestibility depends on the extent of heating during DDGS production. As a result, fish diets requiring high protein levels must be supplemented with crystalline amino acids when large amounts of DDGS are added. Apparent digestibility of amino acids in DDGS have been determined in rainbow trout diets and are relatively high (> 90 percent for all essential amino acids except threonine) but amino acid digestibility has not been determined for other fish species (Cheng and Hardy 2004a). The phosphorus content in DDGS (0.75 percent) is greater than other plant-based ingredients and much of the phytate phosphorus is released during corn fermentation in ethanol production, making it highly digestible for monogastric species (Stein and Shurson 2009). However, DDGS phosphorus digestibility and availability have not been determined in fish. Concentration of vitamins, including riboflavin, niacin, pantothenic acid, folic acid and choline, are about three times greater in DDGS than in corn (Hertrampf and Piedad-Pascual 2000). Macrominerals, such as calcium, chlorine and potassium, are in low concentration in DDGS relative to fish requirements and must be supplemented (Hertrampf and Piedad-Pascual 2000). Furthermore, zinc, iron, manganese and copper concentrations in DDGS are lower than in typical fishmeal, but requirements can easily be met with diet supplementation of these micronutrients. Limited data are available for the xanthophyll content and bioavailability in DDGS, or its impact on flesh color in fish, but the few values reported in the literature indicate that it can vary from 3.5 to 29.8 mg/kg. One of the distinct advantages of DDGS compared to other plant-based ingredients is that it does not contain antinutritional factors, such as those found in soybean meal (trypsin inhibitors; Wilson and Poe 1985, Shiau et al. 1987), rapeseed meal (glucosinolates and erucic acid) and cottonseed meal (gossypol; Jauncey and Ross 1982, Robinson 1991). DDGS contains low levels of phytate compared with other plant-derived feed ingredients. A Summary of Research Results Using DDGS in Aquafeeds • Channel Catfish Ictalurus punctatus Multiple studies (Tidwell 1990; Webster et al. 1993; Robinson and Lee 2008; Zhou et al. 2010) determined that relatively high (30 percent) dietary inclusion rates of DDGS can 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. (CONTINUED ON PAGE 56)
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