its removal by fermentation results in the enrichment of mycotoxins in the distillers grains (Whitlow, 2008). Mycotoxins of particular concerns are aflatoxins and fumonisin. Aflatoxin is carcinogenic and affects the liver (Wild and Gong, 2010). Fumonisins have been reported to induce liver and kidney tumors in rodents and identified as possibly carcinogenic to humans. Both mycotoxins affect growth and are immunosuppressive in animals (Wild and Gong, 2010).
One study assessed aflatoxins, deoxynivalenol, fumonisins, T-2 toxin, and zearalenone in samples of distillers grains from 20 ethanol refineries in the Midwestern United States (Zhang et al., 2009). That study found that none of the samples had aflatoxins or deoxynivalenol levels that exceed FDA guidelines for use as animal feed and that less than 10 percent of the samples had fumonisin levels that exceed FDA guideline for feeding equids and rabbits. However, the level of mycotoxins in corn depends on the weather and the amount of insect damage sustained by the plants and therefore is likely to vary from year to year. In a survey of dried distillers grain (DDG) samples from 2009-2010 corn crops in Indiana, Siegel (2010) found that 20 percent of the DDG had mycotoxin levels that were too high to be used as animal feed. These contaminated DDG were mostly disposed of by applying to land as fertilizer.
Another concern of using distillers grains as part of animal feed is its potential contribution to increased prevalence of Escherichia coli O157 in cattle. Prevalence of E. coli O157 in cattle could be a food safety concern. Jacob et al. (2008a,b) compared the prevalence of E. coli 157 in feces of cattle that were fed diets with wet or dried distillers grains to those without distillers grains at all. They found an increase in E.coli O157 prevalence in batch cultures of ruminal and fecal fermentation of cattle fed DDG (Jacob et al., 2008a). However, the effect of feeding wet distillers grains on E. coli O157 prevalence in cattle was inconclusive (Jacob et al., 2008b). Edrington et al. (2010) also did not observe any effect of feeding wet distillers grains on E. coli O157 in feedlot cattle.
In addition to food safety, the nutritional quality of DDG could be a concern if they are to be included in animal diets. Variations in DDG composition affect nutritional quality and market value. Samples of DDG from dry grind ethanol biorefineries in the upper Midwest were found to have consistent fat content but variable protein content that ranged from 260 to 380 g/kg of dry matter (Belyea et al., 2010). In general, including DDG in animal diets does not appear to affect meat and carcass quality of broilers, pigs, and heifers (Xu et al., 2007, 2010; Corzo et al., 2009; Depenbusch et al., 2009). However, finishing pigs fed with a diet of over 20 percent DDG could have fat quality that does not meet the standard of pork processors (Xu et al., 2010). High levels of fat in DDG cause milk fat depression in dairy cattle and limit the inclusion rates in dairy feeds. New technologies that remove the fat from DDG promise to circumvent this problem. This high variability in protein content and quality diminishes the value of DDG as a feedstuff, especially for poultry and pigs.
Use of a large proportion of DDG in animal diet also raises environmental concerns. Inclusion of DDG in poultry diets was shown to increase nitrogen and phosphorus levels in poultry excreta. Moreover, the solubility of excreted phosphorus in poultry fed with DDG is higher than that of poultry without DDG in its diet (Leytem et al., 2008). Another study reported high phosphorus excretion in dry cows and heifers that were fed with DDG (Schmit et al., 2009). Disposal of the manure with high nutrient content is an environmental concern.
Belyea, R.L., K.D. Rausch, T.E. Clevenger, V. Singh, D.B. Johnston, and M.E. Tumbleson. 2010. Sources of variation in composition of DDGS. Animal Feed Science and Technology 159(3-4):122-130.