Safety of biofuel coproducts, such as distillers grains from corn-grain ethanol production, as animal feedstuffs can pose a barrier to meeting the Renewable Fuel Standard (RFS2) because whether those biofuel products meet the GHG reduction threshold of RFS depends in part on GHG credits from coproducts. The safety concerns include health and welfare of the animals consuming the coproducts and the safety of the foods that are derived from these animals. Both of these issues are affected by the presence of antibiotic residues and mycotoxins in distillers grains and the potential increase in fecal shedding of Escherichia coli O157 in cattle that were given distillers grains as part of their ration.
In corn-grain or sugar-based ethanol production, bacterial contamination during the fermentation is a concern (Skinner and Leathers, 2004). Bacterial contaminants compete with the ethanol-producing yeast for sugars and micronutrients, and they produce organic acids that inhibit yeast, thereby reducing ethanol yield. Antibiotics, including virginiamycin, erythromycin, and tylosin, are sometimes added to control or prevent bacterial contamination in biorefineries. Administering these antibiotics to animals is strictly regulated by the Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA), especially immediately prior to slaughter or to egg-laying hens and lactating cattle. When coproducts containing antibiotics are inadvertently fed to livestock, residues in meat, milk, or eggs could result in condemnation of products or, if not discovered, unacceptably high levels in human foods. FDA is concerned about the potential animal and human health hazards from antibiotic residues in distillers grains used as animal feed. In 2009, FDA announced that it would conduct a nationwide survey to determine the extent and levels of antibiotic residues in distillers grains produced in the United States (FDA, 2009). The outcome of the survey could resolve whether antibiotic residue in corn-grain ethanol coproducts would be a barrier to achieving RFS2. Alternative to antibiotics such as stabilized chlorine dioxide also can be used to control or prevent bacterial contamination.
Corn grain might be contaminated by mycotoxins (toxins produced by fungi). These mycotoxins are typically concentrated by about two to three fold when the corn grain is converted to distillers grains because starch comprises about two-thirds of the grain and
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.
Corzo, A., M.W. Schilling, R.E. Loar, V. Jackson, S. Kin, and V. Radhakrishnan. 2009. The effects of feeding distillers dried grains with solubles on broiler meat quality. Poultry Science 88(2):432-439.
Depenbusch, B.E., C.M. Coleman, J.J. Higgins, and J.S. Drouillard. 2009. Effects of increasing levels of dried corn distillers grains with solubles on growth performance, carcass characteristics, and meat quality of yearling heifers. Journal of Animal Science 87(8):2653-2663.
Edrington, T.S., J.C. MacDonald, R.L. Farrow, T.R. Callaway, R.C. Anderson, and D.J. Nisbet. 2010. Influence of wet distiller’s grains on prevalence of Escherichia coli O157:H7 and salmonella in feedlot cattle and antimicrobial susceptibility of generic Escherichia coli isolates. Foodborne Pathogens and Disease 7(5):605-608.
FDA (Food and Drug Adminstration). 2009. FY 2010 Nationwide Survey of Distillers Grains for Antibiotic Residues. Available online at http://www.fda.gov/AnimalVeterinary/Products/AnimalFoodFeeds/Contaminants/ucm190907.htm. Accessed September 6, 2010.
Jacob, M.E., J.T. Fox, J.S. Drouillard, D.G. Renter, and T.G. Nagaraja. 2008a. Effects of dried distillers’ grain on fecal prevalence and growth of Escherichia coli O157 in batch culture fermentations from cattle. Applied and Environmental Microbiology 74(1):38-43.
Jacob, M.E., J.T. Fox, S.K. Narayanan, J.S. Drouillard, D.G. Renter, and T.G. Nagaraja. 2008b. Effects of feeding wet corn distillers grains with solubles with or without monensin and tylosin on the prevalence and antimicrobial susceptibilities of fecal foodborne pathogenic and commensal bacteria in feedlot cattle. Journal of Animal Science 86(5):1182-1190.
Leytem, A.B., P. Kwanyuen, and P. Thacker. 2008. Nutrient excretion, phosphorus characterization, and phosphorus solubility in excreta from broiler chicks fed diets containing graded levels of wheat distillers grains with solubles. Poultry Science 87(12):2505-2511.
Schmit, T.M., R.N. Boisvert, D. Enahoro, and L.E. Chase. 2009. Optimal dairy farm adjustments to increased utilization of corn distillers dried grains with solubles. Journal of Dairy Science 92(12):6105-6115.
Seigel, V. 2010. Corn dried distillers grains and mycotoxins. Paper presented at the 14th Distillers Grains Symposium, May 12-13, Indianapolis, IN.
Skinner, K.A., and T.D. Leathers. 2004. Bacterial contaminants of fuel ethanol production. Journal of Industrial Microbiology & Biotechnology 31(9):401-408.
Whitlow, L. 2008. Mycotoxins cause concerns. Available online at http://ethanolproducer.com/dgq/article.jsp?article_id=1233&article_title=Mycotoxins+cause+concerns. Accessed September 7, 2010.
Wild, C.P., and Y.Y. Gong. 2010. Mycotoxins and human disease: A largely ignored global health issue. Carcinogenesis 31(1):71-82.
Xu, G., S.K. Baidoo, L.J. Johnston, J.E. Cannon, and G.C. Shurson. 2007. Effects of adding increasing levels of corn dried distillers grains with solubles (DDGS) to corn-soybean meal diets on growth performance and pork quality of growing-finishing pigs. Journal of Animal Science 85:76.
Xu, G., S.K. Baidoo, L.J. Johnston, D. Bibus, J.E. Cannon, and G.C. Shurson. 2010. Effects of feeding diets containing increasing content of corn distillers dried grains with solubles to grower-finisher pigs on growth performance, carcass composition, and pork fat quality. Journal of Animal Science 88(4):1398-1410.
Zhang, Y.H., J. Caupert, P.M. Imerman, J.L. Richard, and G.C. Shurson. 2009. The occurrence and concentration of mycotoxins in US distillers dried grains with solubles. Journal of Agricultural and Food Chemistry 57(20):9828-9837.
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