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O
Safety and Quality of Biofuel
Coproducts as Animal Feed
S
afety of biofuel coproducts, such as distillers grains from corn-grain ethanol produc-
tion, 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 virginia-
mycin, erythromycin, and tylosin, are sometimes added to control or prevent bacterial
contamination in biorefineries. Administering these antibiotics to animals is strictly regu-
lated 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, un-
acceptably 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
391
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392 APPENDIX O
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 deoxyniva-
lenol 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 contri-
bution 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 re-
ported 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.
REFERENCES
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in composition of DDGS. Animal Feed Science and Technology 159(3-4):122-130.
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393
APPENDIX O
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