Does Ethanol Raise Risks?
Tuesday, November 4, 2008
Last year scientists noted an uptick in the prevalence of potentially deadly E. coli O157:H7 bacteria in beef products. Frequently found in the digestive tracts of cattle, the bug can wind up in ground beef during the slaughter and grinding process.
There were 21 beef recalls in the United States in 2007, compared with eight the year before. About a third of the recalls were prompted by reports of human illness, while none of the 2006 recalls were.
This year, meat inspectors from the U.S. Department of Agriculture have continued to see more contaminated beef samples. Through mid-October, they had recorded 50 percent more than at the same time last year.
Officials have assumed that these numbers reflect an overall increase in the prevalence of the E. coli strain in cattle, but no one has been able to explain why the dangerous bacteria have become more abundant.
Now scientists are looking into a possible explanation -- one that's related to alternative fuels and the economics of farming.
It started with a study that came out in late 2007, while consumers were still digesting news of the recall of 21 million pounds of ground beef by Topps Meat of Elizabeth, N.J.
Researchers at Kansas State University who were studying the types of bacteria that live in cattle feces unexpectedly found higher levels of E. coli O157:H7 in the feces of cattle fed a diet that included an ethanol product called distillers grain.
Distillers grain is what is left after the starch from corn is removed to make ethanol. It has been around for decades, but its popularity as a feed ingredient has surged in recent years. One reason is that demand for ethanol, fueled by rising gas prices and federal mandates and subsidies, has pushed the price of corn -- and in turn, corn feed -- to record levels, said Darrell Mark, an economist at the University of Nebraska at Lincoln.
Distillers grain is also cheaper than corn and is high in the proteins and fats that help cattle put on more weight, said David M. Smith, a University of Nebraska researcher. For cattle ranchers, who are being squeezed by lower beef consumption and higher prices for fuel and grazing land, such benefits are important.
The researchers at Kansas State followed up with another study in which they inoculated calves with E. coli O157:H7 (which is harmless to cattle) using a modified form of the bacteria that was easier to track. They found that calves fed distillers grain had higher levels of the bacteria than those that were not. The USDA findings appear to back them up.
But the connection between distillers grain and E. coli is still far from conclusive, researchers said, for several reasons. Another study done by researchers at the University of Nebraska found that cattle fed a diet of up to 25 percent distillers grain actually had less of the bacteria than the control group, while those fed a diet that was 40 percent or more distillers grain had more of the bacteria. Another study done at Kansas State found no statistically significant increase in the bacteria in distillers-grain-fed cattle compared with the control.
T.G. Nagaraja, one of the Kansas State researchers, suggests that the variation in results may be due to differences in the distillers grain, which can depend on where it was produced.
Nagaraja believes there is some link between distillers grain and E. coli levels, but he isn't ready to say it contributed to the wave of recalls in 2007.
"We don't have any evidence to support that because we haven't gone to the slaughterhouse to see whether there could be a link between higher beef contamination and more positive cattle," he said.
Researchers have reason to be cautious, Smith said, because mistakes have been made before. For example, it was once thought that the organism was rare in cattle. "In truth, almost all cattle are exposed to and shed the agent at some point in their lives," Smith said. People also used to believe that cleaning cattle water tanks would control transmission. It doesn't.
Guy Loneragan, a food safety expert at West Texas A&M University, who has studied different ways of keeping E. coli out of the beef production process, said it is hard to draw firm conclusions from the studies that have been done because there is still a lot that scientists don't understand about the bacteria. Its prevalence is highly unstable, he said, and can vary day to day, pen to pen. So far, seasonality is the strongest predictor of E. coli levels: They tend to be higher in the summer. The bacteria have not responded consistently to changes in diet, at least not in the studies done so far.
"If we look at one study or one piece of one study, the effect looks bigger than it is," he said. "If you look at studies together, there may be an effect but probably not as great as what we're concerned about."