The study was conducted at the USDA's meat research center at Clay Center, Nebraska. USDA researcher Jim Wells said his team studied 600 steers. Half the group was fed corn; the other half ate feed that contained 40 percent distiller's grain. The scientists tested the animal's fecal matter.
They were on the lookout for one of the most dangerous forms of the bacteria; E. coli 0157:H7. It can cause a wide range of illness in humans, even death. Wells said the steers fed the distiller's grain ration had more of the harmful E. coli in their digestive tracts. And he attributes that increase to the heavy ration of the ethanol by-product.
"I do believe that for the most part the difference is probably due to diet," said Wells. "But whether or not all of the difference is due to diet we cannot say."
Wells said the study found E. coli in almost 15 percent of the samples from the distiller's grain group. That compares to 1.5 percent in the corn-fed group.
The USDA findings are in line with several other university studies which show a link between distiller's grain and an increased occurrence of E. coli.
Distiller's grain is basically what's left of the corn kernel minus the starch. An ethanol plant converts the starch to sugar and then ferments it.
Wells said it's too early to make any recommendations to cattle producers on whether they should adjust their use of distiller's grain in their cattle feed.
"The point of the study isn't necessarily to say that what someone is doing is bad, it's just to make the people aware that there are consequences," said Wells. "I don't know if I could tell them to change it, because there are advantages to feeding distiller's grain."
One of the most significant advantages is that distiller's grain in most cases is a cheaper form of cattle feed than some of its competitors.
That's important to cattle producers at a time when it's been difficult to make a profit in the business.
It's also important to ethanol companies. They want to sell all the distiller's grain they can, because it helps boost their overall profit.
University of Minnesota associate professor Francisco Diez said the USDA report appears to show conclusively that there is a link between distiller's grain and the prevalence of E. coli.
"Under experimental conditions, yes this effect seems to be real," said Diez. "Seems that it stimulates the number of animals positive for E. coli 0157."
It's not known what role, if any, distiller's grain played in recent E. coli outbreaks. There was a sharp spike in the number of E. coli beef outbreaks in the U.S in 2007, 21 compared to just a half dozen or so the year before.
U.S. Agriculture Department did not return a request for comment. In the past USDA officials have indicated that they do not plan to regulate cattle producer's use of distiller's grain in feed rations. They've said producers themselves can decide that for themselves.