Researchers say there's no definitive link between distillers grains diets in cattle and higher rates of E. coli O157:H7 shedding.
There's probably some association between the use of distillers grains (DGs) in cattle diets and the increased presence of E. coli O157:H7 but further testing is needed to determine exactly the relationship. That's the conclusion of three researchers who have studied E. coli O157:H7 for a number of years.
Guy Loneragan, West Texas A&M University epidemiologist, says he doesn't believe use of DGs definitely or consistently increases the presence of E. coli O157:H7, but does believe there's a relationship between the feed and increased presence of the bacteria.
“In the mid 1990s, Cornell researchers said a diet change in cattle from grain feeding to roughage, or substituting fiber for starch, would reduce the presence of E. coli O157:H7. But research shows increased E. coli O157:H7 shedding,” he says.
“We know there's an unusual relationship but can't say for certain that use of DGs definitely increases E. coli shedding. A better understanding of all the circumstances that increase shedding of E. coli O157:H7 is needed.”
The controversy began late in 2007 when Kansas State University (KSU) researchers found higher levels of the bacteria in the feces of cattle consuming DGs. The news coincided with a 21-million-lb. beef recall by Topps Meat of Elizabeth, NJ, due to E. coli O157:H7 contamination of ground beef.
Loneragan notes that the 2007 contamination spike doesn't necessarily mean feeding ethanol byproducts precipitated the increase.
“To determine the source of the increased bacteria, you have to consider the dominant drivers of E. coli shedding,” he says. “The biggest driver, regardless of diet, is the season. From May through October, E. coli shedding increases. If there's a relationship between use of DGs and increased presence of E. coli O157:H7, I suspect it's a marginal problem.”
T.G. Nagaraja, KSU microbiology professor, agrees more study is needed. “We made our initial observation in 2005 in cattle fed DGs,” he says. “We found a higher rate of E. coli shedding in their feces, which prompted us to design three further studies. We've now completed two of those.”
Findings in the first study indicated a significantly higher level of E. coli shed in cattle fed DGs, he says. But the second study showed a slight increase in shedding rate, though not enough to be significant.
So what type of diet causes increased shedding? Some researchers claim grain feeding increases shedding; others say forage. But neither eliminates the problem of E. coli O157:H7 because the bacteria is naturally present in the gut of cattle.
Beyond vaccination and working to keep the bacteria out of water and feed supplies, researchers say producers have few options in reducing E. coli O157:H7 shedding in cattle. In fact, scraping pens has actually proven to increase bacteria because it exposes the bacteria thriving underneath the manure.
David Smith, University of Nebraska-Lincoln (UNL) Extension veterinarian, says UNL testing of a Canadian vaccine found vaccinated cattle were 98% less likely to be colonized with E. coli O157:H7 at slaughter. The vaccine is approved and in use in Canada, but not in the U.S.
“That same study also showed cattle fed 30% dry matter (DM) or less were less likely to shed E. coli,” he says. “So they appeared to be protected from shedding E. coli O157:H7 by eating DGs. Those fed 40% DM or more shed more of the bacteria.”
But if there's a relationship, it's a complicated one, Smith adds. “It isn't just a matter of adding more DGs and seeing more shedding. There's something going on at some level that's resulting in either a degree of protection or increased risk.”
Thus, he cautions against jumping to conclusions. “We must guard against making policy decisions before we reach a clear understanding of the relationship between DGs and shedding of E. coli O157:H7,” he says.
Loretta Sorensen is a freelance writer based in Yankton, SD.