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Grass, Grain, Beef and E. coli

Most beef cattle in the United States consume a diet containing grain during the last part of their lives. American consumers can also purchase grass-fed beef from cattle that consume only grass or forage for their entire lives. Are there any differences between these two products when it comes to food safety?

E. coli O157:H7 is a bacterium that is associated with cattle.  A few popular books have made the claim that E. coli O157:H7 outbreaks are the result of modern beef production practices where cattle are fed diets containing higher amounts of corn or other starches (as opposed to grass or other forage). 

The roots of these claims are traced back to a few studies that showed that feeding higher amounts of grain to cattle can lower the pH (more acidic) of the cow’s intestinal tract.  This could then favor the growth of acid-tolerant bacteria like some E. coli.  While not the conclusion of the study, some folks have interpreted this to mean that feeding grain over grass has resulted in the emergence of E. coli O157:H7. 

Studies looking at actual E. coli O157:H7 carriage rates in cattle fed high starch (e.g., corn) vs. high forage (e.g., grass), however, have been inconsistent.  Some studies have shown that E. coli O157:H7 carriage rates are not related to pH levels and others have shown that E. coli O157:H7 carriage rates can actually be higher in cattle fed high levels of grass.  Taken together, the studies to date have not shown that grain-fed cattle more frequently carry E. coli O157:H7.

There are differences between grass-fed and grain-fed beef products.  Grass-fed beef is generally leaner, but with higher concentrations of healthy fats. There can also be differences in taste.  In terms of safety, however, grass-fed beef has no clear benefit over grain-fed beef. 

Paul Ebner, PhD
Assistant Professor
Dept. of Animal Sciences

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