According to a recent study done by investigators from Purdue University in Indiana and Zhejiang University in Hangzhou, China, there is no safety advantage to consuming grass-fed beef over conventionally raised beef. 

Researchers investigated a modest sample of U.S. retail beef products and found that marketing which claims that grass-fed beef is safer than conventionally raised beef is not necessarily true.  

The study was released in the magazine Foodborne Pathogens and Disease in July.

Reviewed by professors at the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, researchers found that there were no significant differences in the presence of total coliform bacteria, Escherichia coli, or Enterococcus species between grass-fed and conventionally fed beef.

Alternatively, researchers found evidence that indicates conventional beef has an increased resistance to bacteria when compared with grass-fed beef.

“Taken together, these data indicate that there are no clear food safety advantages to grass-fed beef products over conventional beef products,” says the report by investigators from Purdue University in Indiana and Zhejiang University in Hangzhou, China.

According to the authors, though results of the study show no clear advantages to grass-fed cattle over conventionally raised cattle, other factors play a large roll in affecting the safety of the meat.  These factors include how the beef is processed, whether cattle are fed preventative antimicrobials, and other factors.  The authors explain that grass-fed cattle are more likely to be processed in small facilities and are less likely to be given preventative antibiotics.  

Testing showed no difference in overall coliform contamination of the sample sets. Likewise, solid cuts and ground beef did not differ in coliform levels.

Enterooccus species were isolated from 62 percent of the conventional samples and 44 percent of the grass-fed samples, a difference that did not reach significance.  However, the difference was greater for ground beef: 75 percent for conventional versus 41 percent for grass-fed.

The two sample sets had equal overall levels of E. coli contamination, at 44 percent. For solid cuts of meat, the conventional products had a higher level of E. coli than the grass-fed products, but this was reversed for ground beef.  Neither difference was significant.  No E. coli O157:H7 or Salmonella was found in any of the samples.

Additionally, the investigators found no differences in the percentages of resistant E. coli from conventional versus grass-fed beef.  However, Enterococcus species from conventional beef were more frequently resistant to daptomycin and linezolid than were the same species from grass-fed beef, they report.  They also found that both E. coli and Enterococcus from conventional beef showed higher resistance to several antibiotics than the same species from grass-fed beef, in terms of the amount of drug needed to inhibit the organism.

Though researchers found few significant differences between grass-fed and conventional beef,  they concluded that there was an “overall trend” for more Enterococcus species found in conventional beef while more E. coli was found in grass-fed beef.  Findings on resistance indicate, “a possible trend for bacteria isolated from conventional products to be more antimicrobial-resistant.”

Director of education at the University of Minnesota Center for Animal Health and Food Safety Scott J. Wells said study results were intriguing, but the small sample size limits the applicability conclusions.

“The low sample size limits inference generally as well as limits authors from further evaluating differences between specific subtypes of retail beef products,” he wrote.  Wells also added that the low prevalence of E. coli O157 and Salmonella in the beef supply means that a much larger sample would be needed to compare levels in grass-fed versus conventional beef.

Wells also wrote that “Contamination of retail beef samples by certain bacterial pathogens is a complex process, with multiple points of potential contamination . . . and several risk factors that could potentially mitigate the outcome. It’s not likely to be as simple as grass-fed vs conventional fed.”

In addition, Wells observed that other factors including farm size and type of farm management system can contribute to the level of bacteria in beef. “In short, the article is interesting but I’m left with more questions,” he said.

The study abstract is available online.