In 2008 I posted, “Grass-Fed vs Grain-Fed Beef and the Holy Grail: A Literature Review,” in which I raised the question if grass-fed beef is safer that grain-fed. My concern was, as I said, that Quotes like these were becoming more common on the Internet and recent media reports:
“Products from grass-fed animals are safer than food from conventionally-raised animals.” Eatwild, 2008
“Research has shown that the strains of E. coli most devastating to humans are the product of feedlots, not cows. This is due to the animals being forced to eat an unnatural diet, and not their natural choice, grass.” Grass-Fed Beef: Safer and Healthier, Animal Welfare Approved, June 15, 2008
My conclusion of the literature review was: In summary, the scientific evidence at this time does not support a broad conclusion that grass feeding significantly reduces the risk of E. coli O157:H7 or other dangerous foodborne pathogens from entering the food chain. However, more research is needed to better understand the influence of diet, especially the use of different types of grains in animal feed.
Now a recent abstract entitled, “Contamination Rates and Antimicrobial Resistance in Bacteria Isolated from “Grass-Fed” Labeled Beef Products” by Jiayi Zhang, Samantha K. Wall, Li Xu, Paul D. Ebner in Foodborne Pathogens and Disease, once again puts into question the conventional wisdom that somehow grass-fed cows are safer than grain-fed cows. Here is the abstract in part:
Abstract: Grass-fed and organic beef products make up a growing share of the beef market in the United States. While processing, animal handling, and farm management play large roles in determining the safety of final beef products, grass-fed beef products are often marketed as safer alternatives to grain-finished beef products based on the potential effects of all-forage diets on host microbiota.
We conducted a series of experiments examining bacterial contamination rates in 50 beef products labeled as “grass-fed” versus 50 conventionally raised retail beef products.
Coliform concentrations did not differ between conventional and grass-fed beef (conventional: 2.6 log10 CFU/mL rinsate; grass-fed: 2.7 log10 CFU/mL rinsate). The percentages of Escherichia coli positive samples did not differ between the two groups (44% vs. 44%). Enterococcus spp., were frequently isolated from both grass-fed beef products (44%) and conventional beef products (62%; p = 0.07). No Salmonella or E. coli O157:H7 isolates were recovered from any of the meat samples. Enterococcus spp. isolates from conventional beef were more frequently resistant to daptomycin and linezolid (p < 0.05). Resistance to some antimicrobials (e.g., chloramphenicol, erythromycin, flavomycin, penicillin, and tetracyline) was high in Enterococcus spp. isolated from both conventional and grass-fed beef.
There were no differences in the percentages of antimicrobial resistant E. coli isolates between the two groups. Taken together, these data indicate that there are no clear food safety advantages to grass-fed beef products over conventional beef products.
Perhaps more research is still needed. The sample size of this recent study was small. Perhaps Food Safety News should do a larger one?