Grass-fed beef comes from cattle that eat only grass and other foraged foods. Usually, beef and dairy cows eat a diet of processed grain, such as corn. There has been an increased interest in grass-fed or pastured beef because of its health claims when compared to cattle from commercial feedlots. Grass-fed beef may have some heart-health benefits that other types of beef don’t have. When compared with other types of beef, grass-fed beef may have:
- Less total fat
- Higher levels of heart-healthy omega-3 fatty acids
- Higher levels of another type of fat (conjugated linoleic acid) that’s thought to reduce heart disease and cancer risks
- Lower levels of a dangerous strain of E. coli bacteria
Due to the almost continuous news of recalls of beef contaminated with a dangerous strain of E. coli 0157:H7 or often just called O157 bacteria, grass-fed beef purveyors have often promoted the idea of safer beef than conventionally-grown or grain-fed beef. What does the science say?
Work conducted at Cornell University by Russell and Diez-Gonzalez in the late 1990s showed that cattle that were fed hay had far fewer E. coli concentrations than when they were fed a standard feedlot diet based on grain. (Microbes Infect 2, No. 1 (2000): 45-53.) However, earlier studies did not look at the levels of the dangerous strain 0157 apart from other strains.
The researchers hypothesized that when grain is fed to cattle, their digestive tracts become more acidic. Over time, the E. coli in their intestines become resistant to this acid environment. When we ingest them, a high percentage will survive the high acid content of our digestive juices and increase the risk of E. coli food poisoning. Theoretically few E. coli from grass-fed cattle will survive because they have not become acid-resistant.
Since this original work, other researchers have explored the link between cattle feed and E. coli with more attention paid to the presence of 0157:H7. Some have confirmed the work by Russell and Diez-Gonzalez but the majority has disputed the finding. For example, in 2003, at the University of Idaho, a study found no difference in the levels of E. coli 0157:H7 in grass-fed and grain-fed. In both cases, acid resistance was high. Other studies have come to the same conclusion.
Grass-fed growers point out that even if there is not much evidence that diet can affect the number and acidity of E. coli in the intestines of cattle, grass-fed beef may be safer in the long run than feedlot beef. Simply, grass-fed cattle are cleaner at time of slaughter.
Feedlot animals often stand all day in dirt and manure and careless and dangerous practices in the slaughterhouses increases the risk of manure contamination of the meat. For a graphic depiction of slaughterhouse practices, read “Fast Food Nation” by Eric Schlosser. A cleaner animal upon entering the facility will lessen this possibility. In the magazine Meat Marketing and Technology, the associate editor stated: “pasture-raised animals are much easier to clean because they come form smaller herds raised in relatively cleaner pastures.”
From the www.onlygrassfed.com webpage:
“It (grass-fed) is usually processed in a small local meat processing operation by skilled butchers who are careful to avoid fecal contamination of the beef. When you buy grass fed ground beef from a reputable local farmer, you can be assured it is not “frankenbeef.” In fact, the ground beef probably came from one cow. Rest assured, it was processed from quality, uncontaminated ingredients.”
In 2009, there were 4,643 cases of Shiga-toxin producing 0157:H7 E. coli illnesses; In 2010, the number rose to 4, 757. Fortunately there were few deaths, but this strain can cause a condition known as hemolytic uremic syndrome (HUS) often with lasting kidney damage for a lifetime.
Choosing whether to buy grass-fed or grain-fed beef is a personal decision based on taste, price, ethical and environmental issues. Some grass-fed beef purveyors will say that it is OK to consume the beef raw as in steak tartar, for example based on the myth of less E. coli contamination. If you choose grass-fed beef it is important to realize that you should practice all the safe-handling techniques recommended for grain-fed beef based on the current scientific evidence.
FOOD, FACTS and FADS 
