Research spanning three decades suggests that grass-based diets can significantly improve the fatty acid (FA) composition and antioxidant content of beef, albeit with variable impacts on overall palatability. Grass-based diets have been shown to enhance total conjugated linoleic acid (CLA) (C18:2) isomers, trans vaccenic acid (TVA) (C18:1 t11), a precursor to CLA, and omega-3 (n-3) FAs on a g/g fat basis.
This is an interesting study, but it does indicate that in many studies the cattle are not really grass-fed and the grain-fed cattle are only partially so. That's because the researches don't know enough about the livestock business to ask the right questions. Also, some variations occur from the analytical methods used and what parts of the animal were analyzed. The differences between eating grass and being fed hay are also a question, but the grains have relatively uniform differences in EFA profiles. So if a steer is fed 160 days an 80% grain ratio (the standard mix and the grain portion is usually corn) then it's EFA ratio should be up around 15 : 1. In a feedlot steers gain about 3.2 pounds per day. So in 160 days they gain 512 pounds which is about a 68% increase in body mass.
In one ounce of corn there is: Total Omega-3 fatty acids 18.2 mg and Total Omega-6 fatty acids of 587 mg.
At the average weight in the feedlot (1000 pounds) the steer will eat 2.6% of body weight or 26 pounds of feed with 20.87 pounds of it being corn. With that kind of intake, and with the knowledge that the O6 overloads block the absorption of O3, one has to imagine significant change in the O6 direction, more than the studies suggest.
Only one study indicated a 1.44 to one ratio for grass-fed and it's grain-fed ratio was 3 : 1. To me, that means that particular study was flawed from the onset. So this review is a good example of one that contains flaws and why there remains naysayers regarding the benefits of grass-fed meats.