Cowgirl? They named her right.
Corn fed, especially if they are dry lotted about 30 days before "the knife" will result in more inter and intra muscular marbling.....aka, fat. White fat. That means a tender, juicy, flavorful piece of meat. The difference between good, choice and prime is tied to the degree of marbling. That comes from how its fed, but also the age and genetics of the animal eating it. Certain beef breeds do better than others. Dairy breeds don't put on much fat.
Grass fed is portrayed as being more healthy, as the fat content is lower. So take out the tender, juicy and flavorful and it's basically the same. It's also cheaper to produce, as they are eating grass vs. grain, which right now is sky high expensive relative to where its been for the last 100 years.