For what it's worth, even grass fed animals eat some grain. Wild grasses and herbs go to seed at different times of the year, and when cows (or deer, or bison, etc.) graze they eat the whole thing, leaves, stems and seeds. When we make a grass-fed versus grain-fed distinction, we're plotting a point in a gray area between these two extremes. Unless you buy factory farmed meat, which might be entirely grain fed.