I think it's important to point out though that cattle can digest and "convert" a significantly wider variety of plant sources into meat. Our bodies simply can't digest a lot of what they can.
Sure... but it's also important to point out that while cattle "should" eat grass and can eat silage... 78% of beef in America comes from feedlot cattle[1]. On feedlots, the cattle are fed grains, not grass/silage... grains that we humans can easily eat like soy, corn, and barley [2].
1. https://www.huffingtonpost.com/nil-zacharias/its-time-to-end...
2. http://www.goodfoodworld.com/2012/01/grass-fed-vs-feedlot-be...