Cows are fed things like soybeans and corn that humans could be eating directly,
Only in the last stage, the "feeding up" process in feedlots. During most of their lives they eat grass, and if over-wintered in colder areas hay with maybe some grain.
The critical part of the quote you made is:
,
That is, the comma which is followed by an 'or' clause which totally invalidates your refutation.
http://www.smbc-comics.com/index.php?db=comics&id=2393#comic