If you are interested in our food supply read the fantastic book called "the omnivore's dilemma"
the author follows the entire path of both corn and beef from inception through growing harvesting processing selling and eventually our plate. amazing book.
in this book he says while industrial beef producers have stopped feeding cow protein to cows, they still feed cow fat to cows. they believe this is safe. they also feed chicken shit and chicken feathers to cows as feed.