What is the information about a cow that eats corn instead of grass?

The FRONTLINE interview with Michael Pollan could open eyes.

-- corn is not what cows should eat.
-- cows are a miracle machine for processing grass into protein
-- e. coli generally dies in a cows stomach when fed grass
-- cows usually take 4 years to macture, but when grown on corn, cows can be harvested at 14 or 18 months.

Read the full interview at "michael pollan frontline interview"

Here's a photo of a feedlot