When it comes to cows, we keep hearing that grass-fed is better than grain-fed. Better for us, better for the cows, better for the environment. Farmers have grazed their cows on grass for centuries, with no need for bovine growth hormones, and no outbreaks of mad cow disease or E. coli.

But the factory farms most of our beef comes from these days aren't really farms at all; they're industrial indoor feedlots called Concentrated Animal Feeding Operations, or CAFO's.