The economic logic of gathering so many animals together to feed them cheap corn in CAFOs is hard to argue with; it has made meat, which used to be a special occasion in most American homes, so cheap and abundant that many of us now eat it three times a day. Not so compelling is the biological logic behind this cheap meat. Already in their short history CAFOs have produced more than their share of environmental and health problems: polluted water and air, toxic wastes, novel and deadly pathogens.

Raising animals on old-fashioned mixed farms... used to make simple biological sense: You can feed them the waste products of your crops, and you can feed their waste products to your crops. In fact, when animals live on farms the very idea of waste ceases to exists; what you have instead is a closed ecological loop—what in retrospect you might call a solution.

—Michael Pollan, The Omnivore's Dilemma