Most U.S. meat, poultry, eggs and milk come from so-called factory farms or CAFOs (concentrated animal feeding operations), where thousands of animals are confined indoors. While they efficiently produce abundant supplies of affordable food, CAFOs also raise questions about animal welfare, public health and environmental degradation. Large livestock farms create huge quantities of animal waste, which produce noxious air emissions and contaminate water supplies when storage facilities leak or overflow. Overuse of antibiotics to keep animals healthy in crowded conditions helps generate drug-resistant bacteria and spread infections in humans. And many critics argue that long-term confinement in small enclosures or cages harms farm animals. Organic and free-range meat and eggs are increasingly popular, but they are more expensive than conventional meat and dairy products, and some organic suppliers are adopting industrial-style methods to keep up with demand.

Jennifer Weeks is a freelance writer in Watertown, Mass., who specializes in energy and environmental issues. She has written for The Washington Post, The Boston Globe Magazine, Environment, On Earth and other publications, and spent 15 years as a congressional staffer, lobbyist and public policy analyst. She holds a B.A. from Williams College and master's degrees from the University of North Carolina and Harvard University.