Factory livestock farms are spreading across rural America, raising concerns about environmental damage and health risks for people living nearby. An industry once based on small, independent farms is evolving into large operations housing thousands of animals under one roof. The change is helping make beef, poultry and pork more affordable. But animal waste from the mega-farms has fouled waters. The enclosures spew air pollutants that promote climate change and are implicated in illnesses such as asthma. The stench of manure can make life miserable for people nearby. The spread of corporate animal farms is turning neighbor against neighbor in town halls and courtrooms across rural America. Iowa is a major battleground as the top U.S. producer of swine and egg-laying chickens.