Behind a row of sealed red incubator doors in a new facility in northern China, about 400,000 chicks are hatched every day, part of the rapidly modernizing supply chain in China’s $37 billion egg industry, the world’s biggest. As China overhauls production of everything from pork to milk and vegetables, farmers raising hens for eggs are also shifting from backyards to factory farms, where modern standardized processes are expected to raise quality and safety.That’s an important step in a country where melamine-tainted eggs and eggs with high antibiotic residues have featured in a series of food safety scandals in recent years. It is also spurring demand for higher priced branded eggs over those sold loose in fresh produce markets.