The industrialization of poultry-keeping was made possible by the technological innovations of the late nineteenth century. New artificial incubators made it possible to hatch thousands of chicks at a time. New methods of cold storage, and refrigerated railway cars, meant that poultry farmers could ship meat and eggs to distant urban markets. Mechanized equipment enabled farmers to raise larger and larger flocks. During the 1920s, breeders developed the production strains of White Leghorn, and the Cornish-Rock broiler hybrids. Within a few years, the lines developed by these breeding programs completely dominated poultry farming. In 1934, there were more than 11,000 hatcheries in the United States. Now, a handful of global companies produce highly inbred lines that supply broilers and layers to the poultry industry.