Cal-Maine Foods (CALM) is the biggest egg producer in the U.S., selling more than 1 billion eggs in the past year — 23% of total domestic shell egg consumption. It has a flock of 33.7 million layers (mature females), pullets (young females) and breeders (male or female chickens used to produce fertile eggs). An outbreak of avian flu in the upper Midwest reduced the supply of U.S. eggs.