Intensive pig farming, also known as pig factory farming, is a system of pig production in which pigs are raised indoors at high density under controlled environmental conditions. It has become the dominant method of commercial pork production in most industrialized countries, though traditional systems remain significant in many parts of the world. Typical facilities, sometimes called piggeries, house pigs raised for slaughter in group pens on slatted floors made of concrete, with a manure pit beneath the floor. Breeding sows are kept in gestation crates or in group housing during pregnancy, and moved to farrowing crates to give birth and nurse piglets. The waste falling through the slats is sometimes transferred to manure lagoons.