Battery cages are a housing system used for various animal production methods, but primarily for egg-laying hens. The name arises from the arrangement of rows and columns of identical cages connected together, in a unit, as in an artillery battery. Although the term is usually applied to poultry farming, similar cage systems are used for other animals. Battery cages have generated controversy between advocates for animal rights and industrial producers.
Archaeological evidence from India suggests that Bronze Age people began to domesticate the red jungle fowl around 6,000 years ago. The female jungle fowl has a natural clutch of six eggs, but when an egg is removed she lays another (without the need for fertilization). The modern battery hen lays 250 eggs a year and lives with up to 40,000 others in a windowless house stacked four-deep with cages. Dim light is provided for a constant 17 hours a day to simulate perpetual summer. This stimulates laying, while the low wattage discourages fighting in the confined space. Food and water, with an occasional low dose of antibiotics, are delivered by conveyor belt. Eggs and droppings are similarly removed automatically. Such is the degree of automation that the entire operation on a 300,000-hen farms can be controlled by just three workers. Broiler units are equally efficient. Similar numbers of birds can be grown from day-old chicks to table weight (about two kilos) on four kilos of food in just 41 days. To supply the batteries with laying hens and the meat industry with broilers, intensive hatcheries rear 50,000 chicks a week. Needing no food for at least 24 hours and capable of walking and pecking, the day-old chicks can be easily transported.