Laying cages typically house from three to eight hens. Feed is delivered to a trough in front of the cage by a chain, and water is supplied by a nipple line or trough line through the cages. In conventional cages, eggs are laid on the sloping wire floor and roll out onto a conveyor belt for collection. Cages are usually arranged in tiers. These are vertically stacked with feces removed by a belt or a scraped shelf between the tiers or arranged stepwise, so that feces fall into a pit. The large number of cages in one house is called a battery of cages, and laying cages are often called battery cages. It is common to have 20,000 birds per house in Europe and 60,000 or more per house in the United States. In the European Union (EU), there has been a statutory minimum space allowance of 85 in2 (550 cm2) per bird since 2003. In the United States most producers are moving toward an allowance of 67 in2 (430 cm2) by 2008, on a voluntary basis. In other coun tries, allowances vary from about 47 in2 (300 cm2) per bird, upward.

High-density housing means relatively low capital cost per bird, and cages have other economic advantages, such as reduction of labor and reduced feed intake because of increased house temperature. Working conditions for operatives are often better than with other systems; dust and ammonia are usually less prevalent. Cages also prevent some behavioral problems of hens. Certain aspects of behavior are controlled, such as egg-laying; there is no need for nest boxes. In addition, social problems associated with large group size, such as aggression and major outbreaks of cannibalism, are reduced. Beak trimming is therefore largely unnecessary, but is still widely practiced.

Reduction of aggression and cannibalism are also beneficial for the birds, and there are additional advantages for hen welfare, notably the separation of birds from their feces and from litter, thus reducing disease and parasitic infections. However, the use of conventional cages has become increasingly controversial, because there are also disadvantages for welfare. Space restriction limits movement and behavior such as wing-flapping, and the lack of appropriate stimuli such as loose material curbs other behavior (e.g., nesting, pecking, scratching). There are also physical effects. Standing on thin wire causes foot damage, and wire cage fronts cause feather abrasion during feeding. Other faults in design sometimes cause birds to become trapped and suffer injury or death. Modern cages have simplified fronts with horizontal bars and often have solid cage sides that reduce feather damage. Injuries are also less prevalent. However, following a report from the Scientific Veterinary Com-mittee,[1] the EU passed a directive that will phase out conventional cages by 2012.[2]

The design of cages for laying hens has been changed often to improve economic performance. More recently, there have also been modifications specifically to ameliorate welfare problems. Perches have negligible cost and encourage normal roosting behavior. An abrasive strip behind the feed trough can reduce the overgrowth of claws. More radically, enriched cages offer increased area and height compared to conventional cages, and also provide a perch, a nest box, and a litter area. Following large-scale adoption of such cages in Sweden, results from commercial flocks are now becoming available. Behavior is more varied than in conventional cages, physical condition is improved, and there has been no cannibalism reported. However, egg production costs are higher, partly because of capital costs and partly because more eggs are downgraded. The EU Directive[2] requires that by 2012 all laying cages shall be enriched, providing 116 in2 (750 cm2) per hen, a nest, a littered area for scratching and pecking, a perch, and a claw-shortening device.

actually go outside. This is partly because cover is rarely provided, despite the fact that chickens evolved in jungles and are cautious of potential predators. Conditions in the house are typical of other floor-housed systems, with feeders, drinkers, and nest boxes for flock sizes varying from several hundred to several thousand. Behavior is more varied than in cages, but as in all noncage systems there is a risk of cannibalism, so birds are usually beak-trimmed.

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