Several systems are available that allow birds the run of a house, but without access to the outdoors. Some have attempted to use wholly slatted or wire floors, but these result in many behavioral problems including floor laying, cannibalism, and hysteria. Strawyards are often converted from existing farm buildings, partially open and therefore having natural light and ventilation, with straw as litter. Deep-litter houses use wood shavings or other material such as sand, corncobs, or peanut hulls as litter and they are usually more fully enclosed. With automatic ventilation, this allows more precise temperature control. In many cases, natural light is also excluded to allow the use of photoperiods shorter than day length. For this reason, deep litter is often used for the rearing of poultry, even if they are to be housed in a different system later.
In any litter-based system, birds defecate on the litter. Under good conditions, feces are dispersed partly by hens pecking and scratching dry out, and are broken down by bacterial action, allowing the litter to remain friable. If the litter becomes wet, packed solid, or both, however, unpleasant conditions develop, including high ammonia. Foot damage and disease are likely. Management of nesting is also important early in the laying period to ensure that hens are laying in nest boxes rather than on the floor, and later to identify and discourage broodiness. Various methods of automatic egg collection from nests are possible. Feeders are either pans supplied by augers, or troughs supplied by a chain, while water is provided in a nipple line or in bell-shaped, gravity-fed drinkers.
Stocking density can be higher if part of the floor area is slats or wire mesh, so that fewer droppings accumulate in the litter. Drinkers placed over the slats reduce the risk of wet litter. However, sale of eggs as deep-litter eggs in the EU limits stocking density to 6 birds per yd2 (7 per m2), with at least a third of the floor as litter (Table 1). Other systems increase the density of birds in the house by using multiple levels. The aviary uses tiers of slats or mesh to increase the use of vertical space in the house. Drinkers are placed over slats and feeders are widely distributed. Nest boxes are made as accessible as possible, but floor laying is sometimes a problem. Various arrangements of tiers have allowed experimental stocking densities of up to 19 birds per yd2 (22 per m2) of floor space. Group size is commonly about 1000 birds. The perchery provides perches on a frame so that birds can jump up or down. Percheries that provide litter generally have good results, but EU requirements for perchery eggs allow up to 21 birds per yd2 (25 per m2) and do not include a provision for litter (Table 1). Without litter, birds do not use the floor fully, and the minimal requirement of 6 in (15 cm) of perch space per bird does not provide complete freedom of movement. Commercial farms applying these standards have encountered problems such as cannibalism and nonlaying birds occupying nest boxes.
The tiered wire floor system developed in The Netherlands resembles a cage house with the partitions removed. There are rows of narrow tiers, with passages in between the rows, and a manure belt under each tier. Nest boxes are against the wall, perches are mounted over the top tier, and feed and water are supplied at all other levels except the floor, which is covered with litter. This and other variants of aviaries and percheries are almost universal in Switzerland, the only country in which laying cages have been banned. Another development in Switzerland has been the combination of these systems with either free range or a terrace along the side of the house, with open-mesh walls. With relatively small flocks, free-range birds use the outside area extensively, and terraces are also well used.
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