26. These systems consist of several tiers of perforated platforms formed of wire or plastic mesh or timber slats, built into a laying house; the platforms are often interconnected by ladders or intermediate perches. The ground floor level is usually partially covered with litter. Nest boxes are provided at several levels and, in UK versions, feed and water are available on all platforms. In certain Swiss and Dutch versions, some of which have been imported into the UK, feed is only provided on the lower platforms, the top tier being regarded as a resting area. Most aviaries have manure collection and removal systems included beneath each tier.
27. Although the EC Egg Marketing Regulations (see Appendix D) allow a maximum stocking density of 25 birds/mē of the ground floor area for barn eggs', we understand that most producers stock at a maximum of 15.5 birds/mē as recommended in FAWC's Report on the Welfare of Laying Hens in Colony Systems (1991). Stocking density on the total available surface area is much less, commonly between about 7-11 birds/mē.