32. Many deep litter systems have been improved by the addition of a raised perforated platform. This does not usually increase the surface area but is often elevated and enclosed to form a manure collecting pit; one exception to this is the "roost raft", in which manure collection conveyers are fitted under the perforated floors so that birds can also use the littered area below.
33. Under the EC Egg Marketing Regulations, if the stocking density in this system exceeds 7 birds/mē, the eggs cannot be sold as from deep litter. A frequent arrangement is to have 53% perforated floor and 47% litter area in which case stocking density may be up to 11.7 birds/mē if the eggs are sold as from perchery (barn) systems.