How are barn-laid eggs produced?

The large commercial sheds used to produce barn-laid eggs can be more than 100 metres long, 25 metres wide and contain up to 30,000 hens. These sheds are typically multi-tiered so birds can move vertically and use the whole cubic air space inside. The floors can be hard surfaces covered in organic litter like rice hulls or sawdust, or slats or wire mesh.