In order to improve the occupation rate in laying hens held in a single tier floor system, mussel shells (particle size 10-20 mm) were supplied in the litter on every day basis. However, this procedure did not result in any affect on birds’ feather cover, novel object reactions, nor other welfare parameters or production performance. In the present study, it was not possible to partly replace calcium supplementation in the diet with the access to crushed mussel shells. This reduced calcium supplementation in the feed resulted in significantly higher rates of keel bone deviations, lower shell breaking strength and lower dry matter content of feces and litter
