Bone strength and keel bone status of two layer strains kept in small group housing systems with different perch configurations and group sizes.

The objective of the present study was to investigate whether an arrangement of perches at two different heights within individual compartments of small group systems (back perch elevated (BE), front perch elevated (FE) or both perches heightened (FBE)) combined with an enlarged group size would increase humerus and tibia bone breaking strength and impact keel bone status. Bone strength and keel bone status of two layer strains (LSL, LB) kept in small group systems (SG 40-60 (40, 60 hens), SG 20-30 (20, 30 hens) with different perch configurations) and furnished cages (FC, 10, 20 hens, perches in standard position) were compared in two trials. Investigations were carried out in the laying months 6 and 12, comprising a total of 576 hens. When all compartments of SG 40-60 had been incorporated with perches at two different heights, humerus and tibia bone strength in LSL layers significantly increased compared to FC, whereas keel bone status was negatively impacted. Within SG 40-60, BE and FE perches significantly increased humerus strength in LSL layers compared to FBE perches. LB layers had significantly higher bone strength in groups of 20 compared to 30 hens in SG 20-30, whereas no effect of group size was detected for LSL hens. Keeping hens in SG 40-60 with modified perch positions was associated with increased bone strength but brought about the problem of inferior keel bone status.