Housing conditions alter properties of the tibia and humerus during the laying phase in Lohmann white Leghorn hens

Osteoporosis in caged hens is one driving factor for the United States egg industry to explore options regarding alternative housing systems for laying hens. The aim of our research was to study the influence of housing systems on tibiae and humeri of 77-week-old Lohmann White hens. Pullets raised in an aviary system were either continued in aviary hen systems (AV) or conventional cages (AC) whereas pullets reared in conventional cages continued in conventional hen cages (CC) or enriched colony cages (EN) at 19 weeks. From each group, 120 hens were randomly euthanized and right and left tibae and humeri were excised for structural and mechanical analysis. Volumetric density of the cortical bone was measured using quantitative computed tomography (QCT). Aviary (AV) hens had greater cortical thickness and density but similar outer dimensions to AC hens (P < 0.05). Hens in EN system had humeri with similar cortical thickness and density but wider outer dimensions than the humeri of CC hens (P < 0.05). Cortical geometry of the tibiae was the same for the EN and CC hens, whereas EN hens had denser tibial cortex than CC hens (P < 0.05). Geometrical changes in the humeri suggest that hens in the AV system were better able to protect their structure from endosteal resorption during the laying phase. Humeri of AV and EN hens had increased second moment of area compared to the AC and CC hens; however, the changes were not observed in tibiae. Mechanical property differences were observed, with bones of AV hens having greater failure moment and stiffness than AC hens and the same difference was observed between the EN and CC hens, (P < 0.05). These findings indicate that movement limitation causes loss of bone mass and density whereas provision of moderate movement increases certain bone quality parameters during adulthood in laying hens.