Influence of housing systems on bone properties of laying hens

Osteoporosis in caged hens is one driving factor for the U. S. egg industry to explore options regarding alternative housing systems for laying hens. The aim of this dissertation was to determine the housing system effects on bone quality of laying hens. The first study looked at tibiae and humeri of White Leghorn pullets reared in conventional cages (CC) and a cage-free aviary system (AV). At 16 wk, 120 birds were randomly sampled from each housing system for bone property analysis. Humeri and distal tibiae cortical density was greater in AV pullets compared to CC pullets (P < 0.05). Tibiae and humeri of AV pullets had a thicker cortex than the CC pullets (P < 0.05). Additionally, the tibiae and humeri of AV pullets had greater (P < 0.05) second moment of areas than the CC pullets. The aim of the second experiment was to study the influence of housing systems on 77 wk White Leghorn 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 wk. From each group, 120 hens were sampled at random for bone property analysis. 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 humeri of CC hens (P < 0.05). The follow-up study aimed at analyzing age-related changes in bone properties in different commercial housing systems. Pullets reared in conventional cages (CC) were continued in CC or moved to enriched colony cages (EN) at 19 wk whereas those reared in cage-free aviary (AV) were moved to AV hen houses. Bone samples were collected from 60 hens at 18 and 72 wk and 30 hens at 26 and 56 wk from each housing system. AV pullets had 41% greater humeri and 19% greater tibiae cortical area than CC pullets (P < 0.05). Humeri and tibiae of AV pullets had greater stiffness (31% and 7% respectively). The geometrical and biomechanical differences between bones of AV and CC hens persisted throughout the laying cycle. Moving CC pullets to EN resulted in decreased endosteal resorption in humeri evident by 7.5% greater cortical area of EN hens (P < 0.05). Stiffness increased with age in both tibiae and humeri while energy to failure decreased. The final study was aimed at determining the housing system and strain effects on bone quality parameters. Tibia, femur, and keel of Hy-Line Brown (HB), Hy-Line Silver Brown (SB) and Barred Plymouth Rock (BR) hens housed in conventional cages (CC), cage-free (CF) and cage-free with range access (R) were studied. Bone samples were collected from sixty hens from each strain and housing combination for analysis. Tibia cortical thickness was greater (P < 0.01) in BR than HB and SB. Between housing systems, thickness was greater (P < 0.05) for mid and distal tibia for R and CF compared to CC. Tibiae and femoral cortex were denser (P < 0.05) in BR compared to HB and SB. Keel bone density was greater (P < 0.05) in CF and R birds compared to CC birds. Each housing system was associated with high prevalence (> 90%) of keel deformities and the housing and genotype influenced the type of deformity. These findings indicate that range and cage-free housing may have beneficial impact on tibia and keel bone integrity compared to conventional cages but the improvement may not be sufficient to prevent fractures or deformities, particularly of keel.