Physiology, Endocrinology and Reproduction II

Susceptibility of caged layers to osteoporosis and cage layer fatigue has prompted the switch from conventional caging to more extensive systems allowing birds to perform load bearing activities. However, high incidences of fractures have been reported in these alternative housing systems. The aim of this study was to determine the housing system and strain effects on bone quality parameters: bone weight, ash content, cortical bone density (CBD), cortical thickness (CBT), and keel bone deformities. Tibia, femur and keel of Hy-Line Brown (HL), Hy-Line Silver Brown (HS) and Barred Plymouth Rock (PR) hens housed in conventional cages (CC), cage-free (CF) and cage-free with range (outdoor access) (R) were studied. Sixty hens from each strain and housing system combination were euthanized and bones were excised for analysis. Quantitative CT (QCT) was used to measure CBD and CBT in each bone. Three dimensional images of keels were generated using QCT scans to score and analyze the deformities. CBD in all 3 bones was significantly higher (P < 0.05) in PR compared with HL and HS. There was no effect of housing system for femur CBD, but CBD was significantly higher (P < 0.05) for middle and distal tibia of birds housed in R compared with CC. CBD for keel bone was significantly higher (P < 0.05) in CF and R birds compared with CC birds. CBT of tibia was significantly higher (P < 0.01) in PR compared with other 2 strains. CBT was also high (P < 0.05) for mid and distal tibia for birds housed in R and CF compared with CC. Bone dry weight and ash content were higher for PR. Birds housed in R and CF were significantly heavier (P < 0.05) compared with CC. Average keel deformity score was not significantly different among the groups. However, each housing system was associated with high prevalence (>90%) of keel deformities. These findings indicate that there are differences among strains in terms of bone quality. Further, it suggests that range and cage free housing may have beneficial impact on tibia and keel bone integrity compared with conventional cages but may not be sufficient to prevent fractures or deformities, particularly of keel.