Opportunities for Exercise during Pullet Rearing: Effects on Bone Health and Keel Bone Damage in Laying Hens
This thesis is an investigation of the effect of providing opportunities for exercise on long term bone health of laying hens, with an emphasis on keel bone damage. Osteoporosis in laying hens is a welfare concern as it increases the risk of bone fractures. The keel bone is especially susceptible to fracture during the laying period. Providing opportunities for exercise during pullet rearing, a period of substantial musculoskeletal growth, offers a proactive approach to reducing osteoporosis by stimulating osteogenesis. The main objective was to determine whether rearing environments that offer different opportunities for exercise have long term effects on bone health and keel bone damage of laying hens. A secondary objective was to determine whether adult housing systems that offer different opportunities for exercise have an effect on bone health and keel bone damage of laying hens. Additionally, behavioural differences between hens with or without keel bone fractures were assessed, and an accelerometer to measure inactivity in laying hens was validated. Aviary-reared pullets had greater values for bone cross-sectional area, bone mineral density, bone mineral content, and bone breaking strength in wing and leg bones compared to bones of conventionally-reared pullets. Rearing effects on several bone composition measures were maintained through the end-of-lay, with aviary-reared hens having greater values for bone cross-sectional area and bone mineral content compared to conventionally-reared hens; however, bone mineral density was greater in conventionally-reared hens. Hens in large furnished cages had greater values for bone mineral density and content compared to adult hens housed in conventional cages. Aviary-reared hens had a lower prevalence of keel bone fractures throughout the laying period compared to conventionally-reared hens, with no effect of adult housing. Hens with keel fractures perched more and stood less than hens without keel fractures. Further investigation into whether these behavioural differences cause keel damage, or are a coping strategy resulting from keel damage is warranted. Future studies using the accelerometer validated within this thesis to quantify inactivity levels in laying hens may be useful in measuring changes in activity as a result of keel damage or other pain related conditions in laying hens.