A Mathematical Modelling approach to defining factors which influence keel fractures in free range laying hens

Skeletal health in laying hens is a major welfare and economic problem, creating a poor public perception of egg production, and influencing consumer choice. Recent studies showed up to 80% of hens suffer keel bone breakage in free range systems (FRS). So, despite many welfare benefits, FRS present unique and urgent problems. Resolution of this problem is particularly timely, as the 2012 EU ban on battery cage systems requires that 18 million birds be "transferred" to alternative systems, mostly FRS - equating to a further 14 million hens suffering bone breakage each year in the UK. The industry views this as unsustainable, and DEFRA as a major concern. Collisions are believed to be the principle cause of keel fractures; however difficulties in observing breaks as they happen prevent a clear understanding of the critical factors. This study will replicate keel fractures in an ex-vivo impact testing system. Bird factors, e.g. weight, age, keel strength and compliance, and collision factors such as impact energy and material compliance will be mathematically modelled to define which factors influence fracture occurrence and provide a "risk assessment" of fractures in a bird or flock of given characteristics. This model will be validated using live birds in housing environments designed to provide a range of bird and collision variables, and tested against predictions at individual bird and pen level. On-farm studies will determine kinetic energy profiles of particular commercial housing types with widely varying fracture rates to provide a physical measure of housing risk, and to test the model in predicting fractures in commercial settings. The outcomes from this study will allow commercial housing systems to be functionally assessed for their keel breakage risk, and identify key elements of housing or bird physiology that may be modified by producers to reduce fracture rates, thus improving health and welfare, and the sustainability of the UK egg industry.