Keel bone lesions in laying hens: occurrence and risk factors

In Europe, farms for laying hens are housing the highest number of caged animals, whereas a transition towards cage-free systems is expected based on the Initiative of the European Citizens “End the Cage Age” and the corresponding Resolution of the European Parliament to provide hens with more possibility of movement, besides other improvements with respect to animal welfare. On the other side, navigation ability of laying hens in alternative systems, with special reference to multi-level aviary systems, may be associated to collisions with equipment and other animals which can produce injuries to animals where and if other risk factors are present. In fact, the latest Scientific Opinion of EFSA about the welfare of laying hens on farm has identified several highly-relevant welfare consequences for these animals based on severity, duration and occurrence, with bone lesions at the top of the list. Among these latter, keel bone fractures have been proved to produce negative states such as pain, distress, and/or discomfort, whereas less data are available on the occurrence of keel bone deviations and their impact on animal welfare and health. In this context, the present contribution aims to provide an overview of the available data about the occurrence of keel bone fractures and deviations in laying hens kept in different rearing systems, discussing the ontogenetic, management and housing factors that have been identified as risk factors, and, finally, to provide information about the animal-based indicators both on farm and slaughterhouse.