Preparing for life: effects of environmental choice and change during rearing on adaptability in laying hens

The importance of the early environment for later animal behaviour, health and welfare is well known. Hens (Gallus gallus domesticus) kept for egg production are exposed to various challenges and opportunities during their life time, such as relocation from a rearing to a laying facility or access to free range. Promoting greater adaptability in young laying hens could lead to improved welfare, especially considering the increasing complexity of commercial loose housing and aviary systems. However, early environmental inputs that could improve laying hen adaptability have not been clearly identified. This thesis investigated the impact of two environmental inputs (“choice” and “change”) during rearing, based upon well-established theories on the effects of controllability and predictability on coping ability. Experiments using two relevant environmental resources, litter and perches, showed that young laying hens with regular changes of litter and perch type were less fearful when placed in a novel environment. Young laying hens given the option to choose between different litter and perch types during rearing, showed increased exploration in a novel environment, were better able to locate a hidden feed reward and showed improved stress coping and immunocompetence. Both short- and long-term effects were seen among hens reared with different levels of environmental choice and change, depending on the stage of rearing in which hens were exposed to the environments and when the evaluations were conducted. In particular, providing greater possibilities for environmental choice could be a biologically relevant approach for a rearing environment that goes beyond simply providing basic resources and can enhance laying hen adaptability and welfare.