Early experience of a complex environment can improve biologically relevant traits related to coping abilities. However, the mechanisms underlying these positive effects have not been well explored. We hypothesized that giving chicks possibilities to express choices within relevant resources could be an important part of the mechanism, as well as a novel way to increase environmental complexity. In a balanced design, laying hen hatchlings of the white hybrid Bovans Robust were reared in a “single-choice” environment (single litter and perch type) or a “multi-choice” environment (four different litter and perch types). Immunological and behavioral indicators of chicks’ coping abilities were explored in this experimental study at three weeks of age. Chicks from “multi-choice” environments had shorter durations of tonic immobility, lower heterophil/lymphocyte ratios, higher natural antibody concentrations, and were more successful in gaining novel food rewards in a repeated opportunity test. These results imply that chicks having access to variation within resource types were less fearful, experienced less chronic stress, would be more able to cope with pathogenic challenges, and potentially had an improved learning ability. To conclude, the more complex environment, achieved by increasing chicks’ possibilities to choose, seemed to make chicks better prepared for potential challenges, boosting their adaptive capacities and their ability to make the most of opportunities.
Laying hens are typically moved to a novel environment after rearing, requiring adaptability to cope with change. We hypothesized that the standard rearing of laying hen chicks, in non-changing environments with limited choices (a single variant of each resource), impairs their ability to learn new routines, use new equipment and exploit new resources. On the contrary, rearing in a changing environment that also offers a choice of resource variants could better prepare chicks for the unexpected. To explore this hypothesis, environmental change and choice were manipulated in a 2 × 2 factorial experiment. Compared to standard rearing, greater change during early rearing, through repeatedly swapping litter and perch types, reduced initial freezing when exposed to a novel environment suggesting a lower fear response. Greater choice during rearing, through simultaneous access to multiple litter and perch types, resulted in shorter latencies to solve a detour task, more movement in novel environments and less spatial clustering, suggesting improved spatial skills and higher exploration. However, combining both change and choice did not generally result in greater improvement relative to providing one or the other alone. We conclude that environmental change and choice during rearing have different positive but non-synergistic effects on later adaptability potential.
Early experience of a complex environment can improve biologically relevant traits related to coping abilities. However, the mechanisms underlying these positive effects are not well explored. We hypothesised that the possibility to express a choice, leading to increased control over the environment, could play an important role. In a balanced design, laying hen hatchlings were reared either in a ‘No-Choice’ environment (single litter and perch type) or a ‘Choice’ environment (four different litter and perch types). Immunological and behavioural indicators of birds’ coping abilities were explored at three weeks of age. Chicks from Choice environments had higher natural antibody titres, lower H/L ratios, required more attempts for tonic immobility induction and were more successful gaining novel food rewards in a repeated challenge test. Results imply that their improved natural immune response better prepared Choice chicks for coping with pathogenic challenges, that they experienced less chronic stress and were less fearful. To conclude, the increased potential for control and stimulation arising from making decisions in an early complex environment seemed to better prepare birds for a variety of challenges to come, boosting their adaptive capacities and their ability to make the most of opportunities.
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.
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