Variations in stress responsivity in hens: matching birds to environments

Because of the high demand for eggs, large numbers of hens are farmed in modern egg production. Because of the intensity of this form of farming, the public has justifiably been concerned about the welfare of these birds. Higher welfare also leads to higher quality eggs, higher productivity, and lower incidence of disease and therefore lower need
for antibiotics. Our project aimed to reduce the chronic stress experienced by hens. To this end, we investigated the neurobiological, genetic and developmental factors that lead to higher stress resilience, and the environmental (housing) factors that lead to chronic stress. Europe has led the world in hen welfare with the complete ban of battery cages (European
Union Council Directive 1999/74/EC). However, the replacement housing systems have their own potential welfare challenges. Our goal was to identify these challenges and develop improvements for implementation by industry.
We trained a new generation of innovative and entrepreneurial early-stage researchers, able to face different challenges related to poultry farming and to apply scientific knowledge and ideas to products and services for economic and social benefit. We constituted an international network of groups with expertise in avian
brain research, genetics, welfare and egg farming. The training was complemented by secondments in different laboratories of the network, workshops, and industrial secondments in the poultry industry. The new generation of professionals applied this knowledge and experience to improve poultry housing systems, welfare, and product quality, which will grow the sector's resilience in addressing growing societal demands for higher animal welfare and healthier diets. Moreover, they will contribute to strengthen Europe's human capital in R&I,
increase Europe's attractiveness as a leading research destination, improve Europe's competitiveness and growth, and engage in an improved knowledge-based economy and society.

The ChickenStress network has integrated neurobiology into the assessment of which factors cause stress in laying hens, and which factors can reduce the experience of stress. We have identified genes relating to individual differences in stress susceptibility, as well as genetic and neurobiological markers of the experience of stress. We have identified that light during incubation may not change welfare much, but that avoiding transport of chicks and potentially providing litter and food upon hatching may have beneficial effects. Rearing the animals in complex environments, better matched to the adult laying environment also has clear benefits. Finally, birds seem to be less stressed in large than small social groups, potentially relieving the concern about the size of the social group in cage-free housing (although we need to extend this beyond 120 birds). More enrichment reduces fearfulness, at least in large furnished cages.
We look forward to working with others in the future to continue to apply our new approach to other questions of laying stress resilience and welfare.

All ESRs were researching new questions, and therefore are per definition going beyond the state of the art. ESR1 is characterised which cell populations make up the avian amygdala; ESR2 identified which cell populations in the hippocampal formation respond to stress; ESR3 has identified genetic factors that are involved in stress responsivity; ESR4 has found candidate genes involved in stress responses; ESR5 has described expression patterns of different peptides in the avian amygdala; ESR6 and ESR7 have found tentative new evidence for the role of light during incubation; ESR8 is finalizing new technology for tracking birds outside; ESR10 had identified LEDs as the most salient stimulus for chicks to follow up and down ramps; ESR11 has found effects of early life spatial environment on late life spatial abilities; ESR13 has discovered that the DCX protein is expressed in neurons that are not newly generated neurons; and ESR14 has recorded sleep signals in hens for the first time.

ESR1: characterization of embryonic origin, connectivity, and activity of avian amygdala cells involved in stress regulation
ESR2: characterization of location, connectivity and function of avian hippocampal cells in regulating the HPA axis
ESR3: genetic and environmental predictors of stress responsivity and productivity
ESR4: genetic networks involved in regulating the stress response
ESR5: genetic networks operating within the avian amygdala
ESR6: effects of light during incubation on stress responsiveness and cognition in later life
ESR7: effects of light during incubation on the properties of microcircuits in the avian hippocampus
ESR8: effects of light during incubation and food enrichment on range use
ESR9: effects of on-farm hatching on cognition, behaviour and stress responsivity
ESR10: rearing recommendations to improve full space use with fewer accidents in adulthood
ESR11: effects of early rearing environment on cognition and stress resilience in adulthood
ESR12: individual variation in tier use in commercial aviaries
ESR13: distinction between newly-generated neurons and other neural plasticity in the avian hippocampus, and their response to stress
ESR14: understanding of the effect of stress on sleep quality and markers to measure this non-invasively.

Potential Impact
There is a strong potential for especially projects relating to genetic background and to early-life rearing environment to result in strong recommendations to the poultry industry to improve genetic selection and rearing conditions to match birds to adult housing environments.

Periodic Reporting for period 2 - CHICKENSTRESS (Variations in stress responsivity in hens: matching birds to environments)

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