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Variations in stress responsivity in hens: matching birds to environments

Periodic Reporting for period 1 - CHICKENSTRESS (Variations in stress responsivity in hens: matching birds to environments)

Reporting period: 2019-05-01 to 2021-04-30

Egg production is an important sector of animal protein production and public opinion demands that laying hens are kept in the highest possible welfare conditions. In Europe, this has led to a ban on battery cages (European Union Council Directive 1999/74/EC), which came into effect from 2012.This move to cage-free egg production is now spreading around the world, with Europe as a world leader in this field.
Although conceived with the best of intentions and a bold step to improve welfare, unexpected problems have arisen with alternative production systems: in large aviary and free-range systems,more birds suffer from keel bone fractures, there is a resurgence of pathogens associated with venturing outdoors, and there is an increase in feather pecking and cannibalism. Hens without fractures lay more, bigger eggs, and consume less food and water. An outbreak of feather pecking can result in a 5% increase in mortality rates, which could result in 13 billion hens dying prematurely due to feather pecking in the EU annually. It is clear, therefore, that improved welfare can lead to improved productivity.

These new challenges require resolution to keep Europe a leading force in improved animal welfare and production, able to export its expertise. This resolution can only be obtained by bringing together various complementary scientific disciplines with industry stakeholders. Chronic stress is at the core of many of the challenges outlined. It is therefore crucial to understand how hens respond to stress, and to devise strategies to reduce chronic stress in laying hens. Chronic stress is not easy to detect and quantify, because it is essentially an internal response. However, we should be able to measure such an internal response in the animals’ brains.
The objectives of this project are to understand how the stress response is regulated in the avian brain, and to minimize chronic stress by investigating the three main contributors to variation in the stress response: genetic variability, early-life environment, and current environment. By understanding the impacts of these factors, we will be able to produce more stress resilient birds in higher welfare housing conditions, and thereby enhance animal welfare and productivity.

14 ESRs are currently being trained in the scientific study of poultry stress responsivity and in the industrial implementation of conditions that maximize welfare and productivity. Our network uniquely brings together world experts in avian neuroscience with poultry scientists focused on behaviour and stress biology, and with two of the largest companies supplying the poultry industry with birds and with housing systems. The network therefore provides a distinctive training environment which will prepare the ESRs for careers in this industry and the momentous challenges it faces in a changing global landscape. This project is keeping Europe at the cutting edge of this economically very important field and will improve the welfare of billions of animals.
As we have reached the half-way point of the grant period, all ESRs are finishing up their first research projects and starting the next ones. In this initial period, we have identified and characterized novel populations of neurons involved in stress regulation in different parts of the chicken brain (ESR1, 2 and 5), as well as started to question whether a particular cell populations that we know to be indicative of chronic stress actually represents newly-generated neurons, or might represent different cells with high neuroplasticity (ESR13). Data have also been collected in sleep states in the brain, but these are still being analysed (ESR14). We have identified environmental and genetic factors that predict hatchability and stress responsivity (ESR3), as well as networks of gene methylation and expression involved in the stress response (ESR4). Chicks of two different genetic backgrounds have been incubated in either dark or with a circadian cycle, and their behaviour and morphology is being compared (ESR6, ESR8). We have also compared the microcircuits in their hippocampus involved in generating gamma rhythms (ESR7). So far, strong genetic differences have been identified, and a few tentative differences due to incubation regime. We have investigated the effects of hatching chicks on farm rather than in hatcheries (ESR9) and rearing them in different housing conditions (ESR11), as well as providing physical ways to guide them through a multi-level housing system (ESR10). Finally, individual animals have been tracked and followed, and their space use is being related to different welfare indicators (ESR12).
All ESRs are researching new questions, and therefore are per definition going beyond the state of the art. ESR1 is characterizing which cell populations make up the avian amygdala; ESR2 is identifying 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.

Expected Results until the end of the project
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
The project has had little impact so far, as most of the first studies are still being analysed. However, 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.