H2020 CHICKENSTRESS Project: Variations in stress responsiveness in hens: matching birds to environments

New insights into how and why hens experience stress could lead to more resilient chickens and better-designed housing systems. The move away from enclosed, airtight spaces for hens has led to a range of new housing designs. Some can be considered chicken apartments, with different levels and separate areas for feeding and egg-laying, while others offer outdoor space. While these housing systems are a definite improvement over traditional battery cages (banned in the EU since 2012), identifying the most suitable environments for hens remains a challenge. “We still don’t know for sure which environments are least stressful for birds,” notes Tom Smulders, CHICKENSTRESS project coordinator, from Newcastle University in the UK. Chickens also naturally congregate in small groups.

It is therefore possible that birds instinctively find large housing systems stressful. However, proving this conclusively has proven difficult. Identifying causes of and responses to stress The CHICKENSTRESS project, carried out with support from the Marie Skododowska-Curie Actions programme, sought to identify potential ways to reduce stress in new housing systems. To achieve this, the project combined animal welfare-related questions (e.g., the causes of stress) with more neurobiological approaches. “In terms of how the bird brain regulates stress responses, there is still a lot we don’t know,” explains Smulders. “Early chick rearing and genetics might also influence stress resilience.” This work was divided among a network of doctoral candidates, who addressed specific aspects at both their home and host institutions. Some researchers took a basic neuroscientific approach to better understand how the brain controls the stress response.

Others looked at how stress might affect sleep or how different environments or influences in early childhood might affect behavior. "We know that chronic stress can reduce the number of certain cells in the hippocampus," Smulders adds. "So, the researchers counted these cells to see how their manipulations affected the birds' experience of stress." Brain Development and Stress Levels Although some researchers have not yet completed their work, some interesting findings have emerged. One suggestion is that bringing light into incubation and hatching facilities, which are often constantly dark, might have a positive impact on early brain development. Another project focused on encouraging animal orientation in multi-level housing systems.

Moving LED lights were installed on ramps, encouraging curious chicks to follow them. A chicken coop construction company is looking at ways to incorporate this into its systems. “Another researcher found that the more a cage is enriched with elements that birds can interact with, the more their stress hormone levels are reduced,” says Smulders. Integrating neuroscience with other disciplines These results are very preliminary, but Smulders believes the unique integration of neuroscience with applied science and industry in the project is paying off. Several researchers have landed new projects based on their work on CHICKENSTRESS. “One of these projects focuses on genetics,” says Smulders. “Most of the hens we use have been selected for performance in old-fashioned battery cages. So, there could be a mismatch between genetic selection and current husbandry practices.” This, according to Smulders, underscores the growing influence of neuroscience on animal welfare. "While measuring animal behavior and stress hormones is important, it's recognized that there may be something more subtle going on in the brain," he says.