In cage-free commercial housing, chickens are housed in groups of thousands of animals. These numbers stand in stark contrast to the natural group sizes of their wild ancestor, the red jungle fowl, which organises in groups of up to 20 animals. Within the small flocks, the animals establish a so-called ‘pecking order’ characterised by strong hierarchical relationships which are upheld and determined by social interactions. In large groups, however, it is questionable whether a pecking order and/or rank system can be established, as individuals might no longer be able to recognize each other or to keep track of the interactions. Interestingly, hens in the large groups have been shown to engage in less agonistic interactions in large groups, a tendency that appears to stabilize in groups of more than 100 individuals.
Several theories were brought forward to explain why aggression is low in large groups and, although the exact mechanisms remain unclear, chickens appear to change their social strategy with increasing group size towards a more tolerant system. If the change in strategy towards a tolerant system holds true, the question arises why stress and fear-related behavioural problems increase in large groups. Additionally, it remains questionable how social tendencies for dominance or submission within the large groups reflect onto the individual under the premise of a changed social strategy.
With the project at hand, we aim to assess whether large group housing holds socially negative impacts for laying hens. For this purpose, in a first step, we investigate how certain social behavioural profiles are related to a hen’s movement, health, and physical characteristics. In a second step, we will examine whether there is a relationship between the group size and behavioural, physiological, and neurological measured stress responses. The final investigation is aimed to see whether there are subgrouping structures to be found in large groups and if so, how stable these are to changes within the group.
