"Say what?" : vocalisation as an indicator of welfare in the domestic laying hen

Animal welfare plays a major role in the societal and scientific debate about the housing of laying hens. In this thesis it is assumed that welfare is good when physiologically an animal functions well. It is also proposed that affective states or feelings motivate an animal to perform behaviours that ensure proper biological functioning. Thwarting or blocking these behaviours impairs functioning and welfare. Emotional expressions, such as vocalisations, could be useful in assessing the welfare state of an animal.

There are indications that a state of frustration, induced by thwarting of behaviour, in laying hens is expressed through a specific vocalisation, thegakel-call.Before the gakel-call can be used as a tool to assess welfare two requirements have to be met: a) frustration is consistently expressed through the gakel-call and b) the intensity of frustration is reflected in the number of gakel-calls or qualitative characteristics.

The experiments in this thesis show that frustration, resulting from the thwarting of feeding, drinking, dustbathing and nesting behaviour, is expressed through the gakel-call. The motivation to feed affects the frustration response and is reflected in a higher number of gakel-calls. Social factors such as an audience-effect and social facilitation influence the gakel-call. The functional significance of these latter findings is discussed.

As yet the gakel-call seems a useful parameter to study the impact of certain elements of a housing system on the frustration response of laying hens. Frustration can be an indicator of the welfare state of an animal and with the use of the gakel-call welfare of laying hens in different housing systems can be assessed.