The use of demand functions to assess behavioural priorities in farm animals
The use of demand functions to identify the behaviours most important to animals has been advocated widely. The principle is to place increasing cost on the opportunity to perform several behaviours and subsequently to rank these behaviours according to the change in their performance
as a function of cost; this change is described by the elasticity of the demand function. However, the method has been criticised for placing the animal in too artificial a setting. Firstly, the animal works repeatedly for short periods of access to a resource, which may interrupt bouts of
behaviour; secondly, animals are tested in isolation, which may affect their motivation to perform the target behaviour; and, finally, assumptions regarding the effect of prior deprivation and reward duration on elasticity of demand need to be tested. This criticism, however, is important
only if these factors do affect the elasticity of the resulting demand function. This paper reviews experiments that have developed methods to assess the importance of various behaviours to farm animals and that have tested the effect of social context, length of deprivation of a resource
and reward duration. It is concluded that the elasticity of demand function may be used to assess the relative importance of various behaviours, but that it is important to make sure that the experimental set-up yields valid estimates of the elasticity of demand.