Evaluation of animal welfare by the self-expression of an anxiety state.

Although mental well-being has long been accepted as an important aspect of animal welfare, the subjective feelings of farm or laboratory animals are regarded as lying beyond the scope of scientific enquiry. We now report that pharmacological conditioning of pigs with a drug, pentylenetetrazole, known to induce anxiety in man, permits investigation of the presence or absence of this psychological state during exposure to a variety of environmental stimuli encountered during normal husbandry. Such pharmacological conditioning therefore provides a valuable means to assess and improve elements of animal welfare and should be applicable to other species that show operant behaviour.