Science-based assessment of animal welfare: farm animals.

Animal welfare is to do with the feelings experienced by animals: the absence of strong negative feelings, usually called suffering, and (probably) the presence of positive feelings, usually called pleasure. In any assessment of welfare, it is these feelings that should be assessed. Because feelings are subjective, they cannot be investigated directly. However, there are indirect methods by which animals can be 'asked' what they feel about the conditions under which they are kept and the procedures to which they are subjected. These methods involve preference tests, followed up by motivational tests to assess how important the animal's choice is. Measurements of impaired biological functioning, particularly those connected to decreased health and increased physiological stress responses, can provide good corroborating evidence that welfare is compromised.