How important is natural behaviour in animal farming systems?

It is often assumed and demanded that for a good welfare, farm animals should be given "the freedom to express their natural behaviour". This demand is problematic for at least two reasons. First, natural behaviour is difficult to delineate because of its variability and flexibility. Second, some behavioural patterns that are clearly natural are in fact detrimental to animal welfare. These include emergency behaviours such as flight reactions that bring the animal into a state of stress without achieving the goal for which the behaviour had evolved; and damaging behaviours such as rank-related or illness-related aggression during which animals inflict injuries or deprive their penmates of resources. Nevertheless, when these reservations are taken into account, opening possibilities for natural behaviour may be useful as guidance for improving the existing husbandry systems. Specifically, providing the farm environment with the key features towards which the behaviour was originally adapted brings three classes of benefits. First, it is often more efficient to allow animals to satisfy their own needs and achieve their goals than to address these needs and goals through technical means. Second, a large class of natural behaviours is associated with positive affective experience, and thus their performance directly enhances animal welfare. Third, the performance of natural behaviour in its richness and complexity often brings long-term benefits for the animal, such as improved proficiency in coping with social and physical challenges. Thus, while the freedom to perform the whole repertoire of natural behaviour is not per se crucial for farm animal welfare, the opportunity to perform natural behaviour may be an effective way improve their welfare in practice immediately, and a promising basis for the design of husbandry systems for the future. (c) 2006 Elsevier B.V. All rights reserved.