Animals living in a group generally establish a dominance hierarchy which enables the group to function without the necessity of fights whenever group members encounter each other (Beilharz and Cox, 1967). A stable dominance hierarchy can be maintained by subtle signals and give high-ranking animals priority of access to resources in limited availability (Banks et al., 1979). In intensive housing systems this can have serious consequences for low-ranking animals (Csermely and Wood-Gush, 1990), owing to close proximity of high-ranking sows and, in some cases, limitation of resources.

A restricted feeding regimen is adopted in commercial practice to maintain an almost constant body-condition of the sow throughout the reproductive cycle. Depending on the manner of distribution of this limited amount of food between sows in a group-housing situation, competition can result in unequal distribution of food and loss of condition of low-ranking sows (Brouns and Edwards, 1992 ). This kind of competition is likely to occur in feeding systems where the food is distributed once or twice daily on the floor (floor-feeding) and is aggravated by a low feeding level (McBride et al., 1964; Baxter, 1983 ). A  conventional diet is concentrated in nutrients and although it is sufficient for good health and performance, it might not fulfil other needs of the sow, since the small amount of food is unlikely to give a feeling of satiety (Lawrence et al., 1988 ). Provision of
a diet ad libitum should, in theory, obviate the need for competition and eliminate negative consequences for low-ranking sows.
In this experiment, the consequences of food available, in limited quantities once daily or ad libitum, on live weight gain and feeding behaviour of sows of different social rank in a group-housing situation, were investigated.

Sandra Edwards