SOCIAL RANK AND FEEDING-BEHAVIOR OF GROUP-HOUSED SOWS FED COMPETITIVELY OR AD-LIBITUM

Certain feeding systems commonly used in practice can result in competition for food and be disadvantageous for low-ranking sows. Feeding a low density diet ad libitum should abolish competition for food and give all sows equal opportunity to obtain food. In this experiment, the consequences of the availability of food on live weight gain and feeding behaviour of sows of different social rank were investigated. Four groups of 12 multiparous sows housed in straw bedded pens were allocated to one of two feeding regimens and remained on treatment throughout gestation. Two groups were floor-fed 3.0 kg per sow of a conventional diet (13.1 MJ (DE) kg-1) once daily, the other two groups received a high-fibre diet (11.2 MJ (DE) kg-1) ad libitum. Dominance ranks were determined in a paired food competition test and from observations of social interactions in the group situation. The paired competition test indicated that the hierarchies in the four pens were almost linear. The hierarchies thus determined were a good representation of feed-related dominance hierarchies in the group situation. When sufficient social interactions were recorded in the group situation, the dominance rank determined from these was similar to the paired competition test. In the ad libitum pens insufficient interactions could be observed in a short time-span. These sows spent, on average, 1.5 h day-1 feeding. They preferred to feed singly, but low-ranking sows had to feed more often at less preferred feeding places and together with other sows. Low-ranking sows gained less weight than high-ranking sows in the floor-fed pens, but not in the ad libitum pens. By changing their feeding strategy, low-ranking sows in an ad libitum feeding system could achieve comparable intake with higher-ranking animals.