Motivation for group housing in gestating sows

It has been argued that the welfare of gestating sows is higher in groups than singly in stalls, in part because group housing offers them more space and social contact. This study set out to ascertain how important access to a group pen was to dominant sows housed in stalls, using a measure of motivation. Subjects were trained to perform a panel-pressing task, then housed in a stall and permitted each day to work for a day's access to a fully slatted group pen containing two familiar, subordinate sows at a stocking density of 2.7m(2) per pig. Social ranking was determined by observations at mixing and from feed competition tests. The fixed-ratio schedule was increased daily and the highest schedule reached (the reservation price) was used as a measure of motivational strength. To interpret this measure, it was compared with the highest schedule that subjects reached when working for access to the lost 1/16(th) of their estimated ad libitum daily food intake after having consumed the first 15/16(ths) free. Sixteen subjects were tested, eight working for access to the group pen first and eight for access to the food first. Seven subjects yielded useable data: four reached a higher schedule working for food and three reached a higher schedule working for the group pen. Overall, subjects attached no more importance to a day's access to the group pen than to the lost 1/16(th) of their estimated ad libitum food intake. It is likely that the subjects were close to satiation when working for food because consumption frequently fell substantially short of the 'ad libitum' allowance. These results suggest that dominant stall-housed sows are only weakly motivated to gain access to a fully slatted group pen, although motivation might be higher when deprived of access to the group pen for longer than one day, if tested at a different time of day or if the quality of the group space was improved, these three possibilities still need to be tested.