The requirement for water of growing pigs in large groups has been neglected. Current MAFF recommendations suggest one nipple drinker per 10 pigs, while farmers have often used a ratio of 1 per 20 animals. Neither approach is based on empirical investigation. The relationship between group size and the number of drinking points can not be assumed to be linear. The aim was to assess group size and the two conflicting ratios of drinkers for their effect on welfare, as measured by production performance, drinking and social behaviour.

A total of 640 Large White x Landrace growing pigs (start weight 36kg) were housed in a fully slatted commercial grower house for five weeks. Four replicates were used and each animal was assigned to 1 of 4 treatments in a 2 x 2 factorial design of two group sizes (20 vs 60) and two ratios of nipple drinkers to pigs (1:10 vs 1:20). The groups of 20 comprised of pigs from 3 different pens, while 9 pens contributed to the groups of 60. The floor space per pig was maintained constant across treatments. Nine focal pigs (three each of heavy, medium and light weight) were selected from each pen.