Influence of group size during the post-weaning period on the performance and behaviour of pigs

Abstract

The aim of this study was to assess the effect of group size during the post-weaning period on the performance and behaviour of pigs. A total of 1280 pigs were allocated to one of five group sizes from weaning at 4 weeks of age until 10 weeks of age. The group sizes consisted of 10, 20, 30, 40 or 60 pigs, and groups were balanced for gender and weight. All pigs were housed at a constant space allowance and one 4-space dry feeder and drinker was provided per 10 animals. Group size did not significantly affect growth rate; however, the coefficient of variation for growth was greater in groups of 10 than in larger groups, and this reached significance ( P<0.05) with all group sizes except groups of 30 pigs. Feed intake was not significantly affected by group size; however, food conversion tended to be poorer in groups of 40 and 60 pigs than in smaller group sizes ( P<0.06). Behavioural observations showed no difference between treatments in the proportion of small, medium and large sized pigs at the feeder, or in the total number of pigs at the feeder. In addition, overall levels of aggressive behaviour at the feeder did not differ significantly between treatments. At 10 weeks of age, the pigs were moved to finishing accommodation where they were housed in groups of 20. The effect on performance of splitting groups of 40 or 60 pigs into groups of 20 pigs was assessed. Food conversion ratio was poorer in groups split from groups of 60 pigs than in groups split from groups of 40 pigs, or in groups which were kept in a group size of 20 pigs throughout the growing and finishing stages ( P<0.05). These results suggest that the group size of weaned pigs can be increased from 10 to 60 animals without any significant adverse effects on performance or welfare during the post-weaning period. There may be some benefits of increasing group size to more than 10 animals in terms of reducing variation in growth rate. If pigs are to be housed in groups of 20 during the finishing period than it may be better to house pigs in groups of 40 rather than in groups of 60 pigs during the post-weaning period, in order to reduce negative effects on food conversion during the finishing period.