A total ofeight 11-wk trials were conducted to evaluate the productivity and aggression at
grouping ofgrower-f inisher pigs [initial body weight (BW)= 31.8 ± 5.4 kg (mean ± SD), n=2304] in two group size
treatments (18 and 108 pigs pen-1). Pigs were housed on fully-slatted floors, provided one wet/dry feeder space for every
nine pigs, and a floor space allowance of 0.76 m2 pig-1 in both group sizes. The level ofaggression at grouping was
recorded for 2 h starting 0, 24 and 48 h following grouping into small and large groups. Pigs were weighed on weeks 0, 2, 5,
7 and 11, and average daily gain (ADG) was obtained. Average daily feed intake (ADFI) was recorded during two periods
(weeks 2 to 5 and 7 to 11). There was no difference in percentage of time spent on aggression between two group sizes up to
48 h following grouping. ADG for the entire 11-wk trial was affected (2 %) by large group size (0.971 and 0.955 kg d-1 for
groups of 18 and 108, respectively; P<0.05). However, the greatest effect on ADG was observed during the first 2 wk following grouping (0.919 and 0.833 kg d-1 for groups of 18 and 108, respectively; P<0.001). There were no significant effects due to group size on ADFI, feed efficiency, variability in final BW within a pen, carcass traits or mortality and morbidity (P>0.05). In summary, the overall productivity and aggression at grouping did not differ substantially between
group sizes of 18 and 108 pigs pen-1.