EFFECTS OF PEN SIZE SHAPE AND DESIGN ON AGGRESSION WHEN GROUPING UNFAMILIAR ADULT-PIGS

The effects of space allowance/pen shape (small square or small rectangular pens providing a space allowance of 1.4 m2 per pig and a large pen providing a space allowance of 3.4 M2 per pig) and pen design (partial stalls, 0.44 m wide X 0.74 m long, or no stalls) on aggression when grouping four unfamiliar adult ovariectomized pigs were examined in an experiment involving 24 pigs that was replicated five times. Aggression was observed for 90 min immediately following grouping and for 40-min periods, around feeding, on the day following grouping and 9 days later. Social behaviour and spatial use of the pens were also determined during a 60-min period between 14:00 and 16:00 h on the day following grouping and 9 days later. Aggressive interactions and the consequent retaliations were significantly lower during the period of 15-90 min after grouping in the small rectangular pens (P<0.05); the presence of stalls had no effects at this time. There were no effects of treatment on aggressive behaviours during the initial 15 min of grouping (P>0.05). Treatment significantly affected social behaviour and spatial use of the pen during a 'rest period'. On the day following grouping in small rectangular pens lying alone behaviour and standing were reduced, and concurrent lying and use of stalls (when present) were increased. In conclusion, this experiment has shown that there may be potential advantages to the welfare of adult pigs in reducing aggression around grouping by grouping unfamiliar pigs in rectangular pens with a space allowance of 1.4 m2 per pig compared with similar sized square pens or pens with a larger space allowance.