Aggression among finishing pigs following mixing in kennelled and unkennelled accommodation

This study examines the interactive effects of mixing and the provision of kennels to finishing pigs on agonistic behaviour. Pigs were housed either in naturally ventilated kennelled accommodation, or in an unkennelled sloping floor accommodation with automatically controlled natural ventilation (ACNV). Under each of these two housing conditions, three groups of 10 pigs were subjected to one of the following four mixing/moving treatments: no mixing (control), mixing and moving at 55 kg only, mixing and moving at 75 kg only and mixing and moving on both occasions. Groups which were not mixed at 55 kg or at 75 kg were moved to a novel pen at the time that the others were mixed. Mixing and moving pigs resulted in higher levels of aggression and skin damage compared to moving only. Levels of skin lesions were lower when mixing at 55 kg compared to mixing at 75 kg. The duration and frequency of fights in the immediate post mixing period and skin damage measured on day 1 after mixing correlated well when mixing pigs at 75 kg, but not when mixing at 55 kg. This suggests that the hierarchy takes longer to be established in younger pigs than it does in older heavier pigs, or that skin damage inflicted by heavier pigs during fights is more severe. Previous mixing at 55 kg had minimal effects on mixing at 75 kg in terms of behaviour immediately post mixing and skin lesions in the following two days. The presence of a kennel appeared to have a positive effect on the average duration of fights, but the effect on the proportion of fights which involved location changes (lying to dunging area or vice versa) was not significant. Performance data suggested that food conversion ratios were poorer in the first two weeks after mixing in the kennelled building, but not in the sloping floor building. Increased social and thermal stress after mixing in the kennelled, naturally ventilated accommodation may have been the cause of this. Over the whole of the finishing period, daily live weight gains and food conversion ratios did not differ measurably between treatments. (C) 2000 Elsevier Science B.V. All rights reserved.