The effect of pre-weaning housing on the play and agonistic behaviour of domestic pigs

The effect of the pre-weaning housing system on play behaviour before weaning and agonistic behaviour after weaning and during the fattening period was investigated in 32 litters of domestic pigs. Three pre-weaning housing systems were compared: poor crate (standard farrowing crate without straw), enriched crate (crate with straw, 20% larger), and, as a control, a farrowing pen (pen with straw, 60% larger than the poor crate). At the age of 1, 2 and 4 weeks, play behaviour (locomotor and social play) was recorded for 3 h. Four weeks post-partum, piglets were weaned and two litters from the same housing system were mixed in a new pen, with the stocking density corresponding to density in the pre-weaning poor crate. During mixing, the frequency of agonistic behaviour and the proportion of abnormally ended fights (chasing and biting to the hindquarters of the opponent) were recorded for 3 h, and after 6 h, the number of wounds was counted. Four focal pigs from each litter were chosen (two female and two male) and their agonistic interactions were measured during a food competition test at the age of 3 and 6 months. The pre-weaning housing system tended to have an effect on the frequency of locomotor (GLMM, p < 0.1) and social play (GLMM, p < 0.1) with piglets from the more enriched environments playing more frequently. The pre-weaning housing system did not affect the frequency of agonistic behaviour (GLMM, ns), the number of wounds after mixing (GLMM, ns) or the proportion of abnormally ended fights (GLMM, ns). During the food competition tests at 3 and 6 months pigs reared in the enriched pens were much less aggressive than the pigs reared in both types of crates (GLMM, p < 0.01). Our results suggest that the enrichment of the pre-weaning environment through straw and enlarged space probably stimulate pre-weaning play behaviour and substantially reduces the tendency of pigs to behave aggressively during food competition later in life. However, aggression during post-weaning mixing of piglets does not seem to be affected by pre-weaning enrichment.