Poor rearing conditions and social stress in pigs: repeated social challenge and the effect on behavioural and physiological responses to stressors.

Effects of rearing condition on behavioural and physiological reaction to social confrontations and to social and non-social stressors were studied in female pigs. The pigs were reared under either poor (the standard farrowing crate) or enriched (group of free-ranging sows with piglets) conditions. At the age of 14-17 weeks, the pigs were exposed to a series of social confrontations where an intruder was introduced into the home pen of a resident. The results show the presence of a clear difference in terms of aggressive behaviour between residents and intruders from enriched but not from poor rearing conditions. Furthermore pigs reared under poor conditions inflicted more wounds on each other. We suggest that this reflects a difficulty in establishing a dominance relationship in poorly reared pigs, caused by impaired development of social skills in these pigs. Subsequently, reaction to novel object, non-social and social stress was measured in adult age, showing that the effects of rearing conditions are long-lasting, and give rise to differences in reaction to challenges in that pigs from enriched rearing conditions showed more avoidance behaviour than pigs from poor rearing conditions.