REARING PIGLETS IN A POOR ENVIRONMENT - DEVELOPMENTAL ASPECTS OF SOCIAL STRESS IN PIGS

Effects of rearing conditions on the development of social relationshi ps were investigated in female pigs. For that purpose, one group of pi glets was reared in a poor environment (i.e., a commercially used indo or 4.2-m(2) standard farrowing crate) and the other in an enriched env ironment (i.e., 0.5-ha outdoor pasture with half-open far-rowing crate s). After weaning, all piglets were housed in pairs under standard con ditions. Dominant and subordinate individuals were distinguished withi n pairs and social relationships between members of a pair were studie d in adulthood. The results show that pails reared in a poor environme nt behave more aggressively. The subordinates of these pairs also deve lop symptoms indicative of chronic social stress exposure: i.e., they show a delayed onset of puberty, a smaller daily weight gain, and elev ated basal cortisol levels that are also higher 5 h after an acute res traint stressor (tethering stress). No such deviations were found in s ubordinates reared in an enriched environment. It is concluded that re aring piglets in a poor environment may facilitate the development of social stress in adult (subordinate) pigs. Two underlying mechanisms m ay be proposed: a) deteriorated social skills lead to increased social stress, or b) a failure to cope with stressors in general, and the st ress of being subordinate in particular, occurs in animals reared unde r poor conditions.