Pigs in organic production are in most cases of the same genetic material as in conventional production. These animals are bred for high production in conventional production environments. The question therefore arises: Are these animals suitable for organic production? We investigated sow behaviour, piglet production and GxE interactions for performance traits of pigs in commercial organic and conventional herds and in SLU’s Research herd. When sows farrowed outdoors in huts they started their nest-building activities earlier in relation to farrowing start and performed a higher frequency of nest-building behaviour, than they did when they farrowed indoors in pens. Farrowing duration was shorter and still-birth frequency was lower when sows farrowed in huts rather than in pens. When sows and their piglets were group-housed outdoors during lactation, the sows’ and piglets’ natural weaning process was already well advanced when the herdsman separated sows and piglets. This weaning process was influenced by sow’s body condition and the number of nursing piglets. Piglet mortality was higher in the organic compared with the conventional environment. High levels of piglet mortality reduce piglet welfare why efforts to reduce piglet mortality are required. Oestrus during lactation occurred among group-housed sows in organic herds but not among single-housed sows in conventional herds. Lactational oestrus was more common in fatter sows. Herdsmen in both organic and conventional herds praised sows with good nursing behaviour, weaning large and heavy litters with low piglet mortality. We found weak GxE interactions for growth rate and carcass leanness in organic and conventional pig production environments indicating that with regard to these traits, an organic breeding index based on the existing conventional breeding evaluation would be feasible
