The experiment was performed on 192 piglets, from weaning (28 days) until they were 106 days of age. At weaning, the piglets were separated in groups according to their body mass; 6 piglets were allocated for each box, (0.40 m 2 /piglet). The piglets were weighed at weaning, then at 35 days of age, 64 days and 106 of age, in order to calculate the average daily weight gain. Two boxes of piglets were monitored by video recordings the first 72 hours after weaning and 12 hours when they were 106 days old. Then, from the recordings, we measured the time used for resting, eating, moving and displaying aggressive behaviour. Thus, we noticed that the group hierarchy is established within the first    48 hours after group formation. The stress generated by weaning and parting into groups reflected drastically on the weight gain, especially in the first week after weaning (20% of the growth potential), but also until they were 2 months old (approximately 30% of the growth potential). Improving growth potential after weaning can be obtained by avoiding separation into groups of the piglets from different farrowing boxes, or by keeping piglets in the farrowing boxes until they reach 30-35 kilos. Uniformity in weight and numbers of pigs at weaning facilitates economical use of space in the farm. Another, more practical and economical solution is to avoid the stress generated by establishing the hierarchy among piglets in the group, by smell manipulation or tranquilization after separating into lots.

piglets; behaviour; post-weaning

Presentation: oral