Consequences of environmental enrichment on the sexual and behavioural development of entire and castrated male pigsRearing entire male pigs may lead to welfare problems due to their sexual development. Enriching the environment could help toreduce these problems. To test this hypothesis, eighty males (groups of 10) were studied: 40 surgically castrated at 5‐6 days of ageand 40 left entire. Half of each sex type was reared in a conventional environment (1 m²/animal, slatted floor) and the other halfin an enriched environment (2.5m²/animal, straw and outdoor run). Aggressive acts (knocks, biting…) and sexual acts werecounted for one hour, three times a month, from 3 to 5 months of age. Skin lesions were counted the day before theseobservations. Plasma testosterone was also assessed at 90, 120 and 153 days. Testosterone level was higher in entire males thanin castrates (P<0.05), and was not influenced by the environment (P>0.05). Entire males tended to be more aggressive thancastrates at 3 months of age (P=0.06), with aggressiveness decreasing thereafter. Enriching the environment led to a decrease inaggressiveness of castrates (P<0.05), and a general decrease in the number of skin lesions (P<0.05). More entire males mountedtheir penmates than castrates, regardless of their age (P<0.05). Regarding entire males, the amount of mounting was higher inenriched housing at 4 months of age (P<0.05). Thus, environmental enrichment led to a decrease in skin lesions that wasfavourable to the welfare of pigs but the sexual development and aggressiveness of entire male pigs was weakly modified.