The commercial trend of increasing slaughter weight in finished pigs, combined with the UK practice of using entire boars for production, might have detrimental consequences for behaviour, carcass quality and production efficiency. The associated increase in age is linked to an increased risk of reaching sexual maturity, with endocrine changes that result in behavioural problems and carcass taint. There is limited research examining environmental effects on performance and behaviour of pigs of modern genotypes finished to heavy weights. The sexual behaviour of boars can be influenced by the social environment during rearing (Thomas et al, 1979) suggesting that the risk of adverse behaviour around puberty might be modified. This study explored the effect of contact with the opposite gender on behaviour and performance in entire males and gilts in the 60kg-130kg weight range.