This trial sought to increase the knowledge of the changes in the endocrine status of male sheep as they mature and to link this with their sexual and agonistic behaviour when reared in the presence or absence of females; the influence of female lambs could significantly alter the behaviour, growth, performance, carcass composition and meat quality of entire and castrated male lambs. Therefore, this project could lead to improvements in the efficiency of sheep production by providing the background physiology necessary to understand sexual behaviour. This may lead to improved practices for the management of growing sheep, which may reduce the necessity to routinely castrate all male lambs.