Individual variation in pigs is well known, although poorly understood and is often overlooked. This thesis investigates the differences in individual pig performance, energy expenditure and macronutrient oxidation in growing pigs and how those indices are related to behavioural responses to stress. Behavioural responses of 19 female Yorkshire pigs during 4 behavioural tests conducted at weaning were compared with performance variables, energy expenditure and macronutrient oxidation from weaning to finishing and carcass composition at slaughter. The data suggests that exploratory behaviour expressed during the Human Approach Test at weaning, can be indicative of the animal’s performance potential through to market weight. In the present study, increased exploratory behaviour was associated with advantages in average daily gain, gain to feed ratio and carcass fat content. This could be of great benefit to the pork industry as it could allow producers to select for more productive animals with the use of a simple and non-invasive behavioural tests while improving animal welfare. However further studies are warranted to more clearly understand the mechanisms behind these relationships.