Pigs are believed to posses a strong motivation to perform exploratory behaviour, which include a range of activities such as walking, orientation towards stimuli and direct investigation. Under free-ranging conditions these activities often occur in connection with foraging (Stolba and Wood-Gush, 1989). In ad libitum fed young growing pigs the provision of straw has been found to stimulate various behaviours involving direct investigation of the straw (e.g. Fraser et al., 1990; McKinnon et at., 1989). As it is assumed that growing pigs under such ad libitum conditions ingest sufficient nutrients, it is often assumed that the straw directed behaviour is unrelated to feeding motivation. However, individual pigs offered single diets may not be able to meet their nutritional requirements (Kyriazakis et al., 1990), and this may have behavioural consequences. For example, the straw directed behaviour observed in growing pigs may be a reflection of unfulfilled nutritional demands and in fact represent appetetive foraging. The aim of the present experiment was to assess the extent to which the exploratory activity of growing pigs is affected by limitations in nutrient intake (specifically the crude protein content of the food).