The objective of this thesis was to study the effect of low and high sanitary conditions on amino acids and energy metabolism in pigs. Also interactions between the immune system, nutrient metabolism and damaging behaviour of pigs were considered. The results of this thesis indicate that both energy and amino acid requirements are greater in low sanitary condition pigs compared with high sanitary condition pigs. It is questionable, however, whether it is nutrient and cost effective, and biologically possible to satisfy these increased nutrient requirements in low sanitary condition pigs, as efficiency is low and feed intake is reduced of low compared with high sanitary condition pigs. Also the present thesis demonstrates that care should be taken in reducing dietary protein concentrations to improve protein efficiency in pigs, as it incurs a risk to increased damaging behaviours, particularly for low sanitary condition pigs.