Protein efficiency is the ratio between the mass of protein ingested and the mass of protein in the carcass. It is directly related to the environmental impact of pig farming. A higher protein efficiency would reduce this impact by diminishing the excretion of nitrogen compounds and thus the necessary amount of amino acids in the feed while maintaining optimal growth. However, potentially consequences of the selection for increased protein efficiency on the welfare of pigs are so far unknown. It has been shown that pig selected for increased lean mass perform more tail-biting behaviours (Breuer et al., 2005). Potentially damaging behaviours that could affect animal welfare negatively such as biting have a multifactorial origin. Environment, enrichment, nutrition and performance traits are key components on this subject. The behaviours such as exploration and rooting are desirable but need an adequate environmental enrichment, such as straw bedding, to help prevent pigs from redirecting potentially damaging behaviours onto conspecifics (Petersen et al., 1995; Beattie et al., 2000). Striking a balance between animal welfare, environmental benefits and economic efficiency is the main objective. The aim of this work was to observe potentially damaging as well as rooting behaviours in pigs under protein restriction in a straw-enriched environment and analyse the possible effects of protein efficiency on those behaviours.