Abstract Low protein (LP) diets may increase the occurrence of damaging behaviours, like tail biting, in pigs. We investigated the effect of supplementing a LP diet with indispensable amino acids (IAA) or environmental enrichment on tail biting. Undocked pigs (n = 48 groups of 12) received either a normal protein diet (NP), a LP, LP with supplemented IAA (LP + ), or LP diet with extra environmental enrichment (LP-E + ) during the starter, grower, and finisher phase. Performance, activity, behaviour, and body damage were recorded. LP and LP-E + had a lower feed intake, growth, and gain-to-feed ratio, and were more active than NP and LP + pigs. LP-E + pigs interacted most often with enrichment materials, followed by LP, LP + , and NP pigs. LP pigs showed more tail biting than all other groups during the starter phase and the finisher phase (tendency) compared to NP and LP + pigs. Thus, LP-E + only reduced tail biting in the starter phase, whereas LP + tended to do so throughout. Tail damage was more severe in LP pigs than in NP and LP + , with LP-E + in between. In conclusion, IAA supplementation was more effective than extra environmental enrichment in countering the negative effects of a low protein diet on tail biting in pigs.