Amino acid supplementation counteracts negative effects of low protein diets on tail biting in pigs more than extra environmental enrichment

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.