Aggressiveness and productive performance of piglets supplemented with tryptophan.

Early weaning is a common practice in pig farms, this might cause distress and fighting among piglets. The amino acid tryptophan is the precursor of the neurotransmitter serotonin, which has sedative effects that reduce aggression, however, it also has anorexigenic effects that could reduce feed intake and weight gain. In this study, it was evaluated tryptophan supplementation above requirement levels in social behaviour and productive performance of piglets weaned at 21 days of age. Four levels of dietary tryptophan were used (T , 0.23%, Control; T , 0.27%; T , 0.31% and T , 0.35%). Tryptophan was orally supplemented to each piglet 1 2 3 4 every day. Treatments were randomly assigned to 544 piglets (5.69±1.14 kg) with 8 replicates per treatment. Behavioural observations of piglet activity were done for 6 h daily during four consecutive months, in periods of 8 days, from 14-2 h. Data were analyzed with PROC MIXED according to a completely randomized design with repeated measurements. Aggressiveness measured as biting appendixes (ears and tail) and fighting, were different among treatments (p 0.05) were found for feed intake, daily weight gain and feed conversion between treatments. Results showed that tryptophan supplementation reduced aggression in weaned piglets, however, there was no change in productive performance.