A cautionary note regarding the use of nutritional L-tryptophan to alter aversion-related behaviour in mice

Nutritional L-tryptophan is reported to have positive effects on the behaviour of several farm animals. The present experiment describes some effects of nutritional L-tryptophan on the aversion-related behaviour of male mice selected for high litter size. The behavioural effects of L-tryptophan were observed in the elevated plus-maze, the light/dark test and a resident-intruder test. The only significant effect was observed in the resident-intruder test, where the total occurrence of exploratory behaviour by the intruder was reduced by L-tryptophan treatment. The present experiment provides a cautionary note advising against supplementation with L-tryptophan to improve animal welfare before the consequences of such treatment are fully understood.