SUMMARY: L-tryptophan is a biosynthetic precursor for the neurotransmitter serotonin. It has been hypothesized that decreased concentrations of this amino acid would lead to reduced formation of serotonin and possibly more aggressive responses to stimuli in dogs. Three groups of dogs with dominance aggression, territorial aggression, and hyperactivity respectively were fed diets differing in protein and tryptophan levels. It was found that, for dogs with dominance aggression, adding tryptophan to a high-protein diet or changing to a low-protein diet may reduce aggression. For dogs with territorial aggression, a low-protein diet with added tryptophan may be helpful in reducing aggression. The behavior of hyperactive dogs was not influenced by dietary protein content or addition of tryptophan.
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