Physiological roles of tryptophan in pig nutrition.

Tryptophan (TRP) is shown to play original roles in the physiology of pigs. Dietary TRP deficiency induces depression of the appetite leading to reduced growth performance. Brain hydroxy-indoles, including the neurotransmitter serotonin, are closely related to dietary TRP supply. Excess protein, namely large neutral amino acids (LNAA) enhanced the appetite depression, providing some support to a role for plasma TRP:LNAA in the regulation of protein intake through serotonin. Other implications of TRP, as a precursor for serotonin, in the susceptibility of pigs to stress and in their consequences on meat quality were reported. Furthermore, we concluded to a role for TRP in the insulin response to the meal and in tissue sensitivity to insulin. Implications in pig feeding practice are briefly reviewed.