[Frontiers in Bioscience S3, 286-297, January 1, 2011]

Tryptophan metabolism in animals: important roles in nutrition and health Yu-long Yin1, Ze-Meng Feng 1,4, Zhi-Ru Tang1, Guoyao Wu1,3,5

1Hunan Engineering and Research Center of Animal and Poultry Science and Key Laboratory for Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Hunan, China 410125,2College of Bioscience and Biotechnology, Hunan Agricultural University, Changsha, China 410125,3Department of Animal Science, Texas A&M University, College Station, TX, USA 77843-2471,4Graduate School of the Chinese Academy of Sciences, Beijing 100039, China, 5State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China 100193


1. Abstract
2. Introduction
3. Metabolism and nutrition of tryptophan in animals
3.1. Pathways of tryptophan metabolism
3.2. Tryptophan metabolites
3.3. Tryptophan and immunity
3.4. Tryptophan and neurological function
3.5. Dietary requirements of tryptophan
3.6. Safety of oral tryptophan and its metabolites
4. Summary and perspectives
5. Acknowledgements
6. References


L-Tryptophan is a nutritionally essential amino acid for monogastric animals and preweaning ruminants because it cannot be synthesized in the body. Besides serving as a building block for proteins, tryptophan is a critical nutrient for the functions of nervous and immune systems. Over the past decades, much attention has been directed to study the role of tryptophan as a limiting amino acid in mammalian and avian nutrition. However, emerging evidence from recent studies shows that tryptophan and its metabolites (e.g., serotonin (5-hydroxytryptamine, 5-HT) and melatonin)) can regulate feed intake, reproduction, immunity, neurological function, and anti-stress responses. Additionally, tryptophan may modulate gene expression and nutrient metabolism to impact whole-body homeostasis in organisms. Thus, adequate intake of this amino acid from the diet is crucial for growth, development, and health of animals and humans.