Tryptophan，as a functional essential amino acid，plays important roles in improving growth performance，modulating feed intake and lactation，enhancing anti-oxidative and immune functions，and so on in animals． When used as a dietary additive to a low -protein diet，tryptophan will reduce dietary protein level，but not alter production performance of animals，which results in relieving the current protein deficiency and decreasing the environment pollution caused by the waste of animal production.
Research over the years has found that tryptophan has the following physiological functions in the body:
1) Synthesize protein as a substrate;
2) Increase the feed intake of livestock and poultry;
3) Reduce the stress response of animals;
4) Improve animal growth performance;
5) Reduce liver fat content;
6) Produce hormones;
7) Improve feed utilization rate.
In recent years, it has also been discovered that tryptophan also plays an important role in regulating the immune function of livestock and poultry. Insufficient tryptophan in the diet will reduce the nutritional level and immune function of the animal’s body, and at the same time, the animal’s susceptibility to disease, morbidity and mortality will be greatly increased. Tryptophan, as a restricted amino acid of immune-related proteins, directly regulates the humoral immunity of animals. A large number of animal experiments have proved that tryptophan has a certain effect on the phagocytic ability of macrophages and the proliferation ability of spleen lymphocytes, and tryptophan can inhibit the proliferation and differentiation of T lymphocytes, and may have a certain effect on the immune escape of tumor cells; In addition, the increased tryptophan content in the diet will promote the synthesis of immunoglobulin in the animal’s serum and enhance the body’s immunity. Tryptophan plays an immune regulatory role in different organs and tissues of the body mainly through its metabolites.
Keywords: tryptophan; metabolic pathway; physiological function; livestock and poultry; regulation