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Application of L-tryptophan in pig feed

Trp is the fourth limiting amino acid in piglet diets after lysine, threonine, and methionine, and has become the second limiting amino acid in low protein corn soybean meal diets. Tryptophan belongs to the non polar aromatic amino acid group and contains a special indole group. Due to this structural specificity, its metabolic pathway is more complex than other essential amino acids, resulting in multiple functions in the body. It not only participates in the synthesis of proteins in the body, but also its metabolites participate in various nutritional and physiological metabolic functions such as immune regulation and food intake regulation.
L-tryptophan is an essential amino acid in animals, involved in protein synthesis and metabolic regulation. It is also a precursor of serotonin (HT), melatonin, tryptamine, nicotinamide adenine dinucleotide (NAD), niacin, and other metabolites. These metabolites have broad physiological effects in animals:
1. Regulating protein synthesis
L-tryptophan participates in the regulation of protein synthesis, and its promotion of liver nucleoprotein synthesis is related to the binding ability of L-tryptophan to special nucleic acid tryptophan receptors after its distribution in vivo.
2. Immune and digestive functions
Tryptophan can produce melatonin, which is a pineal gland hormone and therefore has an impact on animal immune function. L-tryptophan can also promote the differentiation of bone marrow T lymphocyte precursors into mature T lymphocytes, and L-tryptophan deficiency can lead to a decrease in humoral immune function. L-tryptophan can also promote the production of gastric and pancreatic juices, promoting the digestive function of animals.
3. Nutritional Metabolism
Tryptophan can be changed into 5-hydroxytryptamine and nicotinic acid after oxidative decarboxylation in the body. 5-hydroxytryptamine, as a neurotransmitter in the central nervous system, has functions such as antidepressant, sleep promoting, analgesic, and antihypertensive, all of which are related to its antipsychotic effect. In the peripheral system, serotonin can cause microvascular contraction and increase blood pressure, and also serves as a neurotransmitter. Animals can feed on the central nervous system by synthesizing 5-hydroxytryptamine from L-tryptophan in the diet, thus improving their appetite. Oral administration of tryptophan can increase feed intake and increase the expression of the gastrointestinal regulatory peptide Chrelin in piglets.
4. Adjusting feeding intake
Tryptophan is a precursor of the neurotransmitter serotonin (5-HT) in the brain, which acts on the feeding center of the hypothalamus and regulates animal feed intake. High levels of tryptophan in the diet can increase the lying time of pigs and reduce feeding time. Adding tryptophan can improve the aggressive behavior of pigs to a certain extent, thereby reducing their energy consumption, increasing their daily weight gain and feed reward.
Demand
NRC (1998) recommended that the total tryptophan requirements for piglets weighing 3-5 kg, 5-10 kg, and 10-20 kg be 0.24%, 0.22%, and 0.18%, respectively.
Reference: Wang Jiqiang, Zhang Baotong, Long Qiang, Li Aiqin, Physiological function of tryptophan and its application in piglet diets [J], Hunan Feed, 2012, 4:25-27.