The Role of Tryptophan Supplementation in Enhancing Gut Health, Antioxidant Activity, and Reproductive Performance in Broiler and Broiler Breeder Chickens

Abstract

Tryptophan (Trp) is an essential amino acid in broiler nutrition with roles extending beyond protein synthesis. As a precursor for serotonin, melatonin, and niacin, Trp supports gut health by enhancing motility, villus morphology, tight junction integrity, and promoting beneficial microbiota while suppressing pathogens. Its conversion to melatonin improves antioxidant capacity by increasing superoxide dismutase, catalase, and glutathione peroxidase activities, reducing oxidative damage in muscle, and improving meat quality by lowering drip loss and the incidence of pale, soft, and exudative (PSE) meat. Trp also mitigates heat stress by modulating the hypothalamic–pituitary–adrenal axis, reducing circulating stress hormones, and decreasing heat shock protein expression. Through the kynurenine pathway, Trp metabolism enhances immune function by supporting lymphocyte activity, cytokine production, and maintaining intestinal IgA levels even under toxin exposure such as ochratoxin A. However, excessive supplementation may provoke local inflammatory responses, underscoring the need for precise dietary balance. These mechanisms highlight Trp’s multifaceted role as both an essential nutrient and a functional feed additive that can improve growth performance, health, and welfare in modern broiler production systems.