PERTANIKA JOURNAL OF TROPICAL AGRICULTURAL SCIENCE

High-quality lean tissue growth, feed efficiency, and proper immune function are essential for broiler production. Maize and soybean meal remain major ingredients in commercial broiler feeds, but their amino acid composition often does not match the dietary need for methionine (Met), lysine (Lys), and tryptophan (Trp), especially when crude protein (CP) content is lowered to improve nitrogen efficiency. In this review, the functional roles of Met, Lys, and Trp in broilers are discussed within the context of their practical applications in feed supplementation, low-CP formulation, and long-term feed crop improvement. Met is crucial for protein synthesis, methylation, antioxidant activity, and immune function. Lys plays a critical role in muscle growth, carcass development, and shaping the ideal protein profile. Trp is involved in appetite regulation, serotonin and melatonin synthesis, stress response, and immune function. This review also addresses how the amino acid content of maize, soybean, and rice can be improved through biofortification and gene editing. It highlights that amino acid optimisation should be based on an integrated approach rather than individual nutrient additions. In the short term, the focus should be on balanced digestible amino acid provision and crystalline amino acid use. In the long term, crop biofortification should consider agronomy, nutritional value, economics, regulation, and consumer acceptance. Future studies should combine controlled broiler feeding trials with metabolomics, transcriptomics, microbiome, and proteomics approaches to evaluate tissue metabolism, gut health, nitrogen efficiency, and meat quality.