The updated requirements and functional roles of dietary protein and amino acids in ducks: a comprehensive review

Waterfowl, primarily ducks, constitute a major commercial poultry species globally, their production efficiency is heavily influenced by dietary protein and amino acid intake. Although the National Research Council (NRC, Nutrient requirements of poultry, 1994) established fundamental recommendations for protein and amino acid requirements in ducks, tremendous improvements and changes (growth speed, rearing system, and dietary strategy) have been made in duck industry over the past decades. Consequently, these standards no longer adequately reflect the nutritional needs of modern duck production systems. This review presents updated estimates of dietary crude protein and key amino acid requirements, including methionine, lysine, threonine, tryptophan, and arginine, etc., which are essential for formulating precision diets to maximize growth performance, carcass yield in meat ducks, as well as reproductive performance in laying ducks and breeders. Furthermore, the functional roles of these amino acids as critical regulators of physiological processes are systematically examined, including lipid metabolism (methionine and threonine), intestinal barrier integrity (threonine), regulation of feed intake via nitric oxide (arginine), and the modulation of behavior and stress responses (tryptophan). The implementation of low-protein dietary strategies (crude protein levels as low as 15% for growing meat ducks, and 14.5% for laying ducks) is also discussed for maintaining performance while improving nitrogen utilization efficiency. The recent publication of updated Chinese national feeding standards for meat-type (GB/T 45103-2024) and laying ducks (GB/T 41189-2021) incorporates these modern research advances, representing a significant milestone and providing a modern framework to guide the global duck industries. In summary, this review highlights the urgent need to move beyond outdated nutritional standards and adopt modern, evidence-based amino acid requirements tailored to modern duck production. The integration of low-protein diet strategies along with a refined understanding of amino acid functions is crucial for optimizing duck production, enhancing nutrient efficiency, and reducing environmental impacts. Future research should focus on establishing the precise requirements for other essential amino acids and certain non-essential amino acids, and further elucidating how amino acids molecularly modulate gene expression, signaling pathways, and gut microbiota to develop innovative and sustainable nutritional strategies for ducks.