Reduction of potential environmental pollutants is a major issue for the sustainable development of the poultry industry. Accumulation of excessive manure and nitrogen poses a risk to animal and human health and ground and surface water cleanliness. In conventional poultry, synthetic amino acids and enzyme supplementations are commonly used to balance the diet and improve digestibility of nutritive compounds. However, diet preparation with sufficient nutrients and minimum amount of excessive nitrogen which still provides optimal growth and health performance continues to be a challenge. This review focuses on various approaches leading to improvement of feed formulation in conventional poultry production systems. The use of crystalline amino acids and genetically engineered plant protein sources in the conventional poultry industry with regard to optimisation of nitrogen level in poultry diets are discussed, and the application of the ideal protein ratio concept in poultry feed preparation as a tool for nitrogen level optimisation is outlined.
