Low-protein diets for broilers: Current knowledge and potential strategies to improve performance and health, and to reduce environmental impact

Amino acids (AA) are the second most expensive component of broiler diets after energy, and therefore their excessive inclusion in diets can result in significant increase in broiler feed cost. In addition to the increased feed cost, excessive intake of AA by broilers results in increased N excretion, which has negative impact on environment, and welfare of birds and caretakers. Also, excessive intake of AA by broilers results in increased excretion of water and hence increased litter moisture, which has negative impact on environment and welfare of birds. Finally, excessive intake of AA can result in increased production of toxic compounds in hindgut from AA post small intestinal digestion. Thus, methods to reduce dietary CP level without compromising performance of broilers will reduce feed costs and improve the environment, and may improve poultry health and welfare. The dietary level of CP can be reduced without compromising performance of broilers if the resulting low-CP diets are supplemented with crystalline AA to meet the AA requirements of broilers. By supplementing the diets with crystalline AA, the CP values in broiler starter, in this paper any period between hatch and approximately days 21 of age and finisher, in this paper any period between day 21 and day 42 of age, diets can be reduced from approximately 220 and 200 g/kg to 190 and 170 g/kg, respectively, without compromising growth performance of the broilers provided the digestible Lys, Met, Thr, and Val contents in low-CP diets are similar to those in the high-CP diets. The level of CP in broiler starter and finisher diets can be further reduced to 180 g/kg and 160 g/kg, respectively, without compromising growth performance of the broilers if the low-CP diets in addition are supplemented by Gly and the digestible content of Lys, Met, Thr and Val, and Gly are equivalent of the low-CP diets to those in the high-CP diets. Publications delineated in this text indicate several strategies to consider for reducing CP in broiler diets including: feed enzymes, soybean isoflavones, fatty acid type, and fiber type. All these strategies are discussed and gaps in knowledge are identified. •Crude protein level in broiler diets can be reduced by 30 g/kg if indispensable AA are added in diets.•Crude protein level in broiler diets may be further reduced by 10 g/kg by adding Gly in the diets.•Crude protein level in broiler diets may be further reduced by 10 g/kg by adding phytase in the diets.•Crude prote