Optimisation of dietary energy utilisation for poultry - a literature review

Feed energy is an important production factor in poultry, representing 75% of the total cost of feed. Therefore, maximising energy digestion and utilisation is essential for cost-effectiveness and sustainability in poultry production. Consequently, accurate energy evaluation of raw material and animal requirements for energy is valuable for precision feeding and optimised benefits in growing chickens. Two key strategies to enhance the utilisation of energy from feed ingredients are the use of exogenous enzymes, such as carbohydrases, and accurate energy requirement prediction. Exogenous carbohydrases can enhance nutrient digestion and absorption, especially in diets with viscous ingredients, in which carbohydrases can enhance the digestibility of saturated fat and protein, by 33% and 3%, respectively, and about 4% energy utilisation. This can improve not only energy utilisation, but also gut health by reducing nutrient flow into the hindgut, as the presence of undigested nutrients fuels pathogenic bacteria proliferation. Moreover, accurate energy bioassays are required to provide values of dietary energy and true availability of energy to the birds. Currently, metabolisable energy (ME) systems are commonly used to evaluate poultry energetics. However, ME does not represent the total energy available to the birds, as it cannot measure the proportion of dietary energy that is lost as heat during feed ingestion, absorption and metabolism. In fact, the ME system can underestimate energy provided by fat by 13% and overestimate energy from proteins by 20% in chicken feeds. As net energy (NE)/ME ratio can vary from 59% to 77% depending on dietary composition, the NE systems are suggested as alternative, more accurate energy measurement methods, as they provide energy values corrected for heat increment. This paper reviews energy sources for poultry and addresses the potential to use NE measurements as a tool to evaluate the ability of feeds and feed additives to improve the exploitation of energy utilisation.