Review: Energy partitioning in broiler chickens

Abstract

In commercial nutrition and in research studies, metabolizable energy (ME) is the standard measure of energy used in describing energy requirements and diets for poultry. The provision of dietary energy will influence the intake of all other nutrients. Broilers exhibit an outstanding ability to control their energy intake by adjusting their feed intake as diet energy concentration changes. There is still considerable debate on the accuracy, precision and usefulness of different procedures used for determining ME values of diets and ingredients. ME intake is generally partitioned into energy retained (ER) in body tissues (mainly as fat and protein) and as heat production (HP): ME = HP + ER. There are few reported estimates of HP and its components, fasting heat production (FHP), heat production due to physical activity and the thermic effect of feeding (TEF). Requirements for maintenance (MEm), including major components of FHP and physical activity, are established at around 155 kcal kg BW0.60. We recently reported that maintenance requirements for young broilers based on kg BW0.75 were 8% lower than the values estimated using kg BW0.60, and that BW raised to the exponent 0.60, was a more precise estimator. Gross energy retained in the body as fat (TERF) and protein (TERP), together contribute most of the total energy retained (TER) in the body. Efficiency of ME utilization above maintenance varies from 70 to 84% for lipid deposition in adult birds and between 37 and 85% in growing birds.