Fats are important energy-yielding raw materials in diets for poultry. It is well known however that they are extremely variable commodities, with factors such as chain length and degree of saturation of constituent fatty acids together with the proportion of free fatty acids having significant effects on fat dietary energy values. A further factor which may affect their utilisation is the age of the bird to which they are fed together with the rate of inclusion. Quantifying this effect would not, however, appear to have been studied in detail. The objective of the current study was an investigation into the interactions between age of bird, fat chemical structure and rate of Inclusion of fat on apparent metabolisable energy (AME) values.