Some standards provide true metbolizeable energy of diferent ingredients for poultry. Does the formulation on TME bases can fulfill the energy requirements efficiently???
Whether you use true or apparent metabolisable energy system, you always have to know (exactly) the composition and digestibility of the feedstuffs in your diet.
The inaccuracy in that knowledge might well be more important than the apparent or true system, in calculating the nutritional or energy value of the diet.