I am not sure if I am able to answer your question, but I will
give it a try and hope that someone tells us if I'm wrong.
Biologists talk about different kinds of energy depending on
where you measure it. The first measurement is the gross energy
(GE) which is measured through bomb calorimetry and is basically
how much heat a substance gives off when completely burnt. I
have recently read in a compendium that the GE value of fat is
~9,4 kcal/g. The next stage is digestible energy (DE), which is
how much of the forage you actually can digest, which would
exclude for example fibres. Next stage is the metabolizable
energy (ME), the energy which can be used in actual metabolism
(DE - energy losses from transporting nutrients etc). This are
the value you reported. (I don't have a source, but I've heard
the same values from multiple recognized sources.) Now is the
part where it gets a bit trickier, as the final measurement of
energy is the net energy (NE). This is defined as the metabolic
energy minus the heat incr