Metabolisable energy can be predicted from nutrient composition data and in vitro digestibility, using equations.

Attached an article for details.

Gross Energy includes all the energy in a feed. It is not all available to the animal. It is determined by how much heat is liberated upon combustion.

Digestible Energy (DE): Portion of gross energy that is digested. It is how much energy does not end up in the feces. Therefore, it was absorbed. It is not all used by the animal, some is lost.

Metabolizable Energy (ME): Portion of gross energy that is useful for metabolism. It is what is left after accounting for energy in feces, urine and gasses. It is still not all available for the animal to use.

Net Energy (NetE): Portion of metabolizable energy that is useful for maintenance and productive functions.

Calculations:

1 calorie = energy to raise 1 g H2O 1° C

1000 cal = 1 Kcal

(In humans 1 Calorie = 1 Kcal, animal nutritionists don’t ause Calorie vs calorie)

Temp rise X g H2O = clories in sample

Cal in sample X amount of feed = Cal in feed, same for feces.

Calculate the total calories (or Kcal) (per day) eaten and excreted (in feces, urine).

Calculate DE, ME, Net E (must know the endogenous contribution in Kcal/Kg and %

For Kcal/Kg divide the Kcal of interest by Kg consumed

For %, divide the Kcal of interest by Kcal of feed consumed (times 100).

Here is an older publication that shows ME for many broiler feeds. Although it is 21 years old, it is still useful information for hundreds of feeds.

My basic message would be: digestibility of the nutrients (energy) in the intestinal tract and subsequently the efficiency of conversion of these (absorbed) nutrients into energy used by the body determines what part of the Gross Energy (combustion value) is used by the animal (Metabolizable Energy). 

Thus digestibility and efficiency of utilization are key factors and can not always be predicted from existing data.

Usually there is equations used for calculation of ME in poultry depending on the nutrient composition of the feedstuff or the final diet

The nutrient considered are (Moisture, Protein, Fat, Fiber, Starch and Sugar)

Each equation considered some of those nutrients

So you find different results     

Multiply the gross energy by 0.82. Research has shown that the feacal and urinary energy loss in poultry is 18%, hence, metabolizeable energy in poultry is 82% of the Gross energy.

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