Gross Energy is not a very good predictor of feeding values for poultry. Metabolizable energy is/was preferred. See also attached European Feeding values Table
Good day, you may consider the metabolizable energy, which is more acceptable nowadays rather than gross energy. The metablozable energy (ME) in KCal/kg can be calculated using Pauzenga's formula:
ME (kcal kg-1) = 37xProtein (%)+81.8xFat (%)+35.5xNFE(%)