The intake of food is determined by the energy content. This means an animal will eat to satisfy its energy requirements, all other nutritional requirements need to be balanced with energy. The most accurate picture is given by looking at Metabolisable Energy (ME).
Gross-energy is the quantity of heat resolution from the complete oxidation of a substance (Pond et al., 1995). By determining temperature (heat is a form of energy) inside the oxygen bomb calorimeter (IKA calorimeter C4000) before and after burning the sample with pure oxygen, the gross-energy content can be calculated. The ground foodstuff- and faeces samples were weighed before they were ignited with pure oxygen in the oxygen bomb calorimeter. The oxygen bomb calorimeter records the ambient temperature before and after the burning process. With these two temperatures the gross energy content was calculated.
To calculate gross energy content on a DM base, the following formula can be used;
Gross energy(Kj /kg)(DM) = (C x ∆T - QF)/ (Mp x DM of AD)
Were C is the warmth capacity of the calorimeter (J/k); ∆T is the measured temperature rise; QF is the sum of all foreign energies (wire and fibre, (J)); Mp is the weight of the sample (g) and DM of AD is the percentage of DM in the air-dried sample.