On the basis of an analysis of energy metabolism measurements on adult cattle (oxen), fed on 110 rations with very heterogeneous nutrient composition, the following prediction equations for gross energy (y1), digestible (y2) and metabolizable energy (y3) as well as for energy deposition effect of rations (y) (kJ) are presented: y1 = 23.6z1 + 34.0z2 + 17.3z3 + 16.0z4 + 19.1z5 y2 = 23.6x1 + 34.0x2 + 17.3x3 + 16.0x4 + 18.0x5 y3 = 17.3x1 + 34.0x2 + 15.9x3 + 15.1x4 + 15.4x5 y = (6.5x + 26.6x2 + 10.1x3 + 7.5x4 + 8.9x5) (-0.5574 + 0.04050x6 - 0.0002633x6(2)) [table: see text]