The experiment was carried out on 80 Black-and-White Lowland bulls with an average 75% (50.0 to 87.5%) HF blood share and average initial body weight (BW) of 175 ± 5.0 kg fattened to 500 ± 10 kg final BW. The animals were divided into two groups of 40 bulls according to an analogue method based on BW and HF blood share, and fed rations consisting of maize silage and concentrate in an average ratio 64 : 36% in DM for Group N fed according to the net energy system (IZ-INRA, 2001) or 57 : 43% in DM for Group M fed according to the metabolizable energy system (DLG, 1997). Within each group, four subgroups of 10 animals were formed and fattened at a different level of production providing daily BW gains (BWG), g: 800 (subgroup S₁), 1000 (S₂), 1200 (S₃) and 1400 (S₄). The (PDIE-PDIN)/UFV ratio in the ration for Group N was markedly smaller (-1.84 g/UFV) than in group M (+8.52 g/UFV). Daily BWG of animals of Group N in the respective subgroups were 1003, 1169, 1266, 1400 g and of Group M, 1109, 1170, 1308 and 1345 g, but differences in BWG between the parallel subgroups of Groups N and M were statistically insignificant (P>0.05). Performance of animals fed according to both systems, net or metabolizable energy, did not differ markedly, however, formulation of the diet according to the IZ-INRA system compared with the DLG system resulted in superior balancing of energy and protein, as rations formulated according to ME contained markedly more concentrate and less roughage than according to the NE system.