Fouty-8 animals with initial body weight (BW) of 380.2 ± 4.73 kg were used to determine energy requirements of Nellore and Angus young bulls using comparative slaughter technique. Four animals of each breed were slaughtered at beginning of the experiment (baseline animals). The remainder were housed in individual stalls. Eight animals of each breed were fed ad libitum with a whole shell corn (WSC) diet (85% WCS and 15% of a pellet based on soybean meal) or a silage/concentrate (SC) diet (30% silage and 70% concentrate based on corn and soybean meal). Other 4 animals of each breed were fed with the SC diet at 50% of feed restriction, based on dry matter intake adjusted for metabolic BW of animals that received the SC diet ad libitum. We measured the daily intake and a metabolic trial was conducted with total collection of feces and urine to estimate the metabolizable energy intake (MEI). At 90 d of growth, the bulls were slaughtered. Heat production (HP) was calculated as the difference between MEI and retained energy (RE). The net energy requirements for maintenance (NE_m) was estimated considering the intercept of the equation HP = a × e^{(b × MEI)}. The metabolizable energy requirements for maintenance (ME_m) was calculated by iteration, assuming the value which HP and MEI are the same. The efficiency of ME utilization for maintenance (k_m) was obtained as the NE_m divided by the ME_m. The slope of the regression of RE on MEI was assumed to be the efficiency of energy utilization for growth (k_g). The data were analyzed using the GLM and NLIN procedures of SAS adopting significance level of 0.05. NE_m was different between Angus and Nellore (99.8 vs 75.8 kcal/kg EBW^0.75/d). The ME_m was 150 and 122 kcal/ kg EBW^0.75 and the k_m was 67 and 62% for Angus and Nellore cattle, respectively. We did not find difference between breeds (P > 0.05) in k_g (20%).