A total of 378 unsexed Anak broiler chicks were used to assess the effects of varying energy levels and manipulation on growth, haematology, and carcass traits. The experiment was conducted in two phases. First, one-day-old chicks were randomly assigned to one of three starter diets, which differed in their energy density (LSE: 2786.80 Kcal/kg; OSE: 3015.40 Kcal/kg; and HSE: 3252.20 Kcal/kg). The chicks were assigned to seven replicates per treatment with 18 chicks per replicate. When the chicks were 27 days old, they were randomly re-allocated to three finisher diets (LFE: 2770.66 Kcal/kg, OFE: 2961.74 Kcal/kg, and HFE: 3150.43 Kcal/kg). Thus, there were seven replicates of nine treatments with six chicks per replicate in the finishing phase. The starter and finisher diets were isonitrogenous. Birds fed the OSE and HSE starter diets gained more weight and were heavier at 27 days than birds fed LSE. Energy intake by birds fed HSE was greater than by birds fed OSE, and birds fed OSE had greater energy intake than birds fed LSE. Feed conversion ratio was improved for birds fed OSE and HSE. Birds fed LSE and then HFE consumed the least feed and gained as much or more weight during the finisher phase as any other group. Overall, FCR between days 27 and 50 tended to differ among the treatments (P =0.06). Total protein intake increased with decreasing dietary energy in both phases. Varying dietary energy levels did not affect the haematological parameters, carcass traits and internal organ weights.