Thirty six zebu steers (35 Gobra and 1 Maure), 2.5 years-old on average, were equally alloted in 3 groups fed different crop by-product based diets. For diets 1 and 2, molassed rice straw and molassed millet straw were offered ad libitum as a basal diet while the other ingredients were mixed and given (2.5 kg/animal/d) as supplement 1 and 2, respectively. In diet 3, all ingredients were mixed and given as a compound feed. The energy content was higher in diet 3 (0.83 FU/kg DM) than in diet 1 and 2 which were isoenergetic, 0.65 and 0.63 FU/kg DM, respectively. Animals were group-fed twice daily (at 08.00 and 16.00 h) during 3.5 months. Diets offered and refusals were daily measured. Cattle were monthly weighed, their body condition was scored using 2 scales of 6 (BCS_0-5) and 9 (BCS_1-9) points, and body lipids and energy were estimated. The level of intake of steers was 101, 94.3, and 148.3 g DM/d/BW^0.75 for the 1^st, 2^nd and 3^rd groups, respectively. Groups 1 and 2 had average daily gain similar (ADG) (446.7 and 425.5 g BW/animal, respectively) and gain in BCS_0-5 (+0.8 points) and in BCS_1-9 (+1.9 points). A spectacular development of the hump was observed in cattle of the 3^rd group which was submitted to the richest diet. They also gained more (P<0.01) weight (AOG : 1012 g BW/animal), BCS_0-5 (+1.9 points) and BCS_1-9 (+3.5 points) than did the others groups. Increased rate of BW gain resulted in an acceleration of body lipids deposits (22.8 kg in the 3^rd group vs 11.5 kg in the 1^st and 11.6 kg in the 2^nd group) and in gain in body net energy (936.6 MJ in the 3^rd group vs 473.9 MJ in the 1^st and 490.3 MJ in the 2^nd groups). Each kg of gain in BW contains on average 264.7 g of lipids and 11.4 MJ of net energy.