Abstract The accumulation of subcutaneous adipose deposits occurs in many genotypes of animals adapted to tropical arid conditions. In sheep, good adaptation of fat-tailed sheep breeds, as Rabo Largo, to arid environmental conditions and food shortages can also undergo digestive and metabolic adaptation, including a greater capacity for digestion of poor roughage. Forty lambs (18±3 kg initial BW) were assigned in a randomized completely block design with a 2x2 factorial arrangement of treatments, with 2 breeds – B (Santa Inês- SI and Rabo Largo-RL) and 2 diets – D (low and high energy), resulting in four treatments: SILE, SIHE, RLLE and RLHE. Lambs (20 SI and 20 RL) were individually penned during 43 d and fed 1 of 2 diets with different concentrate: roughage ratio: low energy-LE (with 70% hay and 10.7% CP, DM basis) and high energy-HE (70% concentrate and 12.7% CP, DM basis). At the end of performance period, the intake was recorded and total feces collected for 5 d. Data were analyzed by ANOVA and when a significant effect (P < 0.05) was found, means were compared using Tukey’s method. The G:F ratio had effect only for D (0.12, 0.22, 0.10 and 0.24 for SILE, SIHE, RLLE and RLHE, respectively). There was observed an effect of D and B (P < 0.05) for all variables related to growth and digestibility, with higher means for SI and HE, except for NDF intake (495, 322, 340 and 268 g/d for SILE, SIHE, RLLE and RLHE, respectively) and NDF digestibility (63, 58, 59 and 45% for SILE, SIHE, RLLE and RLHE). It was observed an interaction D x B on CP intake, NDF intake and NDF digestibility. Breed and diets affected the performance and digestibility of lambs. However, RLLE increased the NDF digestibility, but decreased the ADG, suggesting higher fat depots accumulation.