Diets formulated with feed of different ruminal degradation rates can affect the performance and feed efficiency of lambs. In that condition is expected that the carcass weight and its cuts are also influenced changing the potential income for farmers. This work was carried out to evaluate the weights and yield of carcass cuttings of feedlot lambs fed diets of different carbohydrate (CHO) and non-protein nitrogen (NPN) sources. It was used 20 non-castrated crossbred lambs with 4 mo of age and 26 kg of body weight. The diets were composed by 57% of grass hay (Brachiaria hybrid) and 43% of concentrate. The hay was harvested at late mature stage with high (72.4%) neutral detergent fiber and low (4.9%) crude protein. Four concentrate feeds were formulated from the combination of 2 CHO (ground corn: starch; whey permeate: lactose) and 2 NPN (fast and slow release urea) sources. The diets were isoenergetic (2.32 Mcal/kg ME) and isoproteic (11% CP). The lambs were slaughtered at the end of trial after 45 d with a mean body weight of 30.4 ± 1.0 kg. After cooling, the left half of carcasses was separated into 6 commercial cuts of meat: neck, breast, ribs, shoulder, loin and leg. It was recorded the weight of each cut and its proportion in relation to the half carcass. A completely randomized design was used with 4 treatments and 5 replicates. Data were analyzed by ANOVA following a 2 × 2 factorial scheme between CHO and NPN. The weights of neck (0.57 ± 0.02 kg), breast (0.63 ± 0.02 kg), ribs (0.85 ± 0.03 kg), shoulder (1.19 ± 0.04 kg), loin (0.64 ± 0.02 kg) and leg (2.05 ± 0.07 kg) were not influenced (P > 0.05) by the treatments. The same pattern was found to the yield of neck (9.7 ± 0.2%) breast (10.6 ± 0.3%), ribs (14.3 ± 0.2%), shoulder (20.1 ± 0.2%), loin (10.8 ± 0.2%) and leg (34.6 ± 0.3%). The association of CHO and NPN with concentrates of closest degradation rates (whey permeate + fast release urea; ground corn + slow release urea) do not increase (P > 0.05) the weight neither change the yield of cuts of meat in the lamb carcass when low quality forage is added to the diet during the finishing.