Introduction: Different sources of roughage and nutritional strategies (additives and processing) can alter the metabolism of animals. Objective: We wished to evaluate the protein metabolism of sheep fed with corn silage or extruded roughage of different fiber levels. Materials and Methods: The experiment was conducted at the Small Ruminants Sector of the Federal University of Uberlândia, Minas Gerais, Brazil. Twenty Santa Inês sheep were used, with an average body weight of 64 kg and an average age of 4 years old, and allocated into metabolic cages. The animals wwere distributed in a randomized design and fed ad libitum with (1) corn silage, (2) 52.5% Foragge® extruded roughage (including virginiamycin as an additive), and (3) 60%, (4) 65%, and (5) 70% Urochloa (with no additives added) at 8:00 am and 4:00 pm during five experimental periods of 15 days (with 10 days of adaptation and 5 days of collection). Blood samples were collected before feeding via venipuncture of the jugular vein using Vacutainer® tubes on days 11, 13, and 15 of the experimental periods. The data were subjected to normality and homoscedasticity tests, followed by an analysis of variance, contrasting for the (1) roughage source and (2) additive addition in the extruded roughage, and regression for the levels of extruded roughage (P≤0.05). Results: No effect of roughage on creatinine (0.82 mg dL⁻¹; P=0.52) and total protein (5.54 g dL⁻¹; P=0.26) was observed. However, there was a significant effect of the roughage source on urea levels (26.06 vs. 35.87 mg dL⁻¹, silage and forages, respectively; P=0.02), albumin (3.07 vs. 3.51 g dL⁻¹; P=0.04), and uric acid (0.29 vs. 0.13 mg dL⁻¹; P=0.01). Additive and the levels of extruded roughage (60; 65 and 70%) did not affect their blood metabolites. Conclusion: The use of extruded roughage results in higher plasma urea, albumin, and uric acid levels compared to those with corn silage, indicating differences in protein metabolism between these two roughage sources.