The objective of this study was to evaluate the effect of two additives: one of enzymatic nature [Dyadic® Cellulase PLUS (ENZ)] and liquid urea nitrogen (LU) on crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), voluntary intake (VI) and digestibility of treated bluestem grass (BGH; Dichanthium annulatum) hay fed to rams. Nine young rams were used in a 3 x 3 latin square design with the three treatments: BGH without additive (CON), and with added ENZ or LU. The additives were sprinkled over the hay 24 hours prior to being offered daily at the rate of 4% of the animal body weight (BW). Application of ENZ resulted in no important change in VI or digestibility of dry matter (DM), CP, NDF or ADF; but ENZ tended to slightly reduce (P menor 0.11) NDF content (73.91 vs. 74.27%), and increase (P menor 0.09) ADF content (44.37 vs. 42.87%). Treatment of BGH with LU increased (P menor 0.01) the content of CP (8.11 vs. 6.41%), tended to depress (P menor 0.11) that of NDF (73.00 vs. 74.27%) and increase (P menor 0.09) those of ADF (43.17 vs. 42.87%) and lignin (6.30 vs. 5.89%). It also increased VI of CP (87.46 vs. 67.25%) and tended (P menor 0.06) to increase VI of DM (1027 vs. 986 g) and CP digestibility (61.11 vs. 53.98%). Daily VI of DM as a percentage of BW was not significantly affected by the treatments (3.13, 2.94 and 3.23% for CON, ENZ and LU, respectively).