The objectives of this study were to determine the fermentative characteristics of forage sorghum (FS; Sorghum bicolor) and Sudax (SX; sorghum x sudan hybrid) preserved as haylage in large round bales (LRB), and to compare the voluntary intake (VI) and in vivo digestibility of haylage of the two varieties. For the first objective, samples taken from two LRB of each sorghum variety after four periods of fermentation (3, 7, 14 and 30 d) plus the initial forage (d 0) were analyzed for pH, concentration of organic acids and NH3-N/total N ratio. The data were analyzed in accordance with a completely randomized experimental design with a factorial arrangement of 2 (sorghum varieties; FS and SX) x 5 (days of fermentation) and two replicates per combination. For determination of VI and digestibility of the dry matter (DM), crude protein (CP) and neutral detergent fiber (NDF) fractions, eight creole sheep (randomly allotted to eight cages and to one of two dietary treatments) were used in a trial of 15-d duration: 3 d for adaptation to the physical facilities, 7 d for adaptation to the experimental diet, and 5 d for collection of comparative data. The daily offering of haylage, taken from two bales of each variety, was at the rate of 3% of bodyweight on a dry basis, and water was available ad libitum. The comparative data were submitted to analysis of variance applicable to repeated measures; these were days 1 to 5 of fecal collection. The initial chemical composition (dry basis) of the fresh vegetative material (35 or 36% DM) of both sorghums destined to haylage was similar except for CP percentage (SX = 5.75; SF = 9.05). There were no significant differences between sorghum varieties in pH or in concentration of organic acids (lactic, acetic, propionic and butyric) of the fermented vegetative material nor significant interactions of variety by day of fermentation. Neither variety reached the recommended pH level (less than 5), and some accumulation of ammonia was observed indicating an unstable fermentation. There were significant differences (P = 0.05) in favor of SF over SX in VI of DM, CP and NDF; and in digestibility (%)of DM (SX = 41.92; SF = 64.90) and CP (SX = 47.09; SF = 70.68), but not of NDF. In summary, poor fermentation characteristics were observed in haylage of SF and SX fermented in LRB. Superiority in DM and CP and digestibility indicated greater nutritive value in FS than in SX.