Two trials were conducted for a period of 90 days each to evaluate the feeding value of different proportions of urea treated rice straw and gamba hay in the performance of growing and fattening Yankasa rams. In the first trial, twenty four (24) growing Yankasa rams of mean initial body weight of 15.77Â�2.5 kg and aged 6 - 8 months were allotted to four dietary treatments with six (6) animals per treatment in a Completely Randomized Design. Urea treated rice straw and gamba hay proportions of 0:60, 20:40, 40:20 and 60:0 were used as roughage diets. A concentrate diet consisting of maize grain, cotton seed cake, rice milling waste, wheat bran, bone meal and salt was formulated to contain 15 % crude protein. The animals were fed roughage diets ad libitum while concentrate was fed at 1.5% of individual body weight. Data were collected on growth performance and blood profile. Data generated were subjected to analysis of variance and differences in means were compared using Duncan's Multiple Range Test. The result of chemical analysis showed that treatment of rice straw with urea increased its crude protein content from 3.64 to 8.89 % and decreased the neutral detergent fibre content from 72.16 to 67.98 %. Total dry matter intake varied from 263.11 to 325.01 g/day with the highest value recorded in animals fed 60:0 UTRS:gamba hay diet. Results of crude protein and neutral detergent fibre intake followed similar pattern. The highest (P<0.05) average daily gain (79.81 g/day) was obtained in growing rams fed 60:0 UTRS:gamba hay diet while the lowest (P<0.05) value (44.44 g/day) was obtained in animals fed 0:60 UTRS:gamba hay diet. Growing rams placed on 60:0 UTRS:gamba hay diet had the lowest (P<0.05) feed conversion ratio value (7.77). Dry matter digestibility was significantly (P<0.05) affected by UTRS:gamba hay proportions. Animals fed 60:0 UTRS:gamba hay diet had a high dry matter digestibility (67.62%). The digestibility of other nutrients followed the same pattern. Animals fed 60:0 UTRS:gamba hay diet had significantly (P<0.05) higher nitrogen intake (16.12 g/day) and the lowest (P<0.05) in the diet containing 0:60 UTRS:gamba hay (12.06 g/day). Nitrogen balance significantly (P<0.05) differed across the dietary treatments. Animals fed diet containing 60:0 UTRS:gamba hay had high nitrogen retention (13.30 g/day) while those fed 0:60 UTRS:gamba hay diet had low nitrogen retention (7.78 g/day). With exception of serum creatinine, all the serum parameters measured were significantly (P<0.05) different. Animals on 60:0 UTRS:gamba hay diet had higher (P<0.05) value of serum glucose (61.02 mg/dl) while animals fed 0:60 UTRS:gamba hay diet had the lowest (P<0.05) value (49.55 mg/dl). Serum urea nitrogen and total protein followed similar pattern. In the second trial, twenty (20) intact Yankasa rams with mean initial body weight of 21.87Â�2 kg and aged 12 - 18 months were allotted to four dietary treatments with five (5) animals per treatment in a Completely Randomized Design. Urea treated rice straw and gamba hay proportions of 0:60, 20:40, 40:20 and 60:0 were used as roughage diets. A concentrate diet consisting of ingredients similar to those of the first trial was formulated to contain 13 % crude protein. The animals were fed roughage diet ad libitum while concentrate was fed at 2.0 % of their individual body weight. Data were collected on growth parameters, serum blood profile and rumen liquor metabolites. Data generated were subjected to analysis of variance and differences in means were compared using Duncan's Multiple Range Test. The result of chemical analysis of the experimental diets was similar to that obtained in the growth trial. The result revealed that, there were significant (P<0.05) differences on all the growth parameters measured. Total dry matter intake was significantly (P<0.05) higher (1035.98 g/day) in animals fed diet containing 60:0 UTRS:gamba hay compared to those fed the rest of the diets. Similarly, animals fed 60:0 UTRS:gamba hay diet had high average daily gain (72.89 g/day) compared to animals on other diets. Lowest (P<0.05) value (38.00 g/day) was recorded in animals fed 0:60 UTRS:gamba hay diet. Rams fed 60:0 UTRS:gamba hay diet had the least (P<0.05) feed conversion ratio (14.21) indicating that animals on diet containing 60:0 UTRS:gamba hay were more efficient in converting feed to live weight gain than animals fed other diets. Digestibility of nutrients was significantly (P<0.05) different across the treatment groups. Total nitrogen intake and nitrogen retention were significantly higher (P<0.05) in animals fed diets containing 60:0 and 40:20 UTRS:gamba hay. No significant (P>0.05) difference was observed on rumen fluid pH while significant (P<0.05) differences were obtained on rumen ammonia nitrogen and Total volatile fatty acids (TVFA). Animals fed 60:0 UTRS:gamba hay diet had higher (P<0.05) rumen ammonia nitrogen and TVFA (27.80 mg/dl and 16.13 Mmol/l, respectively). Lowest (P<0.05) values (21.79 mg/dl and 12.98 Mmol/l, respectively) were obtained in rams fed 0:60 UTRS:gamba hay diet. Significant (P<0.05) differences were observed on all blood profile parameters measured except the serum creatinine. The serum glucose, urea nitrogen and total protein values ranged from 50.29 to 61.32 mg/dl, 5.73 to 8.64 mg/dl and 58.77 to 67.03 g/l, respectively. Values obtained for serum glucose, urea nitrogen, serum creatinine and total protein fell within the normal ranges of 50-100 mg/dl, 15-30 mg/dl, 1-2.7 mg/dl and 60-79 g/l, respectively for sheep. In terms of economic benefit, the results revealed that cost of feed consumed per kg body weight gain (497.76 â‚Â�/kg) was lower and better in fattening rams fed diet containing 60:0 urea treated rice straw:gamba hay proportions. The study recommends that urea treated rice straw and gamba hay proportions of 60:0 UTRS:gamba hay could be used to replace gamba hay as sole roughage diet for sheep feeding as sheep had higher weight gain in the treated straw based diets compared to gamba hay based diet. The study further recommends that small-holder farmers may adopt the treatment of rice straw with urea to improve its nutritive value and reduce the cost of feed per kg body weight gain