To determine the feeding effect of fresh and water hyacinth silage, a feeding trial was conducted with 25 Pabna growing bulls about 27 months of age and weighing 184.4 kg were divided into five groups on the basis of other initial live weight and then they were randomly assigned to five dietary treatments on body weight, nutrient utilization in bull calves. The dietary treatments are T1 = 100% rice straw +5% molasses; T2 = 100% fresh water hyacinth +5% molasses; T3 = Ensiled water hyacinth (75% water hyacinth +25% rice straw; T4 = Ensiled water hyacinth (50% water hyacinth +25% rice straw); ; T5 = Ensiled water hyacinth (25% water hyacinth +75% rice straw). In all Ensiled water hyacinth 5% water hyacinth molasses was used during ensiling process. In addition to this, 1 kg concentrated mixture per 100 kg live weight was supplied to mall the experimental animals. The study revealed that the average daily DM intake was 7.04, 6.7 and 4.1, 6.4, 6.8 kg for diets T1, T2, T3, T4 and T5 respectively, which did not differ significantly (p<0.01) among the treatment groups. However, DM intake when expressed as percent of live weight or as metabolic body weight showed significant (p<0.01) difference between diets containing ensiled water hyacinth. Daily CP intake was 429.87, 382.69, 307.95, 344.38 and 327.18 g for diets T1, T2, T3, T4 and T5 respectively. The daily average live weight gain in animals fed diets T1, T2, T3, T4 and T5 were 243.3, 226.6, 110.0 and 223.3 g respectively. Live weight gain on diet T4 was significantly (p<0.01) higher than that of diet T1, T2, T3, and T5. The results suggested that ensiled water hyacinth had higher growth response possibly due to better nutrient contents and their utilization. The digestibility of CP was significantly (p<0.01) higher for diets T4 (75.9%), T2 (73.4), T5 (72.9) and T3 (71.8%) compared to that of diet T1 (62.7%). But there was no significant difference between diets T2, T3, T4 and T5 for CP digestibility. The digestibility of Acid detergent fiber (ADF) was 60.6, 40.4, 33.7, 48.9 and 42.2% for diets T1, T2, T3, T4 and T5 respectively. The results revealed that there was significant difference among the diets. Neutral detergent fiber (NDF) digestibility of different diets was significantly (p<0.01) differ among the treatment groups. The ME values were 8.50, 8.52, 8.23, 8.57 and 8.36 MJ/kg for diets T1, T2, T3, T4 and T5 respectively. The daily average nitrogen intake was no significant difference among the treatment groups. But the animals fed on diets T1 showed higher nitrogen intake than the animals fed on T1, T2, T3, T4 and T5 because diets T1 intake more DM than others diet. Besides, N intake was significantly (p<0.01) higher for diet T1 and T4 when compared to the diet T2, T3 and T5 but there was no significant difference between the treatment T1 and T4. The percent N retention did not differ significantly (p<0.01) among the treatment groups although there was a trend to increase in the water hyacinth fed groups. Feed conversion efficiency was significantly (p<0.01) higher in animals fed diets T4 (37.54%). The results of the present study indicated that the supplementation of water hyacinth in straw based diets (T4) resulted in efficient utilization of feed compare to those of the others diet (T1, T2, T3, and T5). Similarly, protein conversion efficiency also showed significant (p<0.01) differences among the dietary groups T1, T2, T3, T4 and T5. Superior protein conversion efficiency was on diets T4 (1.2) followed by T1 (1.76), T2 (1.6), T3 (2.7) and T5 (1.4). Based on chemical composition, nutrient digestibility, nutritive value and animal performance it may be concluded that ensiled water hyacinth can be used as cattle feed in combination with rice straw and feeding of ensiled water hyacinth up to 50% of the roughage DM in straw based diet can be suggested.