The objective of this study was to determine the optimum levels of water hyacinth (WH) in cattle rice straw diet by evaluating nutrient and energy intakes, digestibility and economic return. Four local male cattle with average live weight of 214.5 kg were arranged in a Latin square design with four treatments, which included fresh water hyacinth (WH) replacing rice straw at levels of 0, 25, 50 and 75% in the diets (DM basis) corresponding to the WH0, WH25, WH50 and WH75 treatments. The urea-molassesblock was supplemented in all the diets to balance CP intake for the all treatments. The results showed that daily DM, OM and NDF intakes were significantly different (P0.05) among the treatments with a good rumen environment for microbial activities. It was also found that the daily weight gain was significantly different (P

Keywords: water plants, forages, ruminants, rumen parameters, growth