The effect of dietary treatments on urinary excretion of purine derivatives and microbial nitrogen supply are presented in Table 5. The findings under this investigation revealed significant (p < 0.05) improvement in N balance in terms of N intake, faecal N, urinary N, N absorption and N retention and urinary purine derivatives. As a result of this study, beef cattle fed 50 g/kg urea, 20 g/kg urea + 20 g/kg Ca(OH)2 and 30 g/kg urea + 20 g/kg Ca(OH)2-treated rice straw resulted in higher N retention, microbial protein supply and efficiency of microbial N synthesis (EMNS)when compared with the control group (p < 0.05). However, there were not significant (p > 0.05) differences among treated groups.