In order to investigate the effects of varying dietary cation - anion balance (DCAB) levels on performance,. diet dry matter digestibility, characteristics of carcass and bone, 24 Holstein male calves with initial live weight of 217.03 ± 56.28 Kg were used. The experimental design was complete randomized blocks with four diets and six groups of calves with equal weights. The diets contained 0, 15, 30 and 45 meq [(Na + Ki - CL/100 gr dry matter. Diets were given as total mixed ration (TMR), ad-libitum for 150 days, to the calves individually Digestibilites were determined using chromic oxide (Cr203). Blood pH and plasma minerals concentration were measured on days 90 and 150. At the end of the experiment blood urea space on the live calves were. measured by injection of urea solution and blood samples were colected after 9, 12 minutes through the jugular vein of the calves, then the calves were slaughtered and carcass cuts, chemical composition of the 9, 10, 11th and 12th boneless ribs and mechanical and chemical characteristics of metacarpus bone were measured. The results indicated that calves fed diet with level of 15 DCAB had the highest average daily weight gain and the best feed efficiency. However differences between diets for average daily dry matter intake and apparent digestibility of nutrients were not significant (P<0.05). Blood pH and plasma Ca concentration were affected by DCA]3 (P <0.05). The differences among means of carcass cuts and chemical composition of the 9. 10, 11 and 12th ribs were not statistically significant. Where as, carcass weight and internal fat to live weight ratio were affected by DCAB (P <0.05). The mineral content of bones were not affected by diets, but Ca concentration was decreased with increasing DCAB (P<0.05). The comparison between mechanical properties of bones indicated that calves fed with 0 DCAB had the highest moment bending (9675 Kg in cm) and strengh (1935 Kg), and differences among the diets for stress and modulus of elasticity of bones were significant (P <0.05). The results of urea dilution tehnique indicated high correlation between urea space and chemical composition and some of carcass cuts, on the basis of this data, urea dilution technique can be used for determination of live body compositions of the Holstein male calves. Generally, the results of this experiment showed that levels of 15 and 30 DCAB improved the fattening performance of the Holstein male calves. This improvement can be due to acid - base balance in the body of the animals.
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