The objectiveof this work was to evaluate effect of based-soybean or cottonseed meal concentraterations in diets with corn silage on nitrogen balance (NB) and microbial proteinproduction in growing dairy females. diets consisted of the combination of twolevels of concentrate ration, 1 or 2 kg, and two protein sources, soybean mealor cottonseed meal. The animals that consumed 2 kg of concentrate ration showedgreater total nitrogen intake, however, there was no significant effect on fecal-N,urine-N and nitrogen balance. The interaction among the concentrade levels andthe protein source affected the urine uric N (N-urine) but did not change thelevels of ureic nitrogen in the plasma. Levels of concentrate and protein sourcesdid not affect concentrations of total purine and allantoin in the urine, thepercentage of allantoin regarded to total purine, the levels of uric acid inthe urine, microbial nitrogen neither the microbial efficiency. The supply of1 or 2 kg of concentrate ration for growing dairy heifers, using soybean mealor cottonseed meal as protein sources does not affect microbial efficiency,although the supply of 2 kg of concentrate ration causes N waste in feces.
