Supplements with different protein sources were evaluated during the transition phase between the rainy and the dry seasons. To evaluate the performance, 20 animals were used with average live weight of 357 kg and approximately 17 months of age, grazing in five paddocks (2 ha), in a completely randomized design, with five treatments and four replications. The supplements were supplied in the amount of 1.0 kg per day. The following treatments were used: FSFT, FTU, FA38, FAFTU and CONTROL. No difference was found (P>0.10) in the daily weight gain. However, the supplemented animals showed 24.3% more in weight gain in relation to the control group. Considering only the supplements (FA38 and FAFTU) that contained cottonseeds meal with 38% CP, the daily weight gain was 0.223 kg/day or 41.8% more than the CONTROL. The nutritional parameters were evaluated in five animals, with initial average weight and age of 249 kg and 17 months respectively, fistulated in the esophagus and in the rumen, distributed in five paddocks of 0.3 hectares each in design of randomized blocks, where each experimental period was treated as a block. No effects were observed to treatments of the protein microbial fluxes and microbial efficiency. There was no effect of the protein sources on the concentration of N-urea in the plasma and the nitrogen’s balance, all being superior to the CONTROL.
