The objective of this study was to evaluate the effect of different levels of supplementary protein on the productive performance, ingestive behavior and blood parameters of heifers during the water period. Forty Nellore heifers with initial average live weight of 191 ± 16.65 kg and 13 months of age were used and distributed in a completely randomized design in a rotational grazing system with Magathyrsus maximus. The treatments consisted of four protein levels in the supplement: 0% PB (mineral), 11.4; 18.4 and 27.2 g PB/100 kg PV/day. As the level of supplementation increased the feed protein conversion was worse (p<0.1). The feed conversion of the supplement increase with the highest levels of crude protein in the supplement (p<0.1). The different levels of protein did not influence (p>0.1) the final live weight, average daily gain and total weight gain presenting average values from 257.15 kg, 0.554 kg/day and 65.85 kg, respectively. Was verified the effect of protein supplementation on weight gain per area when evaluated by contrast, (p <0.1), in which protein levels provided an increase in the productivity, 3.4 @/ha during the experimental period. There was no effect (p>0.1) of the protein levels on the variables of glucose, cholesterol, aspartate aminotransferase, alanine aminotransferase, triglycerides, albumin, creatinine, urea and total proteins. The rumination time, leisure time, total chewing time and chewing time were not influenced (p>0.1) by increasing protein levels. There was effect of the protein levels (p=0.064) for the grazing time, which it presented a linear decreasing reducing the grazing time as a function of the increased protein levels. The time to ingest supplements was highest for the animals no protein supplemented (p>0.1), the animals mineral supplemented presenting more chewing number than the animals protein supplemented (p<0.01). When seeking an increase in individual performance of heifers in pasture with good supply and nutritional value of forage, the supplementation with low protein levels and low consumption during the rain season is not indicated. However, is possible to increase the area productivity with the supplementation use. Thus, to choose the appropriate supplementation strategy should be considered the objectives to be achieved within the production system.
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