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Animal performance declines considerably after summer dormancy during the grazing season in the steppe rangelands of East Anatolia. The aim of this study was to determine the growth performance of Holstein heifers grazed on rangeland and supported with concentrate. Forage amount, crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) contents of forage were sampled biweekly during the grazing season. In the experiment, heifers (250 ± 10 kg) were allocated to 1 of 3 feeding trials: 1) control, 2) grazing plus concentrate supplement fed at 1% of bodyweight once daily, and 3)grazing plus concentrate supplement fed at 1.5% of bodyweight once daily. The forage allowance increased from the beginning to the middle of July and thereafter continuously declined until the end of the season. CP content of forage declined from the beginning to the middle of July and thereafter it slightly increased until the end of the season. Both NDF and ADF content of forage increased from the beginning of August and thereafter declined. Bodyweight increased throughout the season, and the increases were considerably higher in the supplemented groups than in the control. Total live weight gain at the end of the grazing season was higher in the supplemented groups than in the control; however, there were no significant differences between the supplemented groups. According to the study results, concentrate supplement fed at 1% bodyweight after the start of summer dormancy can improve animal performance in the rangelands in this region. [ABSTRACT FROM AUTHOR]