Eighteen prepubertal Israeli-Holstein heifers were used in an experiment to study the effects of protein supplementation and implantation of Synovex-C on body weight gain (BWG), skeletal size and age at puberty. Heifers were allocated to three treatment groups as follows: 1. heifers received a diet that was formulated according to NRC (1989; Control) recommendations. 2. heifers received the same diet fed to heifers on treatment 1 except that the diet was supplemented with 3.3% maize gluten meal (MGM) during the first 6 months and with 2.5% MGM during the next 3 months 3. heifers received the same diet fed to heifers on treatment 2 and were implanted with Synovex-C. Supplementation of MGM to the diet enhanced BWG during the first 183 d of the experiment. The implantation of Synovex-C enhanced BWG only during the first 92 d of the experiment. From d 93 to 281, BWG of heifers on treatment 3 was reduced, and, by the end of the experiment, the BW of these heifers tended to be lower than of heifers on treatment 2. Supplementation of MGM to the diet enhanced growth rates of the wither and hip during the first 281 of the experiment. However, implantation of Synovex-C eliminated the effect of supplemented MGM, and, towards the end of the experiment, withers and hip heights of heifers on treatment 3 were lower than those of heifers on treatment 1. Implantation of Synovex-C was associated with increased serum IGF-1 during the first 150 d of the experiment and with reduced age and wither height at puberty.