Effects of injections of bovine somatotropin (bST) to suckling beef heifers on pre- and post-weaning growth performance and puberty achievement. Angus × Brangus heifers (n = 30; BW = 140 ± 20 kg; age = 132 ± 15 d) were stratified by BW and age, and randomly assigned to receive s.c. injections of saline (SAL; 5 mL; 0.9% saline) or half-dose of bST (250 mg of sometribove zinc; Posilac, Elanco, Greenfield, IN) on d 0, 14 and 28 (15 heifers/treatment). Then, cow-calf pairs were grazed on 4 bahiagrass pastures (7 to 8 pairs/pasture) from d 0 until weaning (d 126). Unshrunk BW and blood samples were collected on d 0, 14, 28 and 126. From d 126 to 350, heifers were grazed on bahiagrass pastures (1 pasture/treatment) and fed blackstap molasses-based concentrate at 1.1% BW (DM basis). Unshrunk post-weaning BW was obtained every 28 d, and blood samples every 10 d to determine plasma progesterone (P4) concentrations. Heifers were considered pubertal when 2 consecutive plasma samples had P4 ≥ 1.5 ng/mL. During the pre-weaning phase, bST injections increased ADG from d 0 to 42 (1.2 vs. 1.1 ± 0.04 kg/d; P = 0.03), but not ADG from d 42 to 126 or weaning BW (0.89 vs. 0.84 ± 0.028 kg/d and 266 vs. 261 ± 7 kg; P ≥ 0.28). Also, bST injections increased pre-weaning mean plasma IGF-1 (97 vs. 85 ± 3.7 ng/mL; P = 0.02), and tended to decrease plasma leptin on d 42 (5.2 vs. 5.9 ± 0.24 ng/mL; P = 0.06). Pre-weaning bST injections increased post-weaning mean ADG and BW on d 350 (0.30 vs. 0.22 ± 0.02 kg/d and 329 vs. 311 ± 3 kg; P < 0.01), tended to increase overall puberty achievement (49 vs. 30 ± 6.9% of total heifers; P = 0.06) and decrease age at puberty (402 vs. 435 ± 13 d; P = 0.08), but did not affect BW at puberty (287 vs. 288 ± 7 kg; P = 0.95). Hence, 3 half-dose injections of bST administered to suckling beef heifers at 14-d intervals, between 132 and 160 d of age, did not affect body weight at weaning or puberty, but enhanced post-weaning ADG, tended to increase puberty attainment and decrease age at puberty.