Fifty-four Hereford calves (31 males, 23 females) were used in a randomized block design (2 spatial replications) to evaluate the effect of herbage allowance of grasslands during their fetal and early life (130 d of gestation to weaning) on calf BW and body composition during the first year of age. Their dams (primiparous, 5.9 ± 0.5 BCS 1–8 scale, 472 ± 35 kg BW) were allocated in a factorial arrangement of prepartum (fall, 130 ± 12 d of gestation to calving; high vs. low, PREH vs. PREL) and postpartum (spring-summer, birth to weaning; high vs. low, POSTH vs. POSTL) herbage allowance (4 vs. 2.5 kgDM/kgBW of annual mean). Males were castrated at birth. Calf BW was determined at birth and monthly thereafter until the first year of age (390 ± 12 d). Body composition was determined at 200 (weaning) and 390 d using the urea dilution technique. Means from a mixed model repeated analysis were considered to differ when P ≤ 0.05. Calf birth weight was not affected by PRE and was greater in male than female calves (33.7 vs. 32.5 ± 0.2 kg). Calf BW at 200 and 390 d or pre and postweaning average daily gains (ADG) were not affected by PRE but calf BW at 200 and 390 d was 30 ± 3 kg greater in POSTH than POSTL calves due to a greater preweaning ADG (+152 ± 0.02 g/d). Carcass fat increased (10.7 vs. 14.2 ± 1.2%) while water (62.4 vs. 60.1 ± 0.7%) and protein (19.1 vs. 18.3 ± 0.3%) decreased from 200 to 390 d. Body composition was affected by the interaction between PRE and POST as carcass fat was greater while water and protein percentages were less in PREL-POSTH than PREL-POSTL calves, being intermediate in PREH-POSTL and PREH-POSTH calves (10.3, 15.2, 12.2 and 12.6 ± 1.2% for fat, 62.7, 59.6, 61.6 and 61.0 ± 0.7% for water and 19.2, 18.2, 18.8 and 18.8 ± 0.3% for protein for PREL-POSTL, PREL-POSTH, POSTH-PREL, and POSTH-POSTH, respectively). Improve forage allowance during calf lactation period modified body composition of calves born from cows grazing low herbage allowance during gestation, as the increase in calf BW was associated with increased fat in detriment of protein deposition.