The objective was to evaluate the production and efficiency of 24-month-old Red Angus primiparous cows of different weights at weaning and repetition of pregnancy. Before calving, the females were managed in natural prairies and fed sweet clover (Lotus corniculatus) and ryegrass (Lolium multiflorum Lam.), with loads of 315 and 501 kg ha-1, respectively. Females were divided into groups according to the average birth weight into light 346.15 ± 3.39 kg; moderate 381.95 ± 2.99 kg; and heavy 412.63 ± 3.33 kg weights. The indicators evaluated were: primiparous weights and body conditions at calving and weaning, daily average and total gains, fixed-time artificial insemination (FTAI), and accumulation. Calves at birth and weaning had their daily average and total weights evaluated. In terms of production, the daily average and total gains per pair and effective herd production (EHP) of the weight groups were measured. At weaning, morphometric measures, viz. croup height and thoracic perimeter had a linear relationship increasing with the weight at calving. In FTAI and cumulative pregnancy, the groups of light and moderate cows were more efficient than the heavy group cows, with values of 81.25%, 75.00%, and 55.56%, respectively. The EHP differed between the groups with values of 37.07 ± 1.71, 28.13 ± 1.50, and 19.99 ± 1.68 kg, for light, moderate, and heavy, respectively. Light cows were 31.8% and 85.4% higher in effective production than moderate and heavy cows, respectively. Knowledge of the production system is important for enhancing breeding efficiency. The improvement in productive performance is related to the adequacy of metrices used in the production system.