A model fittedto grazing females Nellore during the rearing periods of the Cerrado Regionof Central Brazil was simulated and validated in this study. Body weight gain(BWG) was determined during three years as follows: 1) first dry season afterweaning on Brachiaria brizantha (Hochst) Stapf., 2) rainfall season and3) second dry season both on Panicum maximum Jacq. cv. Tanzâniaand averaged 0.020, 0.550, and 0.172 kg, respectively. In the second rainfallseason during the rearing period heifers grazed Brachiaria decumbensStapf. At 24.33 months of age the heifers body weight (BW) averaged 299 kg whilein the beginning of the mating season their age and BW averaged, respectively,25.51 ± 0.99 months (CV = 3.50%) and 309.33 ± 19.19 kg (CV = 6.20%).On average, animals calved 326.71 ± 19.98 days (CV = 6.11) after thebeginning of the mating season and 36.26 months of age. The mean pregnancy ratewas 88.4%. The pregnant heifers were 25.58 ± 9.97 days older and 9.8± 7.04 kg heavier than those non-pregnant. The mean BW and body conditionin the middle of the mating season were 360 ± 31.00 and 2.94 ±0.60, before calving 436 ± 30.86 kg and 4.57 ± 0.40, and at weaning369 ± 33.89 kg and 3.11 ± 0.64, respectively. The mean weaningrate was of 75.6%. Calves mean BW and age at weaning were of 158 ± 20.1kg and 202 ± 16.6 days, respectively. Nellore heifers grazing Brachiariadecumbens Stapf. and bred at 24/26 months of age showed high production.
