Weight data from birth to 18 months of age of Nelore and Chianina, both meat-producing cattle breeds, were analyzed. Data were corrected for significant effects of environment and utilized to estimate genetic parameters through the non-linear von Bertalanffy model. Average values found for growth parameters in Nelore were: mature weight (A), 312.87 kg; integration constant (B), 0.49; maturity rate (k), 0.13; age at inflection point (T(I)), 3.29 months; weight at inflection point (P(I)), 92.70 kg, and maturity interval (1/k), 8.04 months. For the Chianina animals, the values were 751.38 kg, 0.59, 0.10, 6.64 months, 222.63 kg, and 10.98 months, respectively. Nelore animals exhibited higher maturity rate, smaller maturity intervals, reaching mature weights younger than Chianina animals, although lighter than these at maturity. Heritability estimates presented low values, mainly for mature weight (0.093 and 0.212), age at inflection point (0.062 and 0.202), weight at inflection point (0.093 and 0.212) and maturity interval (0.057 and 0.309) (for Nelore and Chianina, respectively). The parameters mature weight and weight at inflection point presented positive genetic correlations with weights at different ages and with similar trends, increasing as age increased, in both breeds. Considering the development period analyzed, from birth to 18 months of age, the parameter maturity rate and the weights at different ages showed genetic correlations which increased until the weight at 150 and 205 days in Nelore and Chianina, respectively, and decreased from these ages on, and the genetic correlations among the parameter maturity interval and the weights at different ages were negative. They decreased until the weights at 150 and 205 days, respectively, in Nelore and Chianina, and increased from these ages on.
