The objective of this study was to estimate (co)variance components and genetic parameters, such as heritabilities and correlations, and genetic and phenotypic trends for birth weight (PN), weaning weight (PD) and 205 day adjusted weight gain (GNDA). A total of 23,369 records on animals, born from 1980 through 2000, collected by PROMEBO - beef cattle improvement program of Associação Nacional de Criadores Herd Book Collares, were used. Of these animals, 16,593 had record of PN, 22,530 had of PD and 22,259 of GNDA. Analyses were performed by the restricted maximum likelihood method using the MTDFREML program. Initially, a univariate analysis was used for each trait and, afterwards, bivariate models were used in analyses relating weights at birth and weaning with pre-weaning gain. Heritabilities and standard errors obtained from univariate analyses were of 0.32 ± 0.03 for PN, 0.17 ± 0.01 for GNDA and of 0,12 ± 0,01 for PD. From bivariate analyses of PN with GNDA and of PD with GNDA, heritability estimates were of 0.35 and 0.17 and of 0,32 and 0.42, respectively. Medium heritabilities for weights and weight gains indicate that these traits efficiently respond to selection. Genetic correlation estimates was high (0.95) between PD and GNDA and low (0.15) between PN and GNDA indicating that selection for weight gain make it possible to obtain a correlated response on weaning weight, without increasing birth weight. Estimated genetic and phenotypic trends demonstrated genetic progress for GNDA and PD, while PN is on plateau, thereby, indicating favorable change in pre-weaning performance, without increasing risk of calving difficulty.
correlations; heritability; maternal effect; pre-weaning
