Estimates of genetic parameters and an evaluation of genotype x environment interaction for weaning weight in Nellore cattle.

Records of 105,645 Nellore calves born from 1977 to 1994 in eight different regions of Brazil were used to estimate genetic and environmental parameters and evaluate genotype x environmental interaction for weaning weight (kg). Estimates were obtained using MTDFREML with a sire model. Mathematical model included random effects of sire and dam, and fixed effects of sex, month and year of birth, herd, and age of dam at calving. Estimates of phenotypic variances were 375, 431, 431, 407, 409, 400, 413, and 336 for the eight different regions and 420 over all regions. Estimates of heritability were, respectively, 0.22, 0.26, 0.16, 0.29, 0.34, 0.38, 0.37, 0.26, and 0.26. Heritability estimates for weaning weights from two trait analyses with measurements in different regions considered as different traits varied from 0.17 to 0.38 and estimated genetic correlations among weaning weights in different regions varied from - 0.03 to 1.00. Spearman rank correlations between EPDs for weaning weight from different regions were calculated to verify whether sires ranked differently in different regions. The correlations ranged from - 0.25 to 1.00 between pairs of regions. Estimates of heritability suggest that mass selection could result in genetic gain under a breeding program that utilizes weaning weight as a selection criterion. The apparent importance of genotype x environment interaction detected by this study suggests a need to choose sires appropriate for the region where they will be used, since relative performance of progeny of a sire appears to change from one region to another