A method was used to account for heterogeneous phenotypic variance for milk yield across herds and over time based on variance for each herd-year class in genetic evaluation of Minas Gerais State Holstein. Phenotypic variances increased twice as within subclass averages increased from 4,000 to 10,000 kg and also with increases in subclass size. Data were standardized to a common variance and the breeding values obtained before and after adjustment were compared. Small variations of Predicted Transmitting Abilities (PTAs) and ordering for sires were found. Rank correlations between PTAs of elite cows were small to negatives. Before adjustment for heterogeneity the elite cows originated from herds with large variability and after they were selected in all variability classes. Estimated genetic trend for milk increased by 12 kg/year after adjustment. The implementation of adjustment for heterogeneity of variance in genetic evaluation should increase the reliability of selection among top cows in the State and may increase the rate of genetic gain from female selection.
dairy cattle; genetic evaluation; heterogeneous variances; milk yield
