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Abstract
The purpose of this study was to investigate the changes of predictive transmitting abilities (PTAs) and PTA trends for final score, from 1st to 2nd crop of daughters for Holstein sires. The PTAs were estimated from 2 datasets: D01 (records classified up to 2001) and D05 (records classified up to 2005). PTA change was the difference between D01 and D05 evaluations. A variety of alternative models were investigated to reduce the PTA changes and to reduce the differences between 1st and 2ndcrop trends of both PTA and MS. Allowing separate unknown parent groups for sires and dams together with additional pedigrees reduced the mean PTA change from -0.33, with single trait model, to -0.12. And, reduced the percent of sires showing drops from 74.5% to 56.4%, minimized the differences between 1st and 2nd crop trends.