Accuracy of predicting genetic merit of A.I. sampled bulls for final score from pedigree information

A total of 1926 A.I. sampled Holstein bulls born from 1984 to 1988 and with first proofs from Summer 1991 to Summer 1993 were used to determine the accuracy of predicting PTAT and DTD from different sources of pedigree information obtained before the bull had daughter information. Pedigree sources used were PA, PI, PTAT_SIRE, and PTAT_DAM. Simple linear regression was used to determine which pedigree source predicted PTAT or DTD with the highest accuracy (highest R²). R² was higher for PA than had the other pedigree sources. R²s for PA to predict initial PTAT and DTD with daughter information were .59 and .18 respectively. Higher weights and R²s for PTAT than DTD resulted from the part whole relationship between PA and PTAT. Accuracy of prediction varied depending on when a bull received his first proof. R² values for PA to predict initial PTAT ranged from .35 to .69, and increased as the time of the pedigree estimate approached the date of the initial proof. R² values for PA to predict initial DTD ranged from .16 to .21 and increased as the time of the pedigree estimate approached the date of the initial proof.

The impact of the within herd variance correction which was implemented in the Summer 1993 summary was also evaluated. Correlations between PA, PI, PTAT_SIRE, and PTAT_DAM from the Winter 93 and Summer 93 evaluations were .98, .99, .99, and .96 respectively. Regression of the change in DTD estimated from previous PA minus actual DTD on PTAT_DAM S 93 - PTAT_DAM W 93 for bulls grouped by date of initial proof gave R²s from .00 to .06. It was concluded that the variance correction had little impact on the dam’s of bulls in this study.

The impact of the addition of granddaughters (son’s daughters) on the PTA of the bull dam was evaluated. The mean change in PTAT_DAM with the addition of first granddaughters was .016, indicating that the PTAT of the bull dam was slightly underestimated. R²s for the regression of the change in bull dam’s PTAT on DTD, DTD-PA, and PTAT-PA were .39, .54, and .56 respectively.

Little evidence was found to indicate a bias based on the testing population used to prove the bull. R²s for the regression of PA and PI on PTAT from the bull’s initial proof with daughter information ranged from .38 to .69, and .26 to .58 respectively. When PA and PI were used to estimate PTAT of a bull’s second proof both within and across NAAB codes, values agreed closely.