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Genetic relationship of milk yield for different parities between bulls and their sons

Genetic relationship of milk yield for different parities between bulls and their sons. Objectives. Determine whether bulls differ in maturity rate of their daughters Confirm that those differences are transmitted across generations. Data.

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Genetic relationship of milk yield for different parities between bulls and their sons

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  1. Genetic relationship of milk yield for different parities between bulls and their sons

  2. Objectives • Determine whether bulls differ in maturity rate of their daughters • Confirm that those differences are transmitted across generations

  3. Data • Standardized lactation milk records for Holstein parities 1 through 3 • Cows first calving between 1960 and 1998 • No missed parities before cow exited herd • Only records from first herd included

  4. Methods Three PTA calculated for each bull using current USDA-DHIA animal model PTA1 based on records from parity 1 of daughters and their contemporaries PTA1,2 based on records from parities 1 and 2 of daughters and their contemporaries PTA1,2,3 based on records from parities 1, 2, and 3 of daughters and their contemporaries

  5. Methods (cont.) Number of records n1 = number of bull’s daughters with first parity records n2 = number of bull’s daughters with second parity records n3 = number of bull’s daughters with third parity records

  6. Methods (cont.) Solutions for biological contributions of parities 2 (PTA2) and 3 (PTA3) derived from

  7. Results • 2864 bulls with genetic evaluations based on 500 daughters • Difference between PTA1 and PTA1,2,3 ranged from 290 to 295 kg of milk; SD of 85 kg • Difference between PTA1 and PTA3 ranged from 610 to 555 kg of milk; SD of 179 kg

  8. Results (cont.) • PTA1,2 intermediate to PTA1 and PTA1,2,3 • (PTA1,2 PTA1) regressed on (PTA1,2,3 PTA1) b = 0.725, R = 0.971 • (PTA2 PTA1) regressed on (PTA3 PTA1) b = 0.725, R = 0.852 • Primarily same genetic control for parities 2 and 3

  9. Impact of daughter maturity rate

  10. Correlation between parity PTA for milk (1996 vs 1999)

  11. Results (cont.) • 16,643 sons with genetic evaluations based on 40 daughters • Expected regressions of son PTA on sire PTA (calculated within sire and son birth year) between 0.44 and 0.50 • Actual regressions near expectations

  12. Regression of son PTA on sire PTA for milk yield

  13. Regression of son PTA on sire PTA for milk yield (cont.)

  14. Conclusions • Differences in daughter maturity rate are large enough to impact evaluation accuracy, if genetic. • Differences are transmitted from sires to sons (genetic confirmation).

  15. Conclusions • Modeling separate PTA for each parity should: • Increase accuracy of genetic evaluations • Reduce oscillation in bull evaluations when records per daughter change considerably • Most noticeable in high reliability bulls

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