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Related Experiment Videos

Method and effect of adjustment for heterogeneous variance.

G R Wiggans1, P M VanRaden

  • 1Animal Improvement Programs Laboratory, USDA, Beltsville, MD 20705-2350.

Journal of Dairy Science
|December 1, 1991
PubMed
Summary

Standardizing lactation records using heterogeneous variance adjustments improved genetic trend estimation for Holsteins, increasing milk yield predictions. This method refined breeding value accuracy by accounting for herd-specific variations.

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Area of Science:

  • Animal Science
  • Genetics
  • Dairy Cattle Evaluation

Background:

  • Lactation records exhibit significant genetic and error variance across different herds and time periods.
  • Accurate genetic evaluations require standardization to account for these heterogeneous variances.

Purpose of the Study:

  • To develop and implement a method for standardizing lactation records by adjusting for heterogeneous variances.
  • To assess the impact of this adjustment on genetic trend estimation and breeding value accuracy in Holsteins.

Main Methods:

  • Phenotypic variance was used to standardize records within herd-year-parity groups.
  • Variance estimates were regressed toward region-year-parity variance.
  • Heritability and genetic SD were adjusted based on phenotypic SD and base genetic SD.

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  • Records were weighted by heritability and herd error weights.

    • Main Results:

    • Estimated genetic trend for milk yield in Holsteins increased by approximately 5 kg/yr.
    • Predicted breeding values for older animals decreased by about 100 kg.
    • Correlations between parent and progeny information slightly increased with adjusted data.
    • Cows in high variance herds experienced the largest reductions in evaluations.

    Conclusions:

    • Adjustment for heterogeneous variance significantly impacts genetic trend estimation and breeding value accuracy.
    • The implemented method provides a more accurate basis for national dairy cattle evaluations.
    • This standardization is crucial for reliable genetic progress in dairy populations.