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Adjustments for heterogeneous herd-year variances in a random regression model for genetic evaluations of Polish Black-and-White cattle

100%

Strabel T., Jankowski T., Jamrozik J.

Journal of Applied Genetics

2006

vol. 47

issue 2

125-130

The study investigated the existence of heterogeneous variance in first-lactation daily milk yield of Polish Black-and-White cows across herds in different years. Bayesian Information Criterion was used to show that the model with unequal residual variances for different herd-years was more plausible than the model assuming equal variances. A method of adjusting phenotypic records was developed to account for unequal variability in herd-years. Factors used for the data adjustment considered variation of general residuals and residuals for specific herd-years. The size of herd-year was also taken into account. Varied power of corrections was used to analyze the effect of adjustment on estimated breeding values. The method was applied to daily milk records of 817 165 primiparous cows. The effectiveness of the data adjustment was evaluated by the analysis of differences between each bull's breeding value and its parental index. Data correction reduced the average difference and variance of differences between breeding values and parental indices. Accounting for the size of herd-year classes in correction factors improved the efficiency of heterogeneous variance adjustment.

The selection index and single- and multi-trait animal model evaluation of Polish Black-and-White cows

80%

Jagusiak W., Zarnecki A.

Journal of Applied Genetics

2000

vol. 41

issue 3

171-179

The selection index and single- and multi-trait animal models were used for genetic evaluation of 100,983 cows. Genetic and environmenta? al (co)variances of five milk production traits were estimated using MTDFREML. The highest heritabilities were found for fat and protein contents in all three lactations (0.29-0.33), and the lowest for protein yield in the third lactation (0.08). Phenotypic and genetic correlations between yield traits in adjacent lactations were higher than between the first and third lactations. Correlations between breeding values for fat content were higher than for yield traits. The magnitude of correlations between the index and animal model evaluations depended on the number of lactation records included in both procedures. Usually the relationships between breeding values based on the same lactations were close to unity. The correlations between single-trait and multi-trait evaluations decreased with increasing numbers of lactations in the model. This was the result of using variances and covariances of later lactations in the multi-trait model.

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2 Journal of Applied Genetics

1 2006

1 2000

1 Jagusiak W.

1 Jamrozik J.

1 Jankowski T.

1 Strabel T.

1 Zarnecki A.

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Adjustments for heterogeneous herd-year variances in a random regression model for genetic evaluations of Polish Black-and-White cattle

The selection index and single- and multi-trait animal model evaluation of Polish Black-and-White cows