Modelling test day data from dairy cattle
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Four statistical models for genetic evaluations utilising dairy test day data are considered. These are: the fixed regression model, the random regression model, the autoregressive model and a multiple trait model. The emphasis is put on the comparison of these models in terms of their assumed covariance structure, modelling and prediction of breeding values and parameterisation. In the future one of the models should be used for a routine genetic evaluation of the Polish Black-and-White dairy cattle. Therefore, characteristics of test day data from the Polish population are given. In conclusion, it appears that thanks to its flexibility in handling heterogeneous variances during lactation, variable autocorrelation and non-uniform spacing between tests, the random regression model forms the most suitable approach.
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J. Szyda, Department of Animal Genetics, Agricultural University, Kozuchowska 7, 51-631 Wroclaw, Poland