The effect of milk sampling procedures on the robustness of genetic evaluation in dairy cattle

[摘要] English: The study was divided into three separate sections. Firstly the influence ofselection is investigated by means of simulating a population including selection inthe model and then simulating data with out selection. In the second section thesimulation process was validated by determining how well the breeding values andthe resulting variance components were predicted under DFREML procedures.This was done by the calculation of the fixed effect, variance components andproduct moment correlation between the estimated breeding values and thesimulated breeding values. In the third section a multiple trait analysis was done inorder to determine the relationship between the single and composite sample.The effect of selection showed a substantial overestimation of the fixed effect andthe resulting variance component estimates. Various authors (Hagger, 1991;Tuchsceherer & Herrendërfer, 1998, van der Werf, 1990) supported these resultsand this effect can be attributed to fact that all information on all animals in theanalysis should be available to compensate for selection.The product moment correlation between the true genetic component and thebreeding values determined by DFREML as well as the estimated variancecomponents confirmed that the simulation process and the model used to simulatedata can be applied to simulate data. These results were used in a multiple traitanalysis to evaluate the difference between a single and composite sampleanalysis. Results from multiple trait analysis showed a high genetic correlationbetween the breeding values of the composite and single sample. This indicatesthat the same genes are responsible for both traits and that it is indeed possible tomake use of a single sample instead of a composite sample.

[发布机构] University of the Free State