The effect of milk sampling procedures on the robustness of genetic evaluation in dairy cattle
Abstract
English: The study was divided into three separate sections. Firstly the influence of
selection is investigated by means of simulating a population including selection in
the model and then simulating data with out selection. In the second section the
simulation process was validated by determining how well the breeding values and
the resulting variance components were predicted under DFREML procedures.
This was done by the calculation of the fixed effect, variance components and
product moment correlation between the estimated breeding values and the
simulated breeding values. In the third section a multiple trait analysis was done in
order to determine the relationship between the single and composite sample.
The effect of selection showed a substantial overestimation of the fixed effect and
the resulting variance component estimates. Various authors (Hagger, 1991;
Tuchsceherer & Herrendërfer, 1998, van der Werf, 1990) supported these results
and this effect can be attributed to fact that all information on all animals in the
analysis should be available to compensate for selection.
The product moment correlation between the true genetic component and the
breeding values determined by DFREML as well as the estimated variance
components confirmed that the simulation process and the model used to simulate
data can be applied to simulate data. These results were used in a multiple trait
analysis to evaluate the difference between a single and composite sample
analysis. Results from multiple trait analysis showed a high genetic correlation
between the breeding values of the composite and single sample. This indicates
that the same genes are responsible for both traits and that it is indeed possible to
make use of a single sample instead of a composite sample. Afrikaans: Die studie was in drie afsonderlike seksies opgedeel. In die eerste afdeling is die
effek van seleksie ondersoek deur middel van die simulasie van data met en sonder
seleksie. In die tweede afdeling word die simulasie proses ondersoek deur gebruik
te maak van die teelwaardes en die variansie komponente soos bepaal deur
DFREML. Dit is gedoen om die simulasie te verifiseer. Tydens die derde en finale
afdeling word 'n veelvoudige eienskap analise gedoen om die verwantskap tussen
die enkel en saamgestelde monster te bepaal.
Die effek van seleksie op 'n ontleding vir die bepaling van teelwaardes word
duidellik aangetoon in die eerste afdeling. 'n Aansienlike oorberaming van die
vaste effek word verkry en word toegeskryf aan die feit dat alle inligting
aangaande elke dier wat in die analise gebruik word, beskikbaar moet wees vir
ontleding. Hierdie bevinding word deur verskeie outeurs in die literatuur
ondersteun (Hagger, 1991; Tuchsceherer & Herrendorfer, 1998, van der Werf,
1990).
Die korrelasie tussen die teeltwaardes van die gesimuleerde data en die
teeltwaardes soos beplaal deur DFREML (Meyer, 1995) asook die beraamde
variansie komponente het getoon dat die simulasie proses en die model wat
gebruik is korrek is en nou gebruik kon word vir die vergelyking tussen 'n enkel en
dubbel monster. 'n Veelvoudige eienskap analise tussen die enkel en dubbel
monster het 'n hoe genetiese korrelsie tussen die twee eienskappe getoon. Dit
impliseer dat dieselfe gene verantwoordelik is vir die bepaling van beide
eienskappe en dat dit wel moontlik is om die dubbel monster met die enkel
monster te vervang.