tsehay.pdf

Summary 137
is based on equalising the genetic contribution of the founder animals to the following
generation. This could be implemented by the software package GENCONT. Under
certain constraints, the optimal number of offspring for each candidate can be
determined using this programme, to restrict the inbreeding rate and to balance the
different contribution. Generally, the restriction can be carried out on the basis of
average relationship or average inbreeding. As an alternate scenario, the restriction was
carried out through predefining the number of offspring per hen and cock, respectively.
Finally, the three scenarios were compared with the standard method of the commercial
breeding company. The result showed that high rate of genetic gain with limited
inbreeding could be achieved when using OGC. The alternate scenario resulted in
decreased breeding value for all the evaluated lines. There was no difference in genetic
response whether the maximum tolerated relationship was predefined on the basis of
average relationship or average inbreeding. Taking the overlapping generation into
account turned to have no remarkable effect.
The potential of marker assisted selection was evaluated using simulation studies. Three
types of selection strategies were compared: (1) phenotypic selection (PAS): entirely
based on phenotypic information (genotype information was not considered); (2) gene
assisted selection (GAS): selection using information on the QTL; and (3) marker
assisted selection (MAS): selection using information on markers linked to the QTL.
The comparison of PAS and GAS showed only a short-term (i.e. less than 5 generation)
advantage of GAS over PHE. GAS resulted in an increase of genetic gain by up to
20,6%. However the superiority of GAS declined in the long-term (i.e. greater than 5
generation). The genetic gain achieved with MAS and PAS was identical.
The effect of number of alleles per marker and length of chromosome segment was also
evaluated. Simulations were carried out for three types of selection strategies (PAS,
MAS and GAS) during 10 generations. At first, the number of alleles per marker was
increased from 2 to 10. However, extra genetic gain couldn’t be achieved when
increasing the number of marker alleles. Increasing the length of the chromosome
segment didn’t have any effect on genetic gain either. This suggests that the information
content of each marker genotype is more important than the number of alleles per
marker and length of chromosome segment, respectively.