tsehay.pdf

Summary 136
8 Summary
Studies on the design of breeding programs in the breeding of laying hens.
The primary objective of the present study was to analyse the conventional layer
breeding. Among others, inbreeding, selection response, different selection and mating
strategies were evaluated for this purpose. Finally, modern methods and optimization
concepts were designed to improve the layer breeding programs based on the research
results of conventional layer breeding schemes. Three lines of commercial Lohmann
LSL layers were used for the evaluation. For these lines, different scenarios were
simulated, including the mating system, the number of selected hens and cocks as well
as homozygosity. Selected number of hens and cocks was modified to test the effect on
selection response.
Three groups of 500, 1500 and 4,000 animals in single cage housing systems were used
for the simulation study. The study showed that in a large flock of 4000 single cages,
highest selection response was achieved by selecting 500 hens and 50 cocks. In a
medium flock of 1500 single cages, the selection of 200 hens and 50 cocks were
optimal. In a small (reserve) flock of 500 single cages, high selection response could be
achieved by selecting 120 hens and 30 cocks.
The comparison of different mating systems showed that the average inbreeding
coefficient when using assortative mating was 91% higher compared to that of random
mating. However, assortative mating resulted in an increase in genetic response of only
5% compared with random mating. The genetic response and inbreeding with minimum
coancestry mating and disassortative mating were below random mating. Therefore,
regarding selection response and inbreeding, the choice of the appropriate mating
system is of great importance.
The simulation showed, based on the population under study, the loss of alleles within
10 generations. After 10 generations of selection, from originally 100 alleles of 50
founder sires and 1000 alleles of 500 founder dams, respectively, remained less than
only18 different alleles in the large flock.
In this study, the optimum genetic contribution (OGC) theory (Meuwissen, 1997) was
applied to maximize the genetic response at a predefined rate of inbreeding. The theory