Verena Gonzalez Lopez, 2011 - Institut für Tierzucht und Tierhaltung ...

Discussion
In the last 15 years, selection schemes in Piétrain herdbook population in SH are
characterized by the widespread use of genetically superior proven boars. Especially
the boar to sow selection path is dominated by only a few boars (Gonzalez Lopez et
al., 2011). Furthermore, BLUP based selection, which has been applied since 1990
in the local population, has led to an increased probability of coselecting related
animals. Both circumstances increased the inbreeding level in the population in past
decades and resulted in an effective population size of around 100 animals
(Gonzalez Lopez et al., 2011). Such developments are typical in systematically bred
livestock populations and were also extensively investigated in cattle populations. For
example Sorenson et al. (2004) identified eight ancestors that together accounted for
about 50% of the genes of reference population and estimated an effective
population size of 70 animals in Danish Holsteins.
Increased rates of inbreeding might result in detrimental effect in the long term
through a reduction in genetic variability, higher chance of appearance of undesired
recessive disorders and increased inbreeding depression (Falconer and Mackay,
1996). Therefore, breeding organizations focus much more on joint control of genetic
progress and inbreeding in recent years.
Several selection methods have been described to maximize genetic progress while
constraining inbreeding (Woolliams and Meuwissen, 1993; Wray and Goddard, 1994;
Brisbane and Gibson, 1995; Meuwissen and Goddard, 1997; Meuwissen, 1997). The
optimum contribution method (Meuwissen 1997), implemented in the program
GENCONT, has been analyzed in detail using both simulation studies (Sonesson
und Meuwissen, 2002) and data from practical breeding programs, for example in
five US dairy breeds (Weigel and Lin, 2002), in beef cattle and a sheep population
(Avendaño et al., 2003) as well as in the UK Holstein population (Kearney et al.,
2004). So far, however, only a limited number of optimum contribution selection
applications in pig breeding programs were published. One example is the study of
Hanenberg and Merks (2001), in which results from optimum contribution selection
application with an equal contribution approach in a closed pig breeding program
were compared. They found that the use of optimum contribution selection can
improve genetic gain up to 22% at the same rate of inbreeding. Similar results were
reported by Meuwissen (1997) and Grundy et al. (1998) who used simulation studies
to evaluate optimum contribution theory compared with BLUP truncation selection.
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