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From the previous it has become clear that decrease in selected proportion, so an An increase in selection intensity, results in an increase in genetic gain. Fast genetic gain can thus be achieved by selecting only the very few very best animals for breeding. That is simple, why not do that? Apart from the fact that the reproductive capacity will determine the minimum number of animals that need to be selected in order to maintain population size, there is another important issue: inbreeding. Remember from the chapter about genetic relationship and inbreeding that the The rate of inbreeding in a population can be predicted by 1/8N_m + 1/8N_f and that a smaller number of parents thus results in a higher rate of inbreeding. Especially in case of This is especially the case with unbalanced numbers of males and females. If we use the recommendation of the FAO not exceed the rate of inbreeding of 0.5 to 1% for the population to remain viable, this may have consequences for the selection strategy.

In large populations, for the same rate of inbreeding, larger selection intensities can be applied than in small populations. For example, in a a large population of 20,000 animals (half male, half female) a selected proportion of 1% would result in 100 selected animals. Equal selected proportions in males and females would result in a rate of inbreeding of 0.25%. If, however, this population was not 20,000 but only 2000 animals large, then In a small population of 2000 animals a selected proportion of 1% in males and females would result in a rate of inbreeding of 2.5%, which is too large. Often the selected proportion in of males is ( much ) smaller than in females. If we take the population of 20,000 animals again, a selected proportion of 0.1% in males (select the best 10 males) and use all 10,000 females for breeding, results in a rate of inbreeding of 1.25% (1.25125 to be precise). Despite the fact that 10,010 animals are used for breeding, the rate of inbreeding is still too high for the population to remain viable. And with AI 1000 offspring per sire in most species is not a problem, provided sufficient number of females are available.Breeding companies earn their income from selling genetic material (usually sperm). So it is in their interest to keep their breeding stock viable. However, there are competing breeding , which is too high.

Breeding companies are competing companies who want to provide the same market of genetic material. Breeding companies solve this conflict by trying Therefore, they try to make as much genetic progress as possible to keep (or increase) market share, but restrict the rate of inbreeding to 1%.

Thus:

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