The first expansion measure is to decrease the selection intensity in sires and dams: more sires and dams are selected as parents for the next generation. It facilitates the inclusion of sires and dams from the whole population and guarantees the presence of the total variation in pedigrees. A high selection intensity works in the opposite direction: it may easily lead to a limited number of selected parents not representing the total variation in pedigrees. Especially a limited number of selected sires, as is often the case in less controlled breeding programs (horses and dogs), increases the future relatedness in the population and leads to future matings between offspring of such sires resulting in inbreeding. Thus the use of more sires and dams has a favourable effect of on the average additive genetic relationship, but it should be realized that it gives less genetic improvement.
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The third expansion is to cross a limited number of selected parents with selected parents from another foreign breed. In most situations it is a handsome most convenient to buy semen from a limited number of selected sires of another the foreign breed and to inseminate a selected number of dams of your breed with this semen. The choice of the “foreign” foreign breed is crucial: when the difference in conformation and size, in adaptive traits and in breeding goal traits is large, it will take many generations to obtain acceptable offspring and it will be difficult to get support from individual breeders for crossbreeding. In a lot of species and breeds “breed purity” is a real issue to account for and the breeding standard should not be threatened.
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