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The number sires and dams and the variation in the number of their offspring determine the genetic composition of the next generation of their offspring. The variation in the number of their offspring is of great importance. In well controlled breeding programs it is tried to keep this variance as small as possible: it is tried to get an equal number of progeny selected individual. But in a lot of species dams give birth to multiple offspring and then variation in litter size is always present. In less controlled breeding programs a lot of variation is often found in the number of offspring per sire. Popularity of sires is responsible for that: show champions are widely and often unlimitedly used as sires. The number of animals that contribute in different extend to the next generation is crucial in the management of a population when you aim at reducing the rate of inbreeding.