Breeding strategy in small and closed livestock populations

This paper reviews the main characteristics of small and/or closed livestock populations. Although the emphasis during the realization of the genetic improvement in animal breeding is put on commercial breeding programmes, autochthonous breeds, races, strains, even herds of domestic animas, at the same time represent a potentially important segment for achieving the maintenance of the overall livestock production. These programmes are particularly important for the improvement of populations of animal genetic resources, as well as for the improvement of production in rural marginal areas. One of the main parameters for determining the size, and also the potential danger of a population is a so called effective size of the population (Ne). This parameter is determined according to the available number of male and female head of breeding stock in the population or in the herd and it varies under the influence of the sexes, changes in the size of the families, changes in the size of the population during time, as well as overlapping of the generations. Apart from the improvement of the economically important traits, the breeding programmes in small populations first of all must provide the increase of the effective size of the population aiming to limit or decrease the inbreeding, as well as the decrease of the variance in the size of the family. This is mainly achieved with so called "circular breeding plans" the sires being replaced by sons in the reproduction, and dams by daughters. The shortage of the generation interval by the change of the presence of some age categories i.e. larger number of young animals and animals that are at the peak of production comparing to a small number of older animals, can additionally influence on the genetic improvement of the traits.