In this case, genetic introgression with other breeds may be not avoidable but should be restricted. For these breeds, the main objective of the breeding program is to maintain or to increase genetic diversity by minimizing the mean kinship in the population. dog breeds), accurate breeding values for total merit are not available and historical genetic bottlenecks have depleted their gene pool. In contrast, for many companion breeds (e.g. This means to reduce their genetic contribution from non-endangered breeds, to conserve the genetic diversity at native haplotype segments, and to maintain a sufficient genetic distance to non-endangered breeds. Hence, breeding programs for local breeds with historic introgression have the additional objective to recover the original genetic background of the breed. This displacement crossing has often progressed to the point where the original genetic background of the local breed must be considered endangered.
High performance livestock breeds, however, have often been used for upgrading local breeds. This approach is the classical optimum contribution selection (OCS) proposed by. Thus, the optimum contributions of the selection candidates are the solution of an optimization problem where the objective is to maximize the mean breeding value in the offspring while the increase in mean kinship in the population is constrained.
Maintenance of a sufficient effective size is achieved by restricting the rate of increase in mean kinship. In any case, however, selecting animals for breeding in the optimum way requires to compute the genetic contribution each selection candidate should have to the next generation.įor high-performance livestock breeds, the objective of a breeding program is to maximize genetic gain while at the same time a sufficient effective size of the breed should be maintained to avoid inbreeding depression or a depletion of the additive genetic variance. The objectives of breeding programs for livestock breeds, companion animals, and zoo populations of endangered species may be quite different.
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