Wang Yu, Bennewitz Jörn, Wellmann Robin
Institute of Animal Science, University of Hohenheim, 70593, Stuttgart, Germany.
Genet Sel Evol. 2017 May 12;49(1):45. doi: 10.1186/s12711-017-0320-7.
Optimum contribution selection (OCS) is effective for increasing genetic gain, controlling the rate of inbreeding and enables maintenance of genetic diversity. However, this diversity may be caused by high migrant contributions (MC) in the population due to introgression of genetic material from other breeds, which can threaten the conservation of small local populations. Therefore, breeding objectives should not only focus on increasing genetic gains but also on maintaining genetic originality and diversity of native alleles. This study aimed at investigating whether OCS was improved by including MC and modified kinships that account for breed origin of alleles. Three objective functions were considered for minimizing kinship, minimizing MC and maximizing genetic gain in the offspring generation, and we investigated their effects on German Angler and Vorderwald cattle.
In most scenarios, the results were similar for Angler and Vorderwald cattle. A significant positive correlation between MC and estimated breeding values of the selection candidates was observed for both breeds, thus traditional OCS would increase MC. Optimization was performed under the condition that the rate of inbreeding did not exceed 1% and at least 30% of the maximum progress was achieved for all other criteria. Although traditional OCS provided the highest breeding values under restriction of classical kinship, the magnitude of MC in the progeny generation was not controlled. When MC were constrained or minimized, the kinship at native alleles increased compared to the reference scenario. Thus, in addition to constraining MC, constraining kinship at native alleles is required to ensure that native genetic diversity is maintained. When kinship at native alleles was constrained, the classical kinship was automatically lowered in most cases and more sires were selected. However, the average breeding value in the next generation was also lower than that obtained with traditional OCS.
For local breeds with historical introgressions, current breeding programs should focus on increasing genetic gain and controlling inbreeding, as well as maintaining the genetic originality of the breeds and the diversity of native alleles via the inclusion of MC and kinship at native alleles in the OCS process.
最优贡献选择（OCS）对于提高遗传增益、控制近亲繁殖率以及维持遗传多样性是有效的。然而，由于其他品种遗传物质的渗入，种群中较高的迁移贡献（MC）可能导致这种多样性，这可能会威胁到当地小种群的保护。因此，育种目标不仅应侧重于提高遗传增益，还应注重保持本地等位基因的遗传原真性和多样性。本研究旨在调查通过纳入MC和考虑等位基因品种来源的修正亲缘关系是否能改进OCS。考虑了三个目标函数，分别是使亲缘关系最小化、使MC最小化以及使后代世代的遗传增益最大化，并且我们研究了它们对德国安格勒牛和前瓦尔代尔牛的影响。
在大多数情况下，安格勒牛和前瓦尔代尔牛的结果相似。两个品种的选择候选个体的MC与估计育种值之间均观察到显著的正相关，因此传统的OCS会增加MC。在近亲繁殖率不超过1%且所有其他标准至少达到最大进展的30%的条件下进行优化。尽管传统的OCS在经典亲缘关系限制下提供了最高的育种值，但后代世代中MC的大小未得到控制。当MC受到限制或最小化时，与参考方案相比，本地等位基因的亲缘关系增加。因此，除了限制MC外，还需要限制本地等位基因的亲缘关系以确保维持本地遗传多样性。当本地等位基因的亲缘关系受到限制时，在大多数情况下经典亲缘关系会自动降低，并且会选择更多的公牛。然而，下一代的平均育种值也低于传统OCS获得的值。
对于有历史基因渗入的地方品种，当前的育种计划应侧重于提高遗传增益和控制近亲繁殖，以及通过在OCS过程中纳入MC和本地等位基因的亲缘关系来维持品种的遗传原真性和本地等位基因的多样性。
