Institute of Agricultural and Nutritional Sciences, University of Halle, 06099 Halle, Germany.
J Dairy Sci. 2011 Aug;94(8):4140-51. doi: 10.3168/jds.2010-4101.
The objective of the present study was to conduct a stochastic simulation study on the possible benefits of an application of genomic selection in dairy cattle breeding programs according to a variety of selection schemes. In addition, the heritability of the trait in question, the accuracy of genomic breeding values, and the number of animals to be genotyped were varied. Specifically, the question of genotyping males, females, or both, was addressed. Selection schemes were compared with a young bull breeding program. The main criterion for comparison was the average of true breeding values of selected young males to be used as replacements for artificial insemination bulls. Stochastic simulations were run with 50 repetitions each to generate individuals with phenotypes, breeding values estimated by BLUP, and true breeding values. Genomic breeding values were generated from true breeding values with defined accuracy. Examined scenarios included a group of selection schemes that featured genotyping of parents of future bulls only. Such schemes can be viewed as improvements of young bull programs, and they were found to be competitive with or superior to a classical young bull program. However, a genomic breeding program usually involves at least genotyping young male candidates. A second group of selection schemes reflected this requirement. Scenarios in this group were found to be superior over the young bull program by 1.0 to 1.2 standard deviations of the average true breeding value of young male candidates. Within this group of scenarios, one scheme referred to an ideal situation under which genotypes for male calves were available without limitation. Using the average of true breeding values as the criterion for comparison, this idealistic scenario was competitive with other scenarios only if the reliability of genomic breeding values was larger than 0.50. Conventionally, not all males available will have genotypes, and the 2 most promising scenarios included a preselection step for dams of future bulls. This preselection step can be based on conventional BLUP estimated breeding values for bull dams, because differences with a scheme under which both parents and the resulting male offspring are genotyped were marginal. Genotyping of young male candidates should be the focus of activities of today's breeding organizations.
本研究旨在根据各种选择方案，对基因组选择在奶牛育种计划中的应用可能带来的益处进行随机模拟研究。此外，还对所研究性状的遗传力、基因组育种值的准确性以及需要进行基因分型的动物数量进行了研究。具体而言，还研究了对公牛、母牛或两者都进行基因分型的问题。选择方案与年轻公牛育种计划进行了比较。比较的主要标准是用于替代人工授精公牛的选定年轻公牛的平均真实育种值。通过 50 次重复进行了随机模拟，以生成具有表型、由 BLUP 估计的育种值和真实育种值的个体。基因组育种值是根据真实育种值的准确性生成的。所研究的方案包括一组仅对未来公牛的父母进行基因分型的方案。这些方案可以被视为年轻公牛计划的改进，并且被发现与经典的年轻公牛计划具有竞争力或优于其。然而，基因组育种计划通常至少需要对年轻公牛候选者进行基因分型。第二组选择方案反映了这一要求。这些方案的情景被发现比年轻公牛计划优越 1.0 到 1.2 个标准差，其平均真实育种值的年轻公牛候选者。在这组方案中，有一种方案指的是在没有限制的情况下可以获得雄性小牛基因型的理想情况。使用真实育种值的平均值作为比较的标准，只有当基因组育种值的可靠性大于 0.50 时，这种理想方案才具有竞争力。通常，并非所有可用的雄性动物都有基因型，并且最有前途的两个方案包括对未来公牛的母畜进行预筛选。此预筛选步骤可以基于常规的 BLUP 估计公牛母畜的育种值，因为与对父母和由此产生的雄性后代都进行基因分型的方案相比，差异很小。对年轻公牛候选者进行基因分型应是当今育种组织活动的重点。
