PDF(Pubmed)
Abstract：
Initial findings on genomic selection (GS) indicated substantial improvement for major traits, such as performance, and even successful selection for antagonistic traits. However, recent unofficial reports indicate an increased frequency of deterioration of secondary traits. This phenomenon may arise due to the mismatch between the accelerated selection process and resource allocation. Traits explicitly or implicitly accounted for by a selection index move toward the desired direction, whereas neglected traits change according to the genetic correlations with selected traits. Historically, the first stage of commercial genetic selection focused on production traits. After long-term selection, production traits improved, whereas fitness traits deteriorated, although this deterioration was partially compensated for by constantly improving management. Adding these fitness traits to the breeding objective and the used selection index also helped offset their decline while promoting long-term gains. Subsequently, the trend in observed fitness traits was a combination of a negative response due to genetic antagonism, positive response from inclusion in the selection index, and a positive effect of improving management. Under GS, the genetic trends accelerate, especially for well-recorded higher heritability traits, magnifying the negatively correlated responses for fitness traits. Then, the observed trend for fitness traits can become negative, especially because management modifications do not accelerate under GS. Additional deterioration can occur due to the rapid turnover of GS, as heritabilities for production traits can decline and the genetic antagonism between production and fitness traits can intensify. If the genetic parameters are not updated, the selection index will be inaccurate, and the intended gains will not occur. While the deterioration can accelerate for unrecorded or sparsely recorded fitness traits, GS can lead to an improvement for widely recorded fitness traits. In the context of GS, it is crucial to look for unexpected changes in relevant traits and take rapid steps to prevent further declines, especially in secondary traits. Changes can be anticipated by investigating the temporal dynamics of genetic parameters, especially genetic correlations. However, new methods are needed to estimate genetic parameters for the last generation with large amounts of genomic data.
Initial findings on genomic selection indicated substantial improvement for major traits such as growth or milk yield and even successful selection for secondary traits such as fertility or survival. However, recent unofficial reports indicate an increased frequency of problems in several secondary traits. This study looks at potential sources of those problems and mitigation strategies. Under selection initially carried out for production traits, production improved, but fertility (i.e., a secondary trait) declined, with the decline partially compensated for by improving management. Later, also because the observed deteriorations were becoming too strong, these traits became part of the breeding objectives, and used selection indexes were modified to include secondary traits, halting the deterioration. Under genomic selection, genetic gains accelerate, especially for higher heritability production traits, potentially magnifying the negative responses for secondary traits, and management modifications may not be fast enough to alleviate the decline. The responses can especially decline for unrecorded or sparsely recorded fitness traits. While the decline may be slow and hard to see, it may be serious in the long term and hard to reverse. Changes under genomic selection may be monitored by recalculating genetic parameters every generation. Secondary traits that become more antagonistic with production traits will likely deteriorate more and will need special attention.
Initial findings on genomic selection indicated substantial improvement for major traits such as growth or milk yield and even successful selection for secondary traits such as fertility or survival. However, recent unofficial reports indicate an increased frequency of problems in several secondary traits. This study looks at potential sources of those problems and mitigation strategies. Under selection initially carried out for production traits, production improved, but fertility (i.e., a secondary trait) declined, with the decline partially compensated for by improving management. Later, also because the observed deteriorations were becoming too strong, these traits became part of the breeding objectives, and used selection indexes were modified to include secondary traits, halting the deterioration. Under genomic selection, genetic gains accelerate, especially for higher heritability production traits, potentially magnifying the negative responses for secondary traits, and management modifications may not be fast enough to alleviate the decline. The responses can especially decline for unrecorded or sparsely recorded fitness traits. While the decline may be slow and hard to see, it may be serious in the long term and hard to reverse. Changes under genomic selection may be monitored by recalculating genetic parameters every generation. Secondary traits that become more antagonistic with production traits will likely deteriorate more and will need special attention.
摘要：
基因组选择的初步发现表明主要性状有了实质性改善，比如性能，甚至成功选择拮抗性状。然而,最近的非官方报告表明，次生性状恶化的频率增加。这种现象可能由于加速的选择过程和资源分配之间的不匹配而出现。由选择索引明确或隐含地说明的特征朝着期望的方向移动，而忽略的性状根据与所选性状的遗传相关性而变化。历史上,商业遗传选择的第一阶段集中在生产性状上。经过长期挑选,生产性状得到改善，而健康特征恶化，尽管这种恶化通过不断改进管理得到了部分补偿。将这些适应度性状添加到育种目标和使用的选择指数中也有助于抵消其下降，同时促进长期收益。随后，观察到的适应度特征的趋势是由于遗传拮抗作用引起的负面反应的组合，纳入选择指数的积极响应，和改善管理的积极作用。在基因组选择下，基因趋势加速，特别是对于记录良好的高遗传力性状，放大适应度性状的负相关反应。然后，观察到的健康特征趋势可能会变得消极，特别是因为在基因组选择下，管理修改不会加速。由于基因组选择的快速周转，可能会发生额外的恶化，由于生产性状的遗传力会下降，生产性状和适应性性状之间的遗传拮抗作用会加剧。如果遗传参数没有更新，选择指数将不准确，而预期的收益就不会发生。虽然对于未记录或稀疏记录的健身特征，恶化会加速，基因组选择可以改善广泛记录的适应度特征。在基因组选择的背景下，寻找相关特征的意外变化并迅速采取措施防止进一步下降是至关重要的，尤其是在次要性状上。可以通过调查遗传参数的时间动态来预测变化，尤其是遗传相关性。然而,需要新的方法来估计最后一代的遗传参数与大量的基因组数据。
