In spite of being controversial and raising ethical concerns, the application of gene editing is more likely to be accepted when it contributes to improving animal welfare. One of the animal welfare and ethical issues in chicken breeding is chick culling, the killing of the male layer chicks after hatching due to the poor fattening performance. Although establishing dual-purpose chicken lines could solve this problem, unfavorable genetic correlations between egg and meat production traits hindered their competitiveness. Although it is also controversial in ethical terms, gene editing may accelerate genetic progress in dual-purpose chicken and alleviate the ethical concerns from chick culling. The simulation compared the utility improvement in dual-purpose use under two breeding schemes: one consisting in the improvement of the laying hens, and the second in the improvement of a synthetic line obtained from a layer broiler cross. In each breeding scheme, the breeding programs were simulated with and without gene editing. Polygenic breeding values and 500 simulated quantitative trait loci (QTL) with different levels of pleiotropy caused negative correlations between egg production, meat production, and overall health. The results of the simulation demonstrated that genetic gain could be accelerated by at most 81% for several generations if gene editing was used. The actual increase in genetic gain depended on the number of single nucleotide polymorphisms (SNPs) being edited per animal. The rate of genetic improvement became equal in scenarios with and without gene editing after 20 generations. This is because the remaining segregating QTL had small effects and their edition would have negative overall health effects from potential off-target edits. Although gene editing can improve genetic gain in quantitative traits, it can only be recommended as long as QTL with reasonable effect sizes are segregating and detectable. This simulation demonstrates the potential of gene editing to accelerate the simultaneous improvement of negatively correlated traits. When the risk of negative consequences from gene editing persists, the number of SNPs to be edited should be chosen carefully to obtain the optimal genetic gain.

中文翻译：

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模拟实施基因编辑的两用鸡育种计划


尽管存在争议并引发伦理问题，但当基因编辑有助于改善动物福利时，它的应用更有可能被接受。鸡饲养中的动物福利和伦理问题之一是雏鸡扑杀，即由于育肥性能差而在孵化后杀死雄性蛋鸡。尽管建立双用途鸡系可以解决这个问题，但产蛋性状和产肉性状之间不利的遗传相关性阻碍了它们的竞争力。尽管在伦理方面也存在争议，但基因编辑可能会加速两用鸡的遗传进展，并减轻雏鸡扑杀带来的伦理问题。该模拟比较了两种育种方案下双重用途的效用改进：一种是蛋鸡的改良，另一种是对从蛋鸡杂交获得的合成品系的改良。在每个育种方案中，都模拟了有或没有基因编辑的育种程序。多基因育种值和 500 个具有不同多效性水平的模拟数量性状基因座 (QTL) 导致产蛋量、产肉量和整体健康之间呈负相关。模拟结果表明，如果使用基因编辑，几代人的遗传增益最多可加速 81%。遗传增益的实际增加取决于每只动物编辑的单核苷酸多态性 (SNP) 的数量。 20代后，有和没有基因编辑的情况下，遗传改良率变得相等。这是因为剩余的分离 QTL 影响较小，并且它们的版本会对潜在的脱靶编辑产生负面的整体健康影响。 尽管基因编辑可以提高数量性状的遗传增益，但只有在具有合理效应大小的 QTL 被分离和可检测的情况下才可以推荐。该模拟证明了基因编辑加速负相关性状同时改善的潜力。当基因编辑带来负面后果的风险持续存在时，应谨慎选择要编辑的 SNP 数量，以获得最佳遗传增益。