The impact of genome editing on the introduction of monogenic traits in livestock

The introduction of genome editing technologies provides new tools for the genetic improvement of animals and has the potential to become the next big game changer in animal breeding. The aim of our study was to investigate to
what extent genome editing in combination with genomic selection could accelerate the introduction of a monogenic trait as compared to a situation with genomic selection alone. A breeding population under genomic selection for
a polygenic trait was simulated. After establishing Bulmer equilibrium different selection scenarios, aiming to increase the polygenic trait and the allele frequency of the monogenic trait with or without genome editing, were compared for time to fixation of the desired allele, selection response in the polygenic trait, and level of inbreeding. In addition, the costs in terms of number of genome editing procedures were compared to the benefits of a higher cumulative proportion of the population with the desired phenotype for the monogenic trait and a lower genetic lag for the polygenic trait. Finally, the impact of efficiency of the editing procedure and survival rate of edited embryos were evaluated. Genome editing resulted in up to fourfold faster fixation of the desired allele, and the loss in long term selection response for the polygenic trait was up to threefold smaller than with genomic selection alone. In a population of 20,000 offspring per generation, the total number embryos edited to achieve fixation ranged from 22,610 with no selection to 7,080 with moderate selection and to 3,830 with high selection emphasis on the monogenic trait. With moderate selection emphasis on the monogenic trait, the total number of animals showing the undesired phenotype before fixation of the desired allele was reduced up to fourfold by adding genome editing. Genome editing had hardly any effect on inbreeding. A low editing efficiency (4%) had a major impact by increasing the number of editing procedures (+65%) and increasing the loss in selection response (+254%). Genome editing in commercial livestock breeding needs careful assessment of technical costs and benefits as well as ethical and welfare considerations.