Simulation of introgression of the polled allele into the Jersey breed via conventional breeding versus gene editing

Authors: MUELLER, MACI - University Of California, Davis; Cole, John; SONSTEGARD, TAD - Recombinetics, Inc; VAN EENENNAAM, ALISON - University Of California, Davis

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/14/2018
Publication Date: 9/1/2018
Citation: Mueller, M.L., Cole, J.B., Sonstegard, T.S., Van Eenennaam, A.L. 2018. Simulation of introgression of the polled allele into the Jersey breed via conventional breeding versus gene editing. Translational Animal Science. 2(Suppl. 1):S57–S60. 10.1093/tas/txy054.
DOI: https://doi.org/10.1093/tas/txy054

Interpretive Summary:

Technical Abstract: Dehorning is a standard cattle management practice to protect animals and humans from injury. It is an unpleasant, costly process subject to increased public scrutiny as an animal welfare issue. Horns are a recessively inherited trait, so an alternative is to breed for polled (hornless). However, this approach has not been widely adopted due to the limited number of high genetic merit polled sires available. Recently, gene editing for polled has been proposed as solution. Our hypothesis was that gene editing is a more efficient method than conventional breeding for decreasing the horned allele frequency in Jersey cattle, while keeping inbreeding at acceptable levels and maintaining genetic progress. To test this hypothesis, computer simulation was used to model introgression of the polled allele into the U.S. Jersey cattle population via conventional breeding or gene editing for three different polled mating schemes, for a total of six polled scenarios. Each scenario’s results were averaged over ten replicates and changes in horned allele frequency, levels of inbreeding and genetic gain were determined. The use of gene editing decreased the horned allele frequency to < 60% within five years, which was more efficient than conventional breeding. When herds were forced to use only homozygous polled (PP) sires, inbreeding reached 14%. However, the use of gene editing in the same mating scheme decreased inbreeding to 8%. Gene editing resulted in greater genetic gain on average ($15 - $29 per year) compared to conventional breeding. The optimal polled mating scenario used both PP and horned (pp) sires in combination with gene editing. These results confirm our hypothesis that gene editing of the polled locus could be used to effectively address dairy producers’ economic concerns, while also alleviating consumers’ animal welfare concerns.