Comparison of gene editing versus conventional breeding to introgress the POLLED allele into the US dairy cattle population

• Published in: Journal of dairy science 2019-05, Vol.102 (5), p.4215-4226
• Main Authors: Mueller, M.L., Cole, J.B., Sonstegard, T.S., Van Eenennaam, A.L.
• Format: Article
• Language: English
• Subjects: gene editing; Holstein; Jersey; polled; simulation
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2018-15892

Disbudding and dehorning are commonly used cattle management practices to protect animals and humans from injury. They are unpleasant, costly processes subject to increased public scrutiny as an animal welfare issue. Horns are a recessively inherited trait, so one option to eliminate dehorning is to breed for polled (hornlessness). However, due to the low genetic merit and scarcity of polled dairy sires, this approach has not been widely adopted. In March 2018, only 3 Holstein and 0 Jersey active homozygous polled sires were registered with the National Association of Animal Breeders. Alternatively, gene editing to produce high-genetic-merit polled sires has been proposed. To further explore this concept, introgression of the POLLED allele into both the US Holstein and Jersey cattle populations via conventional breeding or gene editing (top 1% of bulls/year) was simulated for 3 polled mating schemes and compared with baseline selection on lifetime net merit (NM$) alone, over the course of 20 yr. Scenarios were replicated 10 times and the changes in HORNED allele frequency, inbreeding, genetic gain (NM$), and number of unique sires used were calculated. Gene editing decreased the frequency of the HORNED allele to