Young AE, Mansour TA, McNabb BR, Owen JR, Trott JF, Brown CT, Van Eenennaam AL
Genome editing followed by reproductive cloning was previously used to produce two hornless dairy bulls. We crossed one genome-edited dairy bull, homozygous for the dominant P Celtic POLLED allele, with horned cows (pp) and obtained six heterozygous (Pp) polled calves. The calves had no horns and were otherwise healthy and phenotypically unremarkable. We conducted whole-genome sequencing of all animals using an Illumina HiSeq4000 to achieve ~20× coverage. Bioinformatics analyses revealed the bull was a compound heterozygote, carrying one naturally occurring P Celtic POLLED allele and an allele containing an additional introgression of the homology-directed repair donor plasmid along with the P Celtic allele. These alleles segregated in the offspring of this bull, and inheritance of either allele produced polled calves. No other unintended genomic alterations were observed. These data can be used to inform conversations in the scientific community, with regulatory authorities and with the public around 'intentional genomic alterations' and future regulatory actions regarding genome-edited animals.