Adding and reporting genomically discovered ancestors in US evaluations

Abstract

Unknown maternal grandsires (MGS) and great grandsires (MGGS) can be discovered accurately based upon haplotype matching. The Council on Dairy Cattle Breeding (CDCB) has already added about 370,000 discovered MGS to dams with unknown sire where no pedigree was submitted for the dam and 30,000 discovered MGGS where no pedigree was submitted for the maternal granddam (MGD). To add MGS or MGGS to the pedigree, where the dam or MGD is unknown, requires creating an ID for the dam or granddam. These constructed IDs consist of the breed of the discovered MGS or MGGS as the best guess of the unknown dam breed, the ‘USA’ code, the letters ‘DAM’ or ‘MGD’ followed by the genotyped animal internal sequence number. For about 30,000 cases, a calf’s non-genotyped dam can be discovered by finding a cow in the same herd whose sire is the discovered MGS and has a calving date that matches the calf’s birth date. CDCB plans to add > 1 million more discovered MGS and MGGS linked to their genotyped descendants by constructed IDs to the national pedigree in 2022. Accuracy was tested from 2021 data by randomly removing genotypes and pedigrees for dams and MGD with confirmed sires to determine how often the correct MGS and MGGS could be discovered. Within each breed about 92% of true grandsires were automatically filled correctly, about 5% of true grandsires were suggested but not filled, and < 2% of the added ancestors were incorrect. Updated edits further improved accuracy. Discovered ancestors thought to be incorrect can be set back to missing by animal owners. More complete pedigrees will help breeders to avoid inbreeding and improve evaluation accuracy.