Managing lethal alleles using genomic optimum contribution selection Line Hjortø Jørn Rind Thomasen Peer Berg Morten Kargo Mark Henryon Huiming Liu Christian Sørensen

Hypotheses Culling carriers of recessive lethals reduce genetic gain obtained from truncation selection Optimum-Contribution Selection reduces frequency of recessive lethal without compromising genetic gain

Design Selection Culling of carriers Truncation OCS with pedigree OCS with G-matrix Culling of carriers None Male carriers Female carriers All carriers

Genetic Models Frequency of recessive lethal allele 0.05, 0.10, or 0.15 Effect on Breeding Goal 0 or 3% of VA explained by lethal Linked to other QTLs Yes or No

at the same rate of true inbreeding, IBD Criterion Genetic gain at the same rate of true inbreeding, IBD Assessed the two constraints by rate of genetic gain per rate of true inbreeding. Rate of genetic gain was measured as average true breeding value. Rate of true inbreeding was measured as proportion of homozygosity at unique

Relative initial genetic gain Truncation OCS - ped OCS - gen No culling 100% 102% 99% All carriers culled 81% 104% Male carriers culled 93% 97% Female carriers culled 88% 98% Large interaction exist

Relative long-term genetic gain Truncation OCS - ped OCS - gen No culling 100% 112% All carriers culled 113% Male carriers culled Female carriers culled 101% No interaction

At the same rate of true inbreeding Truncation 61 sires OCS using pedigree 35 sires OCS using genomic information 32 sires OCS selects stronger within families, while truncation selects more males to cover enough families

Frequency of lethal allele OCS - gen OCS - ped Truncation Generation

Summary Carrier culling reduces initial genetic gain of truncation selection Carrier culling of a single lethal does not affect long-term genetic gain OCS tend to slow natural selection against lethal OCS tidy up the mess from carrier culling

OCS should be used, when carriers are culled in a pre-selection step Conclusion OCS should be used, when carriers are culled in a pre-selection step