Nordic genomic prediction for crossbred dairy females
Genomic predictions have been applied in dairy cattle for more than a decade with great success, but genomic estimated breeding values (GEBV) are not widely available for crossbred dairy females. In the Nordic countries NAV have implemented GEBV for female crosses between Holstein, RDC and Jersey. A breed of origin model (BOM) exploiting breed origin of the alleles (BOA) has been chosen, where SNP solutions from genomic prediction in the three pure breeds are utilized. Genotypes are imputed and phased using FImpute. Assignment to breed of origin is done by the AllOr program. GEBVs are calculated for the same main traits as purebred animals. Estimation of GEBVs for cross breeds include the following steps: 1) Express the SNP solutions from official pure breed genomic evaluations to phenotypic scale. 2) calculate direct genomic value (DGV) by multiplying genotypes by purebred SNP solutions considering BOA. 3) Rescale the polygenic effect from genotyped purebred ancestors to phenotypic scale if available 4) calculate polygenic effect for each animal. 5) Calculate GEBV from DGV and polygenic effect considering the genetic difference between breeds. 6) Combine breeding values for main trait groups in a total merit index (NTM). 7) Standardize GEBVs to an average of 0 for NTM and 100 for all other traits for animals in the base population. Animals in the defined genetic base population are genotyped crossbred females of 1 to 7 years of age at the publication date. Implementation of GEBVs for crossbred females in the Nordic countries give farmers the same opportunities to do within herd selection of their genomic tested crossbred heifers as of purebred heifers. Hence, this will be an important strategic tool at herd level to optimize the use of sexed semen and beef semen
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