title: A common reference population from four European Holstein populations increases reliability of genomic predictions.
abstract: BACKGROUND
  Size of the reference population and reliability of phenotypes are crucial factors influencing the reliability of genomic predictions. It is therefore useful to combine closely related populations. Increased accuracies of genomic predictions depend on the number of individuals added to the reference population, the reliability of their phenotypes, and the relatedness of the populations that are combined.
  
  
  METHODS
  This paper assesses the increase in reliability achieved when combining four Holstein reference populations of 4000 bulls each, from European breeding organizations, i.e. UNCEIA (France), VikingGenetics (Denmark, Sweden, Finland), DHV-VIT (Germany) and CRV (The Netherlands, Flanders). Each partner validated its own bulls using their national reference data and the combined data, respectively.
  
  
  RESULTS
  Combining the data significantly increased the reliability of genomic predictions for bulls in all four populations. Reliabilities increased by 10%, compared to reliabilities obtained with national reference populations alone, when they were averaged over countries and the traits evaluated. For different traits and countries, the increase in reliability ranged from 2% to 19%.
  
  
  CONCLUSIONS
  Genomic selection programs benefit greatly from combining data from several closely related populations into a single large reference population.
authors.affiliation: Department of Molecular Biology and Genetics, Faculty of Science and Technology, Aarhus University, AU-Foulum, PO Box 50, DK-8830 Tjele, Denmark. Mogens.Lund@agrsci.dk
authors.forename: Mogens S
authors.initials: MS
authors.lastname: Lund
authors.forename: Adrianus P W de
authors.initials: AP
authors.lastname: Roos
authors.forename: Alfred G de
authors.initials: AG
authors.lastname: Vries
authors.forename: Tom
authors.initials: T
authors.lastname: Druet
authors.forename: Vincent
authors.initials: V
authors.lastname: Ducrocq
authors.forename: Sébastien
authors.initials: S
authors.lastname: Fritz
authors.forename: François
authors.initials: F
authors.lastname: Guillaume
authors.forename: Bernt
authors.initials: B
authors.lastname: Guldbrandtsen
authors.forename: Zenting
authors.initials: Z
authors.lastname: Liu
authors.forename: Reinhard
authors.initials: R
authors.lastname: Reents
authors.forename: Chris
authors.initials: C
authors.lastname: Schrooten
authors.forename: Franz
authors.initials: F
authors.lastname: Seefried
authors.forename: Guosheng
authors.initials: G
authors.lastname: Su
mesh_terms: D000818:Animals; D001947:Breeding; D002417:Cattle; D005060:Europe; D005260:Female; D014644:Genetic Variation; D008297:Male; D008957:Models, Genetic; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D040641:Quantitative Trait Loci; D012016:Reference Values; D012641:Selection, Genetic