title: Response to genomic selection: the Bulmer effect and the potential of genomic selection when the number of phenotypic records is limiting.
abstract: BACKGROUND
  Over the last ten years, genomic selection has developed enormously. Simulations and results on real data suggest that breeding values can be predicted with high accuracy using genetic markers alone. However, to reach high accuracies, large reference populations are needed. In many livestock populations or even species, such populations cannot be established when traits are difficult or expensive to record, or when the population size is small. The value of genomic selection is then questionable.
  
  
  METHODS
  In this study, we compare traditional breeding schemes based on own performance or progeny information to genomic selection schemes, for which the number of phenotypic records is limiting. Deterministic simulations were performed using selection index theory. Our focus was on the equilibrium response obtained after a few generations of selection. Therefore, we first investigated the magnitude of the Bulmer effect with genomic selection.
  
  
  RESULTS
  Results showed that the reduction in response due to the Bulmer effect is the same for genomic selection as for selection based on traditional BLUP estimated breeding values, and is independent of the accuracy of selection. The reduction in response with genomic selection is greater than with selection based directly on phenotypes without the use of pedigree information, such as mass selection. To maximize the accuracy of genomic estimated breeding values when the number of phenotypic records is limiting, the same individuals should be phenotyped and genotyped, rather than genotyping parents and phenotyping their progeny. When the generation interval cannot be reduced with genomic selection, large reference populations are required to obtain a similar response to that with selection based on BLUP estimated breeding values based on own performance or progeny information. However, when a genomic selection scheme has a moderate decrease in generation interval, relatively small reference population sizes are needed to obtain a similar response to that with selection on traditional BLUP estimated breeding values.
  
  
  CONCLUSIONS
  When the trait of interest cannot be recorded on the selection candidate, genomic selection schemes are very attractive even when the number of phenotypic records is limited, because traditional breeding requires progeny testing schemes with long generation intervals in those cases.
authors.affiliation: Animal Breeding and Genomics Centre, Wageningen University, P,B, 338, Wageningen, The Netherlands.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Van Grevenhof
authors.forename: Johan A M
authors.initials: JA
authors.lastname: Van Arendonk
authors.forename: Piter
authors.initials: P
authors.lastname: Bijma
mesh_terms: D000818:Animals; D001947:Breeding; D005260:Female; D023281:Genomics; D005838:Genotype; D058751:Livestock / Q000235:genetics* / Q000502:physiology; D008297:Male; D008957:Models, Genetic; D010375:Pedigree; D010641:Phenotype; D040641:Quantitative Trait Loci