Measuring Genomic Pre-Selection in Theory and in Practice


  • Paul M VanRaden USDA Animal Improvement Programs Lab
  • Janice R Wright USDA Animal Improvement Programs Lab


genomic evaluation, information sources, pre-selection bias, single-step model


Potential biases from genomic pre-selection were estimated from actual selection and mating patterns of US Holsteins. Traditional models using only phenotypes and pedigrees do not adjust for average genomic merit of an animal’s parents, progeny, mates, or contemporaries. Positive assortative mating of elite young bulls to elite genotyped females and dams of highly selected sons will become primary sources of bias in the next few years unless methods of adjustment are introduced. However, deregression can remove some biases such as by crediting the dam for only her own records andnot for those of her selected progeny. Diagonals of genomic and pedigree relationship matrices, their inverses, and their differences were examined. The animal’s own genotype provides a fourth source of information along with traditional information from parents, progeny, and own phenotype.

Author Biographies

Paul M VanRaden, USDA Animal Improvement Programs Lab

Research geneticist

Janice R Wright, USDA Animal Improvement Programs Lab

Animal scientist