International genomic evaluation methods for dairy cattle

Paul M Vanraden,Peter G Sullivan

doi:10.1186/1297-9686-42-7

Abstract

BackgroundGenomic evaluations are rapidly replacing traditional evaluation systems used for dairy cattle selection. Higher reliabilities from larger genotype files promote cooperation across country borders. Genomic information can be exchanged across countries using simple conversion equations, by modifying multi-trait across-country evaluation (MACE) to account for correlated residuals originating from the use of foreign evaluations, or by multi-trait analysis of genotypes for countries that use the same reference animals.MethodsTraditional MACE assumes independent residuals because each daughter is measured in only one country. Genomic MACE could account for residual correlations using daughter equivalents from genomic data as a fraction of the total in each country and proportions of bulls shared. MACE methods developed to combine separate within-country genomic evaluations were compared to direct, multi-country analysis of combined genotypes using simulated genomic and phenotypic data for 8,193 bulls in nine countries.ResultsReliabilities for young bulls were much higher for across-country than within-country genomic evaluations as measured by squared correlations of estimated with true breeding values. Gains in reliability from genomic MACE were similar to those of multi-trait evaluation of genotypes but required less computation. Sharing of reference genotypes among countries created large residual correlations, especially for young bulls, that are accounted for in genomic MACE.ConclusionsInternational genomic evaluations can be computed either by modifying MACE to account for residual correlations across countries or by multi-trait evaluation of combined genotype files. The gains in reliability justify the increased computation but require more cooperation than in previous breeding programs.

Highlights

Genomic evaluations are rapidly replacing traditional evaluation systems used for dairy cattle selection
Deregressed estimated breeding value (EBV) are recommended as the y variable in genomic evaluations [6]
Comparison of evaluation systems Reliability of selection for young animals greatly increased when national and international genomic evaluation models were applied to simulated data

Summary

Introduction

Genomic evaluations are rapidly replacing traditional evaluation systems used for dairy cattle selection. Genomic information can be exchanged across countries using simple conversion equations, by modifying multi-trait acrosscountry evaluation (MACE) to account for correlated residuals originating from the use of foreign evaluations, or by multi-trait analysis of genotypes for countries that use the same reference animals. Selection in many countries uses genotypes in addition to phenotypes and pedigrees [1,2]. Changes from genetic to genomic evaluations for dairy cattle at the national level will require corresponding changes to international evaluations. Phenotypes are collected, stored, and evaluated independently by each country, and the resulting estimated breeding value (EBV) files are exchanged and combined by Interbull. New methods are needed to exchange and combine genomic EBV (GEBV) files that include young bulls and perhaps females

Objectives

Methods

Results

Discussion

Conclusion