Abstract #463

# 463
Validation of genomic predictions for linear type traits in US Holsteins using over 2 million genotyped animals.
S. Tsuruta*1, D. A. L. Lourenco1, Y. Masuda1, I. Misztal1, T. J. Lawlor2, 1University of Georgia, Athens, GA, 2Holstein Association USA, Brattleboro, VT.

As accumulating more genotypes, the validation of genomic predictions can be more reliable. In our previous studies, 0.5 million genotyped Holsteins were used to predict genomic (G)PTA. Today, genotypes for over 2 million Holsteins are available, meaning that more genotyped young animals can be used for validation. The objective of this study was to investigate biases in GPTA for young genotyped bulls and verify that the method with a single-step genomic BLUP that has been used in our studies is reliable. Phenotypes for 18 linear type traits used in 2018 genetic evaluation were provided by Holstein Association USA, and genotypes in 2018 were provided by the Council on Dairy Cattle Breeding. The full data set consisted of 10,946,264 records up to 2018 calving, 13,591,145 animals in the pedigree, and 2,334,951 genotyped animals with 80K SNP. Young genotyped bulls with no daughters in 2014 and with at least 50 daughters in 2018 were used to calculate regression coefficients (b1) of GPTA in 2014 on daughter yield deviations in 2018 as an indicator of inflation or deflation of GPTA. Coefficients of determination (R2) were used to compare accuracies in parent averages and GPTA. The BLUP90IOD2 program was used to predict GPTA in 2014 and in 2018 with the single-step genomic BLUP using the algorithm of proven and young animals. Genetic trends were also calculated to detect the bias in GPTA. All results from this study were compared with the results from our previous study that used phenotypes and genotypes as of 2014. The model included inbreeding in the pedigree-based relationships and estimable unknown parent groups to reduce inflation and minimize biases in GPTA as suggested in our previous studies. Inflation or deflation (b1) in GTPA was within 1.0 ± 0.1 on average, depending on the trait, but more stable than the previous results. Genetic trends verified that the model used in this study was unbiased. More young genotyped bulls could provide more stable and reliable results for the validation of GPTA. Convergence via BLUP90IOD2 was reached in 3 d using >300GB memory. The program can be optimized to accelerate the computing speed in the near future.

Key Words: single-step genomic BLUP, linear type trait, US Holsteins