Using Australian genomics to predict dairy cattle performance in New Zealand

Context: The national breeding objective in New Zealand (NZ) was designed with the intention to breed dairy cows that efficiently convert feed into profit. The breeding worth index (BW) is used to rank bulls and cows according to their ability to meet this objective. The Australian equivalent to BW is the balanced performance index (BPI). These selection indexes represent national economic weights for important traits in dairy industry in each country. The introduction of Australian genomics has allowed the selection and ranking of young sires from around the world on BPI. Aims: This study aims to demonstrate the relationship between different traits and selection indexes in Australia (AU) and NZ by comparing sires with daughter proofs in both countries and the validity of predicting BW for NZ sires using Australian genomic predictions and regression equations. Methods: Data files for sires with daughters in both AU and NZ were merged to identify common bulls used in both countries. An analysis was conducted to determine whether Australian breeding values (ABVs) for sires could be used to predict the performance of the sires that have no progeny in NZ. ABVs for nine traits in BW were converted to their equivalent NZ breeding values (NBVs) and used to calculate an index equivalent to BW. Key results: On the basis of a regression equation, a new index called genomic New Zealand index (gNZI) for selecting sires for NZ dairy herds was developed. The correlation coefficients between gNZI and BW in Holstein Friesian (HF), Jersey, and Red breeds were 0.90, 0.91, and 0.88 respectively. Conclusions: The regression equation from genomic ABVs to produce gNZI was a reliable genomic predictor of future BW for sires with insufficient ancestry information in NZ and to enhance the ancestry proofs and increase the reliability of selecting young NZ-born bulls. Implications: The high correlations between traits in AU and NZ and the simple proposed conversion method can build industry confidence when selecting young bulls using gNZI, as genomic prediction of BW through New Zealand Animal Evaluation (NZAEL) is not currently available.