Validation of calving ease EBVs examining the impact of genetic groups and single-step on predictive ability

Calving difficulty scores recorded in beef cattle are challenging to analyse due to low frequency of difficult births and the scored nature of the trait, requiring analysis in a threshold model, typically in combination with two linear traits, birth weight and gestation length. Previous software to calculate estimated breeding values (EBVs) for calving ease was not able to include single-step methods or fit genetic groups in models of analysis. In this study, we examined the value of including genetic groups and genomic information via single-step genomic BLUP (ssGBLUP) in the TransTasman Angus Cattle Evaluation (TACE) BREEDPLAN and Hereford BREEDPLAN analyses, by forward-validation in genotyped animals. The greatest improvements in accuracy were observed when including genomic information, with increases of 0.169 and 0.106 in the Angus and Hereford analyses respectively. Adding genetic groups to models had no impact on accuracy, but increased the bias of CE EBVs in ssGBLUP analyses for both breeds.