Single-step GBLUP evaluation for categorical traits for beef cattle

In order to study the performance of single-step genomic prediction for a categorical trait such as calving difficulty in beef cattle, data was simulated and single-step genomic breeding values (GEBV) and pedigree-based breeding values (PEBV) were estimated. Different number of trait categories with and without normal score transformation, and including different information sources, were studied. For a trait with a heritability of 0.30 and four categories, the increase in accuracy using GEBV compared with PEBV was 28.6% with, and 27.9% without normal score transformation, respectively. Moreover, in a scenario without phenotypes for males, the accuracy of GEBV was 26.6% higher than for PEBV for a binary trait with a heritability of 0.05. All results indicated that single-step genomic evaluation of categorical traits is beneficial to use in beef cattle breeding programs.