Genetic variation in novel calf traits using a farmer-centered, co-design approach to data collection

Improving calf health on dairy farms contributes to animal welfare and business productivity gains. In recent years, traditional genetic evaluations have broadened to include cow health traits that have economic importance. Calf health is a new frontier to explore, but new traits require sufficient data to be effectively evaluated. Researchers who work in countries without obligatory recordkeeping systems, commonly promote the need to significantly improve recordkeeping practices to enable research, benchmarking, and genetic evaluation, as is the case in Australia. The aim of this study was to estimate variance components for novel calf traits using a dataset that was co-designed with farmers and included calf identity, calving ease, health records, and genotypes. Almost 20,000 calf records from more than 50 farms located throughout Australia were collected between 2020 and 2023. In Holstein calves, the mean ± SE prevalence of preweaning mortality (PWM) and scours, were 0.020 ± 0.001 and 0.059 ± 0.002, respectively. A newly defined and subjectively scored trait called calf vitality was co-developed with farmers, where 21% of calves were classed in the top category of vigorous or "ripper," 54% were good or average, 6% were "duds," and 19% of scored calves died. Univariate linear models that included a genomic relationship matrix were used to estimate variance components for diseases and vitality, where h² values were between 1% and 11% in Holsteins, depending on the trait. The models included herd-year-season, sex, parity group, and calving ease (Holstein only) as fixed effects and these were found to be significant for most breed and trait combinations. The estimated reliability of EBVs ranged between 0.2 and 0.3. In Australia, Holsteins are more numerous than the Jersey breed, and so despite efforts to compile an appropriate dataset, the disease prevalence and record numbers were too low to report genetic variance for calf health traits in the Jersey breed. Approximate genetic correlations with other calf health traits such as stillbirth and PWM were modest but favorable. There were few significant correlations with lactating cow traits (such as survival, SCC, and likeability) and national selection indexes that are routinely evaluated in Australia and those that were significant were in a favorable direction.