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

Abstract

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 record keeping systems, commonly promote the need to significantly improve record keeping 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 data set that was co-designed with farmers and included calf identity, calving ease, health records and genotypes. Almost 20,000 calf records from over 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 (vitality) was co-developed with farmers, where 21% of calves were classed in the top category of ripper/vigorous, while 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 heritability values were between 1% and 11% in Holsteins depending on the trait. The models included herd-year-season (HYS), sex, parity group and calving ease (Holstein only) as fixed effects and these were found to be significant (P < 0.05 to 0.001) 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 data set, 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 (SB) and PWM were modest but favorable. There were few significant correlations with lactating cow traits (such as survival, somatic cell count and likeability) and national selection indexes that are routinely evaluated in Australia and those that were significant were in a favorable direction.