Genetic correlations between juvenile mortality traits and traits in selection on French dairy cattle breeds

Abstract

Reducing juvenile mortality is a pressing challenge for the dairy cattle industry due to its economic, environmental, and animal welfare impacts. While juvenile mortality has multiple causes, genetics plays a substantial role. The implementation of a routine genomic evaluation could therefore contribute to achieving this goal. In France, a genomic evaluation for mortality within the first 48 hours of life is already available for dairy cattle breeds. As part of the SEVITAL project, new juvenile mortality traits covering the first year of life are being studied for inclusion, in the breeding programs of nine dairy breeds (Abondance, Brown Swiss, Holstein, Jersey, Montbéliarde, Normande, Simmental, Tarentaise and Vosgienne). Life history information, i.e. date of birth, date and cause of death (natural death or slaughter) were extracted from the French national cattle database for females born from 2010 to 2024. Three traits have been defined based on the age at which the animal died: 3-30 days, when the leading cause of calf mortality is diarrhea; 31-365 days, when calf mortality is mainly due to respiratory diseases; 3-365 days, to cover the whole period. These traits were defined as binary traits: 0 was assigned to animals still alive during the considered period, and a value of 100 was assigned to animals that died. For each trait, single-step genomic evaluations were carried out with HSSGBLUP (Tribout et al., 2020) using a univariate animal model that included herd x year-of-birth and region x month-of-birth x year-of-birth as fixed effects. Estimated breeding values (EBVs) of bulls were calculated using the performances of a total number of 4,750 to 2,236,362 animals depending on the breed, among which 2,683 to 608,585 were genotyped. Correlations between juvenile mortality traits and traits routinely evaluated (milk production traits, udder health, fertility, mortality within the first 48 hours) were estimated using Calo’s method (Calo et al., 1973). The correlations between EBVs adjusted for their reliability estimated with this method provided an approximation of the genetic correlations. By offering a better understanding of the genetic relationships between traits, these results will help breeding companies determine how to incorporate juvenile mortality traits in their overall breeding objectives.