Inbreeding affects the survival of Danish Jersey and Holstein dairy cows

This study evaluated the effects of pedigree and genomic inbreeding on survival in Danish Jersey (JER) and Danish Holstein (HOL) dairy cows. Survival probabilities and hazard risks (HR) were estimated using Kaplan-Meier analysis and Cox proportional hazards models, with genomic inbreeding quantified through varying lengths of runs of homozygosity (ROH). The results indicated that JER cows had survival probabilities 1.3 to 4 percentage points higher after first calving and throughout later life, along with HR 22 to 29 percentage points lower compared with HOL cows. Both genomic (F_roh) and pedigree inbreeding coefficients increased HR by 1% for each 1% increase in inbreeding. Differences in F_roh based on ROH lengths revealed that longer segments (>10 Mb) increased HR by 2 to 3 percentage points, whereas shorter segments (1-2 Mb) reduced HR by 5 to 7 percentage points. Survival probabilities increased with increasing breeding values. These findings underscore the importance of managing genomic inbreeding to reduce overall culling risks and increase cow survival. Avoiding close inbreeding (ROH >5 Mb) and incorporating genomic relationships into breeding programs can promote the sustainability of dairy systems.