Genetic and environmental risk factors for stillbirth in Japanese Black cattle

Stillbirth is a critical indicator of production efficiency in the beef industry and leads to substantial economic losses. Although the Japanese Black is a premier breed renowned for superior marbling, research on stillbirth risk factors specific to this breed remains limited. This study aimed to identify epidemiological and genetic factors associated with stillbirth in Japanese Black cattle in order to provide actionable insights for production sites. In total, 94,569 calving records from 24,821 cows across 1,001 farms in the Kyushu region (2009-2018) were analyzed using descriptive statistics, a single-trait threshold animal model with Bayesian inference, and mixed-effect model. The overall average stillbirth rate was 1.91%. Small-scale farms exhibited lower stillbirth rates, with more than 70% reporting no stillbirths, whereas large-scale farms showed higher risk, likely reflecting challenges in individual animal observation. Stillbirth rates varied markedly among sires, with some exceeding the overall average by more than 1%. The posterior mean (±SD) estimates for heritability and repeatability were 0.037 ± 0.024 and 0.119 ± 0.040, respectively. Environmental analyses indicated that first-parity cows (odds ratio: 1.858) and winter calving (odds ratio: 1.390) were associated with significantly increased stillbirth risk (P < 0.05). A temporary decline in stillbirth rates was also observed following the 2010 foot-and-mouth disease outbreak, suggesting that reduced herd density and improved care per animal can mitigate risk. Although heritability for stillbirth was low, the relatively high repeatability underscores the importance of managing cows with a prior history of stillbirth. Reducing stillbirth in Japanese Black cattle therefore requires a multifaceted approach, including improved calving management for heifers and winter calvings, use of sire-specific risk information in breeding decisions, and adoption of information and communication technology-based monitoring systems on larger farms. These measures have the potential to reduce economic losses and improve reproductive efficiency.