Does the choice of beef bull influence dairy cow survival in a beef × dairy system?

The increasing use of beef sires in dairy herds, largely enabled by reproductive technologies such as sexed semen, has created new dynamics in dairy production, including a surplus of replacement heifers. This has driven widespread adoption of beef × dairy breeding strategies to reduce the surplus of dairy heifers and increase meat output without compromising milk production. However, this practice introduces new challenges, particularly concerning dairy cow survival. A key concern is whether dairy cows inseminated with beef semen experience higher mortality, and if so, whether this can be addressed through genetic selection on the paternal side. Genetic variation was investigated among 223 Danish Blue sires used on 145,513 Holstein cows, covering 209,523 multiparous calvings. The focus is on cow survival at d 50 post-calving (SURV50), alongside survival to next lactation. A bivariate model of these survival traits and a 4-trait multivariate model (calving ease, calf survival at birth, calf size, SURV50) was examined. Both models included fixed effects (herd-year, year-month, calf sex, parity, cow age at calving nested within parity) along with random additive genetic effect of sire. Results revealed a significant additive genetic sire variation with a low heritability (<0.01), high genetic correlation (0.92; SE: 0.22) between survival traits, and a moderate favorable genetic correlation between SURV50 and calving ease (-0.65 ± 0.30). Furthermore, SURV50 can be defined as a genetic residual SURV50 trait that is genetically independent of the aforementioned calving traits (gSURV50). For the residual gSURV50 trait, 57% of the additive genetic sire variation remained of the SURV50 trait, suggesting that early-lactation survival of dairy cows inseminated with beef semen is not solely affected by calving-related traits. Effectively, that means selection on gSURV50 targets early lactation dairy cow survival effects beyond calving outcomes. Using simulated profitability estimates, one genetic standard deviation improvement in gSURV50 corresponded to €6.25, which potentially could contribute substantially to the Nordic breeding goal for beef sires used on dairy cows. Overall, the results of this study demonstrate additive genetic sire variation in dairy cow survival among Danish Blue sires under Danish production conditions. Incorporating gSURV50 into beef × dairy breeding objectives, could potentially enhance robustness, reduce mortality, and improve both animal welfare and economic efficiency.