Risk factors for early and mid-to-late pregnancy loss and their effects on reproductive performance in dairy cows.

importanceThe risk factors and reproductive consequences of pregnancy loss may differ by gestational stage, but stage-specific patterns before and after placentation is firmly established have not been adequately characterized.

objectiveTo identify the risk factors for pregnancy loss at different gestational stages, before and after 60 days of gestation when the placentation is firmly established and quantify the subsequent reproductive performance.

methodsThis study analyzed the records from 6,444 pregnancies confirmed by transrectal ultrasonography 31 days after artificial insemination. Pregnancy loss between 31-61 days was categorized as late embryonic or early fetal loss (LEL-EFL), and losses between 62-260 days were categorized as mid-to-late fetal loss (M-LFL). Multivariable logistic regression was used to assess the risk factors. Survival analysis was performed to assess the probability of becoming pregnant again by 400 days postpartum.

resultsThe cumulative incidence of pregnancy loss was 5.8% for LEL-EFL and 7.7% for M-LFL; LEL-EFL accounted for 43.2% of all losses. A higher body condition score at calving tended to reduce the risk of early loss ( CONCLUSIONS AND RELEVANCE: The patterns of pregnancy loss were stage-specific, and early and later losses had distinct and progressively more adverse effects on reproductive performance. Optimizing the body condition at calving, refining breeding management, and improving peripartum health may reduce pregnancy loss and improve reproductive outcomes.