Risk factors for pregnancy loss across gestational periods in Holstein cattle under a Mexican intensive, temperate...

This study aimed to evaluate whether pregnancy loss during early, mid, or late gestation periods is associated with parity, uterine health, or season of breeding in a Mexican intensive, temperate semi-arid production system. In a retrospective cohort observational study (n = 772), primiparous and multiparous cows with a retained placenta and/or metritis were categorized as having uterine disease (UTD), whereas cows without these conditions were categorized as healthy (HLT). Two seasons of breeding were considered: dry (November-April) and rainy (May-October). Pregnancy loss was classified into three gestation periods: early (33 to 42 days, n = 772), mid (43 to 110 days, n = 706), and late (111 to 202 days, n = 599). Data were analyzed using multivariate logistic regression and Cox proportional hazard regression models. Overall, cows that experienced uterine disease had a higher risk of losing their pregnancy during the early (P = 0.0280), mid (P = 0.0441), and late (P = 0.0340) evaluation periods compared to healthy cows. Concurrently, multiparous cows exhibited a higher risk of pregnancy loss during the mid (P = 0.0048) period compared to primiparous cows. The Cox proportional hazard model indicated that the probability of remaining pregnant over time was consistently lower for UTD cows (P = 0.0010) and multiparous cows (P = 0.0006) compared to their healthy and primiparous counterparts, respectively. In conclusion, postpartum uterine diseases and multiparity are critical risk factors that compromise long-term pregnancy maintenance in dairy cattle managed under intensive, temperate semi-arid production systems in México.