Retained placenta in dairy cows: An evaluation of risk factors and reproductive performance

Retained placenta (RP) is a common postpartum disorder in dairy cows and is consistently associated with impaired fertility and increased reproductive losses. This study aimed to identify environmental, management, and genetic factors associated with RP and to evaluate its effects on reproductive performance and culling in commercial dairy farms under tropical conditions. A retrospective dataset including 138,175 calvings from 437 commercial dairy herds after data validation, from 2021 to 2023 was analyzed. Retained placenta was defined as the failure to expel the fetal membranes within 24 h after calving. Generalized linear mixed models were fitted using the glmmTMB package in R, with farm and cow included as random effects when appropriate. A total of 289,391 artificial insemination (AI) records were available for pregnancy per AI (P/AI) analyses, and 57,628 confirmed pregnancies were used for pregnancy loss (PL) analyses. Fixed effects included parity, breed, type of artificial insemination (AI), season, and year. Farms had Holstein and Holstein × Gyr (HG) crossbred cows in free stall, compost barn, or dry lot systems. Twin births, male calves, abortions, premature, higher parity, and the Holstein breed were associated with increased odds of RP. Crossbred 1/2 Holstein × Gyr (HG) cows had lower odds of RP compared to Holstein cows. Retained placenta was associated with reduced odds of P/AI at first and overall inseminations and with increased odds for PL, consistently across breeds, parity groups, and AI strategies. Cows affected by RP also had a higher risk of culling during lactation. These findings highlight the multifactorial nature of RP and its persistent negative association with fertility and herd longevity in tropical dairy systems.