Background: High concentrations of NEFA relative to a defined reference or ‘cut-point’ values before calving can predict the risk of specific or collective periparturient disease events. Objectives: A field-based cohort study was conducted to evaluate the value and critical points of serum nonesterified fatty acids (NEFA) at the precalving time to predict the occurrence of postpartum diseases and reproductive performance in dairy cows. Methods: Blood samples were taken from 521 high-yielding dairy cows at 1 week (±3 days) before calving and NEFA levels were measured. Health and reproduction information of each cow includes dystocia, retained placenta, milk fever, metritis, mas- titis, pregnancy in the first insemination and pregnancy in the first two inseminations, and culling in the first 60 days of lactation and milk production. Results: Our results show that there are significant relationships between precalving NEFA with the probability of pregnancy at the first and the first two inseminations after calving. The cows that had NEFA concentrations less than 0.5 mmol/L at the last week of pregnancy were 3.51 and 3.15 times more likely to be pregnant at first insemination and the first two inseminations, respectively. Also, our results showed that there are significant relationships between precalving NEFA concentration and the likelihood of dystocia and milk fever. The probability of dystocia and milk fever occurrence were 2.56 and 1.91 times greater in those cows that had NEFA concentrations more than 0.3 mmol/L, respectively. Conclusions: The present results indicated that Increasing NEFA during the prepartum period could adversely affect the reproductive efficiency of dairy cows.

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