Elevated non-esterified fatty acid and β-hydroxybutyrate in transition dairy cows and their association with reproductive performance and disorders: A meta-analysis

- Overview on the association between high BHBA or NEFA and reproductive performance.
- Failure to conclude on the association between estrus cyclicity and high BHBA or NEFA.
- Need of further epidemiologic studies on this topic.

A meta-analysis including 36 different results of statistic models from 14 papers was conducted. It evaluated the association between elevated non-esterified fatty acids and/or β-hydroxybutyrate (BHB) on the reproduction outcomes that were pregnancy at first insemination, estrous cyclicity, time to pregnancy, metritis and placental retention. Each association between BHB or NEFA and an outcome reported in literature was a model considered as raw-data for the meta-regression. For each outcome, the meta-regression adjusted the odds ratio, relative risk or hazard ratio with various moderators to reduce the heterogeneity among the studies. The relative risk for metritis and placental retention in case of high BHB or NEFA was in accordance to previous meta-regression and was 1.91 (IC95 = 1.72 to 2.12) and 1.51 (95%CI = 1.19 to 1.92), respectively. The relative risk for pregnancy at first insemination in case of high BHB was assessed to be 0,62 (95%CI = 0,41 to 0,93). The hazard ratio for time to pregnancy in case of high BHB and NEFA was 0.77 (95%CI = 0.61 to 0.97). The present meta-analysis failed to clearly conclude on the association between estrus cyclicity and high BHB or NEFA. The present work allowed a new overview on the association between hyperketonemia and reproductive performance and disorders. It updated the previous meta-regression and included new outcomes. It highlighted the urgent need of further intensive epidemiologic studies on this topic.