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The action of the bovine placental lactogen (bPL) hormone on maternal metabolism is still poorly known. Some markers, such as the acute phase protein paraoxonase (PON1), are used as indicators of liver function and help to determine the metabolic condition during the transition period in dairy cows. The aim of this study was to evaluate the activity of paraoxonase (PON1) in the serum of peripartum dairy cows with different levels of bPL. Based on the plasma bPL concentration, 18 cows were divided equally into three groups: LOW ( < 2,68 ng bPL mL-1), MEDIUM (2,68–2,80 ng bPL mL-1), and HIGH ( > 2,80 ng bPL mL-1). The experiment was conducted between 21 days prepartum and 28 days postpartum. Serum samples were collected during the experiment for the determination of bPL concentrations and PON1 activity. The bPL concentration was significantly different between the experimental groups (P ? 0,0001) and the days of serum collection (P ? 0,0001). In the prepartum dairy cows, the PON1 levels were different between the groups (P ? 0,05) and the days of serum collection (P ? 0,05). Cows with high bPL concentration had lower serum PON1 activity (P ? 0,05), while cows with low hormone levels had higher enzyme activity (P ? 0,05). In the postpartum period, there was a significant difference between the days of serum collection (P ? 0,0001) and the interaction between groups and collections (P ? 0,01). The group with high concentrations of bPL had lower levels of PON1 (P ? 0,01), while the group with low bPL maintained higher concentrations of PON1 (P ? 0,01). It was concluded that the cows with higher concentrations of bPL in the prepartum period present a reduction in the serum activity of the PON1 enzyme during the peripartum period.