engleski

Serum paraoxonase activity in dairy cows during early postpartum period

Paraoxonase (EC 3.1.8.1) is calcium-dependent esterase that catalyses hydrolysis of organophosphates. In serum it is associated with high density lipoproteins (HDL) and involved in the antioxidant protection based on hydrolysis of lipid hydroperoxides on low density lipoproteins (LDL). The period of transition from late pregnancy to early lactation in high-yielding dairy cows presents an increase in requirements for energy, what is often associated with lipid metabolism disorders. In such conditions of energy deficit changes of oxidative status is to be expected, so we investigated the serum paraoxonase activity in dairy cows during early postpartum period. 21 Holstein dairy cows in early postpartum period (app. 10-15 days after calving) and 19 non-pregnant Simental and Holstein dairy cows in late lactation were investigated. In collected sera concentrations of triglyceride, cholesterol and HDL-cholesterol were determined using enzymatic kit methods (Herbos Diagnostics, Sisak, Croatia). Basal paraoxonase activity was determined by measuring the hydroysis of paraoxon (2, 0 mM) at 37°C on a Technicon RA-1000 autoanalyzer, while salt-stimulated paraoxonase activity was performed by the same method with 1 M NaCl added. In sera of cows in early postpartum period the mean cholesterol and triglyceride concentrations (2, 38 mmol/L and 0, 08 mmol/L, respectively) were significantly lower than in sera of cows in late lactation (4, 94 mmol/L and 0, 23 mmol/L, respectively). Serum HDL-cholesterol concentration was not significantly different between these two groups (1, 22 mmol/L:1, 16 mmol/L). Serum basal paraoxonase activity (315 U/L) and salt-stimulated activity (450 U/L) in cows in early postpartum period were significantly lower than in cows in late lactation (486 U/L:748 U/L). The percent of salt-stimulation paraoxonase activity was also significantly different between two groups. Serum basal and stimulated paraoxonase activity in cows in early postpartum period expressed on mmol/L HDL-cholesterol (283 U/mmol HDL and 404 U/mmol HDL, respectively) were significantly lower than in cows in late lactation (459 U/mmol HDL and 710 U/mmol HDL, respectively). Obtained results indicate that lower serum paraoxonase activity in early postpartum period is due to metabolic and energy disorders caused by energy deficit. We can concluded that lower serum paraoxonase activity suggesting intensive oxidative changes and oxidative stress development during the energy deficiency.

paraoxonase; dairy cows; postpartum

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