Fractional excretion of electrolytes during pre- and postpartum periods in cows

In this study, fractional excretions (Fe) of sodium (Na), potassium (K), chloride (Cl), calcium (Ca), magnesium (Mg) and phosphorus (PO4) were examined with the aim to demonstrate interactions between fractional excretions of these electrolytes within each period and relate them to electrolyte metabolism in clinically normal cows at different stages of lactation and dry period. The material of this study consisted of 20 clinically healthy Holstein-Friesian cows of the same age and milk yield. Blood and urine samples were collected on 190-200th, 240-250th and 270-280th days of pregnancy and on days 1-7th, 35-45th and 75-85th after calving, altogether 6 times. An increase was observed in FeCa and FeMg during the transition from the lactation to the dry period (p < 0.05), and a decrease in FeCa (p < 0.05), FeMg (p < 0.01) in the 2nd month of the dry period. FePO4 and FeMg, respectively, increased on levels of p < 0.01 and p < 0.05, while FeCa decreased on a level of p < 0.05 after gestation compared to the level before gestation. FeNa and FeK showed a decrease of p < 0.001 and p < 0.01, respectively, between the 1st and 2nd months of the dry period, while after gestation this value showed an increase in FeNa (p < 0.05) and FeK (p < 0.01). FeCl increased significantly (p < 0.05) only from postpartum to the 1st month of lactation. There was a strong positive correlation between FeNa and FeCl in all of the periods. It was concluded that there were significant changes in the Fe of Na, K, Cl, Ca, PO4 and Mg before parturition and during lactation; these changes could have an important role in assessing renal function and electrolyte balance.