Effect of rapid intravenous administration of 50% dextrose solution on phosphorus homeostasis in postparturient dairy cows

BACKGROUND: Dextrose is commonly administered to postparturient dairy cows, which often have low plasma phosphorus concentration ([P]) as a result of anorexia and sudden onset of lactation. Intravenous (IV) dextrose administration causes hypophosphatemia in other species.

HYPOTHESIS: Bolus administration of dextrose to postparturient dairy cows results in a transient decrease in plasma [P].

ANIMALS: Six healthy postparturient dairy cows.

METHODS: Using a crossover design, cows were administered 500 mL of 50% dextrose solution IV or a sham treatment. Plasma concentrations of glucose ([glucose]), immunoreactive insulin ([IRI]), and phosphorus were monitored for 12 hours after each treatment. Urine [P], [glucose], and volume and salivary [P] were also determined.

RESULTS: Plasma [glucose], [IRI], and [P] were stable during sham treatment. Plasma [P] decreased rapidly after dextrose administration, dropping by 35% in 1 hour and remaining below baseline for 90 minutes. Salivary [P], urine [P], and urine volume per hour remained stable after dextrose administration, but glucose was detected in urine for up to 6 hours. The amount of glucose excreted in urine in 12 hours (11.9+/-4.5 g) was less than 5% of the administered dose. Regression analysis revealed a stronger association between plasma [P] and [IRI] than between plasma [P] and [glucose], suggesting that hyperinsulinemia drove the hypophosphatemia.

CONCLUSION AND CLINICAL IMPORTANCE: Results indicate that low plasma [P] should be expected in cows that have received IV dextrose within 1 hour before blood sampling. Caution is advised when administering dextrose solution to cows already at risk of hypophosphatemia.