Suitability of oral administration of monosodium phosphate, disodium phosphate, and magnesium phosphate for the rapid correction of hypophosphatemia in cattle

Background: Hypophosphatemia is commonly associated with disease and decreased productivity in dairy cows particularly in early lactation. Oral supplementation with phosphate salts is recognized as suitable for the rapid correction of hypophosphatemia. Little information is available about the differences in efficacy between salts used for oral phosphorus supplementation. Objectives: Comparison of efficacy of oral administration of NaH₂PO₄, Na₂HPO₄, and MgHPO₄ in treating hypophosphatemia in cattle. Animals: 12 healthy dairy cows in the fourth week of lactation in their second to fifth lactation. Methods: Randomized clinical study. Phosphorus deficient, hypophosphatemic cows underwent a sham treatment and were afterwards assigned to 1 of 3 treatments—NaH₂PO₄, Na₂HPO₄, or MgHPO₄ (each provided the equivalent of 60 g of phosphorus). Blood samples were obtained immediately before and repeatedly after treatment. Results: Treatment with NaH₂PO₄ and Na₂HPO₄ resulted in rapid and sustained increases of plasma phosphate concentrations ([Pi]). Significant effects were apparent within 1 hour (NaH₂PO₄: P =.0044; Na₂HPO₄: P =.0077). Peak increments of plasma [Pi] of 5.33 mg/dL [5.26–5.36] and 4.30 mg/dL [3.59–4.68] (median and interquartile range) were reached after 7 and 6 hours in animals treated with NaPH₂PO₄ and Na₂HPO₄, respectively, whereas treatment with MgHPO₄ led to peak increments 14 hours after treatment (3.19 mg/dL [2.11–4.04]). Conclusions and Clinical Importance: NaH₂PO₄ and Na₂HPO₄ are suitable to rapidly correct hypophosphatemia in cattle. Because of the protracted and weaker effect, MgHPO₄ cannot be recommended for this purpose. Despite important differences in solubility of NaH₂PO₄ and Na₂HPO₄ only small plasma [Pi] differences were observed after treatment.