Comparative efficacy of five calcium and phosphorus treatment protocols in puerperal hypocalcemia and relapse prevention.

Adjunctive oral calcium or parenteral phosphorus provides no additional benefit over IV calcium alone for milk fever.

This prospective randomized study evaluated five calcium and phosphorus treatment protocols in 41 postpartum dairy cows diagnosed with milk fever (puerperal hypocalcemia). All cows received intravenous calcium as the foundation therapy, with some groups receiving adjunctive treatments including oral calcium pidolate, oral calcium chloride boluses, liquid oral calcium, or parenteral toldimfos (a phosphorus supplement). Plasma concentrations of calcium, phosphorus, magnesium, parathyroid hormone (PTH), and calcitriol were measured at baseline and serially up to 96 hours post-infusion. Clinical endpoints included time to standing, relapse rate, and alert downer status. All 41 cows achieved standing following treatment; however, nine cows relapsed and two required euthanasia due to persistent recumbency. No adjunctive therapy demonstrated superior clinical or biochemical outcomes compared with intravenous calcium alone, which restored normocalcemia for approximately 8 hours. Notably, pre-treatment calcitriol concentrations were significantly lower in cows that subsequently relapsed, suggesting impaired vitamin D–calcium axis activation as a contributing factor. Pre-treatment blood calcium was lower in single-relapse cows but paradoxically higher in alert downers. At 24 hours, both calcium and phosphorus were lower in single-relapse cows, while only phosphorus was reduced in multiple-relapse cows. The authors conclude that milk fever relapse appears more closely associated with disrupted calcium–vitamin D metabolism than with phosphorus deficiency alone, and that current adjunctive phosphorus or oral calcium therapies offer no proven advantage over intravenous calcium monotherapy.

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