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

Intravenous calcium is the standard treatment for milk fever, although adjunctive therapies such as oral calcium or parenteral phosphorus are often used, with unclear additional benefits. This study evaluated whether adjunctive calcium or phosphorus therapies improve clinical and biochemical recovery following intravenous calcium treatment. This prospective study included 41 postpartum cows with milk fever randomly assigned to five treatment groups. All received intravenous calcium alone or combined with oral calcium pidolate or chloride boluses, liquid calcium or parenteral toldimfos. Plasma calcium, phosphorus, magnesium, parathyroid hormone, and calcitriol were measured before treatment and repeated up to 96 h post-infusion. Clinical outcomes, including time to standing, relapse, and alert downer status, were recorded. All cows stood following treatment. Nine relapsed and two of them were euthanized because of persistent recumbency. Adjunctive treatments did not improve clinical or biochemical recovery compared with intravenous calcium alone, which restored normocalcemia for approximately 8 h. Pretreatment calcitriol level was significantly lower in cows that relapsed than in those recovering within 96 h. Pre-treatment blood calcium was lower in cows with a single relapse but higher in alert downers. At 24 h, plasma calcium and phosphorus were lower in cows with a single relapse than in non-relapsing cows, whereas only plasma phosphorus was lower in cows with multiple relapses. These findings suggest that milk fever relapse may be linked to impaired calcium-vitamin D metabolism rather than phosphorus deficiency. Further research is warranted to confirm these results and optimize strategies for preventing relapses in dairy cows.