Reunderstanding the Mechanism of Bone Resorption in the Regulation of Postpartum Hypocalcemia in Dairy Cows: Insights from Cross-Species Evidence

Some dairy cows develop postpartum hypocalcemia because they cannot adapt to the drastic loss of blood calcium during the periparturient period. Parathyroid hormone (PTH) maintains calcium homeostasis by regulating bone calcium mobilization, gastric and intestinal calcium absorption, and renal calcium reabsorption. Traditionally, dysregulation of PTH has been considered the main cause of this disorder. Recent studies have confirmed that parathyroid hormone-related protein (PTHrP) secreted by the mammary gland is also involved in calcium homeostasis by promoting bone resorption. Based on existing research evidence and cross-species comparisons, this paper analyzes the effects of differences in mammary calcium output and compensatory mechanisms among various mammals on the risk of postpartum hypocalcemia, with a particular focus on processes related to bone resorption and bone formation. It further explains the pathogenesis of postpartum hypocalcemia in dairy cows by examining the roles of the mammary–brain–bone axis, PTH, and PTHrP in bone resorption and bone formation in these animals.