Reducing Dietary Calcium and Phosphorus Concomitantly During a Depletion–repletion Cycle Improves Phosphorus Utilization: A Meta-analysis Approach

Abstract Calcium (Ca) and phosphorus (P) extracellular concentrations are tightly maintained by complexe regulation system. It is thus possible to perform nutritional or physiological conditioning of an animal to enhance its efficiency of phosphorus (P) use and reduce the amount intake and excreted. Consequently, nutritional strategies that take advantage of the animal’s metabolic adaptability—such as depletion–repletion protocols—have been developed. A database was compiled including studies investigating Ca and P depletion-repletion in growing pigs. Diets were kept constant between control and depleted animals except for differences in Ca and P levels. This approach allowed data to be expressed relative to the control pigs (in %) for both Y and X variables. The database contained 16 depletion–repletion sequences from 8 publications. The effect of the study was included in the statistical model as a random effect, the Y variable was bone mineral content (BMC, %control) and X variable was Ca and P reduction intensity (% vs control) during depletion and repletion which were included as a fixed effect and their interaction were tested. During depletion, the BMC (Table 1) was most reduced (approximately 85% of control) when both Ca (P = 0.002) and P (P = 0.071) were reduced. This is consistent with the fact that both Ca and P are required, and in a particular ratio related to their deposition as hydroxyapatite, to ensure bone mineralization. A single decrease in Ca does not decrease mineralization as much, perhaps related to Ca homeostasis. Regarding repletion, an increased retention efficiency was observed in animal depleted in P (linear, P = 0.008; quadratic, P = 0.018) and Ca simultaneously but not for those depleted only in Ca (linear, P = 0.004). This could be due to calcium regulation involving parathyroid hormone, one of whose actions is to increase phosphaturia, which could limit catch-up capacity. Overall, Ca appears to be the main driver of phosphocalcic metabolism in growing pigs. An in vivo trial is currently being conducted to validate these hypotheses.