Implementation of a digestible calcium system: Why is it needed and where are we?

The regulation of blood calcium (Ca) and phosphorus (P) levels are closely intertwined, requiring that their metabolically available supply in the diet be carefully balanced. The majority of the P in plant-based feed ingredients is stored as phytate, which is poorly digestible by broilers, while inorganic P sources also show significant variability in digestibility. For decades, poultry nutritionists have incorporated available P in diet formulation, recognizing that the digestibility of P in feedstuffs is highly variable. In contrast, poultry diets are still formulated on a total Ca (tCa) basis, overlooking the variable digestibility of Ca from different dietary sources. Incorrect assumptions regarding the digestibility of Ca can lead to Ca imbalances, which negatively affect both broiler health and overall performance. Furthermore, the influence of Ca and limestone on phytase efficacy, which plays a critical role in enhancing P availability by breaking down phytate, is highlighted. As the poultry industry moves towards implementing a digestible Ca (dCa) system, the development of accurate prediction equations for limestone digestibility becomes essential. Such an approach not only improves the precision of diet formulation but also enhances overall broiler performance by ensuring a more balanced and metabolically available supply of both Ca and P. Transitioning to a dCa system, in conjunction with phytase use, represents a critical step in optimizing nutrient efficiency and improving sustainability in modern poultry production.