Towards a digestible calcium system for broiler chicken nutrition: A review and recommendations for the future

There is growing awareness that variability in the nutritional quality of Ca sources has significant effects on gastrointestinal pH, P and amino acid digestibility, exogenous enzyme efficacy and the microbial population in the gastrointestinal tract of broilers. In this regard, the interest in moving toward a digestible Ca system is gaining traction and the apparent ileal digestibility (AID) or standardized ileal digestibility (SID) coefficients for Ca in ingredients, such as limestone (n = 55), dicalcium phosphate (DCP; n = 21), meat and bone meal (MBM; n = 20), monocalcium phosphate (MCP; n = 12), and plant-based ingredients are available. The aim of this review was to compile the literature evaluating Ca digestibility of feed ingredients for broilers, highlight factors that may influence the digestibility coefficients, and suggest recommendations to move toward a digestible Ca system. There were 11 papers published between 1974 and 2019 focused on the evaluation of Ca digestibility of feed ingredients for broilers. The average ileal Ca digestibility coefficient for limestone was 0.53, DCP was 0.42, MCP was 0.35 and MBM was 0.46. There were no differences in the AID or SID Ca digestibility coefficients within ingredient. The ileal Ca digestibility coefficient for limestone increased (quadratic, P 1:1 or to 16 h for diets with a Ca:NPP ratio