Consideration of mineral homeostasis when conducting calcium nutrition work in poultry

Optimal dietary calcium levels are necessary for efficient growth, bone mineralization, and eggshell calcification in poultry. To properly assess nutritional requirements at all physiological stages, a holistic understanding of mechanisms governing both calcium and phosphorus homeostasis is necessary. Intestinal uptake, renal reabsorption and excretion, and bone remodeling of both minerals involve the integrated action of bioactive 1,25-dihydroxycholecalciferol, parathyroid hormone, calcitonin, and fibroblast growth factor 23 on the intestine, kidney, and bone. In laying hens, eggshell calcification imposes additional demands on these systems. Hormonal regulation of intestinal and renal calcium and phosphorus transporter expression and activity is highly dependent on vitamin D₃ status, in addition to both absolute and relative dietary levels of calcium and phosphorus. This symposium paper will provide an overview of the regulatory systems governing calcium homeostasis, with a particular focus on hormonal regulation, intestinal uptake, and aspects of laying hen physiology that must be considered when designing calcium nutrition studies and interpreting findings in a meaningful way.