Calcium Regulation in Birds

Calcium plays two important physiological roles in the avian subject. First, it provides the structural strength of the avian skeleton by the formation of calcium salts. Second, it plays vital roles in many of the biochemical reactions within the body via its concentration in the extracellular fluid. The control of calcium metabolism in birds has developed into a highly efficient homeostatic system, able to quickly respond to increased demands for calcium required for both their ability to produce megalecithal eggs and their rapid growth rate when young. Parathyroid hormone (PTH), metabolites of vitamin D3 and calcitonin, regulate calcium as in mammals, acting on the main target organs of liver, kidney, gastrointestinal tract and bone. Estrogen and prostaglandins also appear to have an important role in calcium regulation in the bird.