Calcium constitutes more than a third of the total mineral content of an adult bird.

The most prevalent mineral in the body is calcium; it is required in the diet in greater amounts than any other mineral.

In the egg laying female, most dietary calcium is used for shell formation.

Many foods are deficient in calcium, and requirements are highly variable so supplying adequate calcium is very challenging.

Calcium absorption is tightly controlled and several mechanisms exist in the body to regulate calcium uptake.

Factors interacting to control calcium absorption include – parathyroid hormone, Vitamin D, calcium binding protein, dietary calcium level, form of the calcium in the diet, amount of fat in the diet, size of the calcium particles, acidity in the gut and strength of the gizzard! No wonder it is difficult!

Calcium in plants (often the calcium is bound to oxalate or phytate) is poorly digested. So even though the analysis may show a reasonable calcium level it may not be absorbed. Furthermore, the phytate in the plant may reduce the calcium absorbed from other sources.

During egg shell formation calcium carbonate is produced and goes to create the egg shell. The amount of calcium in the blood of the bird is enough for about 15 minutes of shell formation – for the remaining time (15 – 20 hours) calcium needs to be absorbed from the gut or released form the bones.

Small birds lay proportionally larger eggs than large birds, and small eggs have proportionally more shell. Thus the calcium requirement of small birds is greater than that of larger birds.

Zebra finches will exhaust all the calcium in their skeleton after 5 eggs – they need to have a constant calcium intake during the laying period!