Calcium and phosphorous build the mineral crystals which are responsible for the hardness and compressive strength of the skeleton. Calcium is also required for a normal function of muscle and nerve cells, and for the glands in the body.
Calcium deficiency in young horses will lead to abnormalities and metabolic diseases of the bones, including rickets and loose bone fragments in joints.
Good sources of calcium are mineral supplements (including calcium carbonate and dicalcium phosphate), alfalfa hay and most commercial feeds (look for mixes with 6-12 g/kg of calcium). Grass hays may
vary from 1.5 to 5 g/kg. It is recommended to insist on a feed analysis for calcium when buying large quantities of hay, especially when it is to be fed to young growing horses.