Calcium The calcium content in forages is affected by species, plant part (leaf versus stem), plant maturity, soil content of calcium and climate. Forages are usually a good source of calcium; cereal grains are not. Calcium in natural feedstuffs quite often exists as complexes with phytate and oxalate, which reduce the bioavailability. Further the bioavailability of calcium is affected greatly by the high calcium to phosphorus ratio in the diet. Many studies have shown that cereal grain based diets, alfalfa and various grasses and hays have low calcium availability. Additions of lactose and casein have been reported to increase the absorption and retention in both ruminants and non- ruminants. Supplements that are considered to have better calcium bioavailability values in order include calcium gluconate > monocalcium phosphate > dicalcium phosphate > anhydrous calcium chloride > bone meal > ground egg shell > > ground limestone > ground oyster shell > calcium sulphate > calcium carbonate.