Calcium

What it does

Calcium is a macromineral, and the requirements for calcium and phosphorus are much higher during growth, late pregnancy and lactation than at maintenance ^[1].

Deficiency

Uncomplicated deficiencies are rare in horses; problems usually come from imbalances. Horses on grass hay or pasture that are also fed large amounts of unfortified grain-based concentrate or wheat bran are the most likely to develop a calcium deficiency ^[1].

A reversed Ca:P ratio or excess phosphorus can inhibit calcium absorption, causing skeletal abnormalities and nutritional secondary hyperparathyroidism ^[1].

Excess

Rations above 1% calcium should be avoided in horses with reduced kidney function or a history of urinary stones ^[1]. Excess calcium makes vitamin D toxicity worse ^[1].

The Ca:P ratio

Keep the Ca:P ratio above 1:1; about 1.5:1 is desirable, and foals may tolerate up to 3:1 if phosphorus is adequate ^[1]. A&L Canada gives about 2:1 as desirable ^[2].

Testing

Blood concentrations of macrominerals, especially calcium, don't adequately reflect intake ^[1]. Mineral values on feed reports are given in percent for the macrominerals ^[2].

See also phosphorus, vitamin d3, mineral ratios.