FORTIFIED CALCIUM BLOCK FOR HORSES ON PASTURE. Bighead, calcium deficiency and osteoporosis are significant problems for horses on sub-tropical grasses - including buffel, panic, kikuyu and setaria. Oxalates in these grasses bind calcium - making it unavailable to the horse and increasing the risk of a dietary calcium deficiency. Clinical signs of calcium deficiency, osteoporosis and nutritional secondary hyperparathyroidism include intermittent lameness, stiffness, shortened stride, tendon and ligament weakness, dental problems, weight loss and fractures. Lime and other inorganic forms of calcium supplements are also bound by oxalates only chelated calcium is safe from oxalates.