Final answer:
Calcium makes up 70% of the horse's bone structure. It is a constituent of bones and teeth and plays a crucial role in biological processes.
Step-by-step explanation:
Calcium makes up 70% of the horse's bone structure. It is a constituent of bones and teeth, primarily in the form of crystals of hydroxyapatite, along with phosphate. In the complex salts of bone, 70% of the total magnesium content of the body is combined with calcium and phosphorus. Calcium also plays a crucial role in various biological processes.