Bone can be formed via two pathways: by straight bone formation or by a cartilage template that develops into bone. There are three types of bone cells: osteoblasts (make bone), osteoclasts (remove bone) and osteocysts (osteoblasts trapped in the matrix of bone that are weight bearing sensors). Bone is deposited at sites where it is required and resorbed where it is not. A calcium deficiency will lead to swollen facial bones (fibrous osteodystrophy) in horses and goats, but sheep and cattle get osteoporosis (reduced quantity of normal quality bone). Vitamin D deficiency or phosphorus deficiency will lead to rickets (in young animals ) and osteomalacia (in older animals). Carotenes are antagonists for vitamin D.
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