Available animal models of osteopenia--small and large.

Animal models of osteopenia are reviewed. Endocrine excess or deficiency conditions include ovariectomy, orchidectomy, glucocorticoid excess and other endocrine states. Seasonal and reproductive cycles are usually transient and include pregnancy and lactation, egg-laying, antler formation and hibernation. Dietary conditions include calcium deficiencies, phosphate excess and vitamin C and D deficiencies. Mechanical usage effects include skeletal underloading models. Aging is also associated with osteopenia in many species.