Disodium EDTA is a chelating agent used in studies involving calcium. The sodium ion of the chelate is displaced by calcium to form soluble, non-toxic physiologically unavailable complexes that are excreted through urine. When EDTA binds the available calcium in the blood, an animal is forced into a state of negative calcium balance, a situation that mimics the principle of lowering dietary calcium in preventing milk fever. Although limited evidence is available, it is likely that calcium homeostatic mechanisms respond under such circumstances through the effect of parathyroid hormone and 1,25(OH)2 vit D3 on bone, gastrointestinal tract and the kidney. Investigations involving milk fever prevention by dietary manipulation using EDTA-induced hypocalcaemic or milk fever cow models should be interpreted with caution because EDTA is thought to be invasive to calcium homeostatic mechanisms.