Recent studies of bone appetite in cattle

Cows depleted of phosphorus by loss of saliva from a parotid fistula and low dietary phosphate developed an avid appetite for bones. The behaviour is innate and predominantly cued by olfactory stimuli. Meat, blood or fat were not attractive and bones became more attractive after aging for 1.5-2.0 years. The appetite was also shown for guano-derived rock phosphate and bird excreta. There was no interest in inorganic calcium and phosphate salts or ashed bone. The attractant is therefore an organic constituent of aging bone and was found to be at highest concentration in the marrow fraction. Water, ether and vacuum distillation extracts of old bone or marrow, added to unattractive materials e.g., ashed bone, rendered them attractive. The residues of such extraction were of diminished interest. The attractiveness of the fractionated extracts was highest in the neutral fraction. The bone appetite was abolished by increasing the phosphate concentration in plasma but not in cerebrospinal fluid. The phosphate concentration in the blood appears, therefore, to regulate the bone appetite. The sensors could be in brain regions without a blood-brain barrier. Chronic severe phosphorus deficiency was associated with bone resorption, reduced osteoblastic and hemopoietic activities, and abnormal blood progesterone cycles.