Studies on Milk Fever in Dairy Cows. V. The Effect of Massive Oral Doses of Vitamin D on Absorption, Excretion, Retention and Blood Levels of Calcium and Phosphorus

The efficiency of calcium absorption and mobilization is involved as a major contributory factor in the onset of milk fever.A study concerned with changes in the physiological behavior of calcium and phosphorus when massive doses of vitamin D are fed to dairy cattle assumes significant importance.Recent development of radioisotope procedures for the separate estimation of endogenous and exogenous fecal calcium and phosphorus provided the means for further study of this important problem. Editor.This study is concerned with changes in the physiological behavior of calcium and phosphorus when massive oral doses of vitamin D are fed to cattle.Recently Hibbs and Pounden (13) have shown that 30 million units per day of vitamin D fed 3-8 days prepartum prevented milk fever in mature cows with previous milk fever histories.The protection afforded by vitamin D was attributed to its calcemic effect, which was indicated by the relatively high blood calcium level maintained during the critical postpartum period.Other studies (24) have suggested that the increased blood calcium level was not due to parathyroid stimulation, because parathyroid activity was suppressed after 7 days of vitamin D feeding at thirty million units per day.In support of this, various workers (1, 15) using other species have found that calcemic doses of vitamin D increased absorption of calcium from the intestine, but parathyroid hormone secretion actually declined (1) and parathyroid size decreased (16).The fact has been established experimentally in a number of species that vitamin D increases the absorption of calcium and phosphorus when added to a diet low in vitamin D (6, 10, 17, 19).These findings suggest that the calcemic effect of vitamin D is elicited chiefly through an increased intestinal absorption of calcium and phosphorus.