Some Biokinetic Aspects of Calcium Metabolism in Dairy Cows

Abstract

A study was made to determine how cows which have been prefed low Ca:high P diets are better able to maintain normal serum Ca levels than are cows prefed high Ca:low P diets. Radioactive calcium (Ca⁴⁵) was employed as a tracer. A procedure is presented by which the reservoirs of mobilizable skeletal Ca may be estimated. It appears that these reservoirs of skeletal Ca are larger and are turning over more slowly in cows which were prefed low Ca:high P diets. Since we found earlier that the low Ca: high P cows were in negative calcium balance, the larger stores of mobilizable Ca must accrue at the expense of stable bone Ca. A comparison of bone Ca specific activity to serum Ca specific activity indicates that nearly all the trabecular bone Ca and from 7 to 17% of the cortical bone Ca (depending upon dietary Ca/P) may be included in the ‘mobilizable Ca pool.’