Absorption and Tissue Distribution of Radiocalcium in Cattle1

Abstract

Radiocalcium studies with 21 Hereford cattle in the age range of seven to 36 months have provided considerable basic data which are presented and from which the following conclusions were drawn: The fecal excretion of calcium as determined by chemical analysis was 85±17 percent of the dietary intake; the fecal excretion of orally administered radiocalcium was 66±8 percent. About 15 percent of intravenously administered radiocalcium was excreted in the feces and 0.3 percent in the urine which means that about 85 percent of the dose reached the skeleton. Circulating calcium was secreted into all parts of the gastroin-testinal tract with the small intestines playing a major role. Circulating calcium atoms are continuously and rapidly being removed from the blood and are replaced by calcium atoms absorbed from the tract and those exchanged out of the skeleton. Calcium ions in the soft tissues are generally interchangeable with those in the plasma. In general, the accumulation and turnover of calcium in the various bones parallel the metabolic activity.