Calcium and Magnesium Utilization in Rats: Effect of Dietary Butterfat and Calcium and of Age

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Abstract
This factorial study was designed to examine the effect of short- and long-term ingestion of dietary calcium (0.25% and 1.0%) and butterfat (5% and 20%) and treatment with dimethylhydrazine (DMH) in rats. Calcium, magnesium and phosphorus absorption and, to a lesser extent, total diet digestibility decreased as the rats aged from 2 to 8 mo. Increased ingestion of butterfat had no effect on apparent absorption of calcium among young rats but tended to decrease calcium absorption in mature rats. The weak effect (P < 0.05) of butterfat on calcium absorption reflected the small amount of calcium (< 2% of fecal calcium) associated with lipids in feces. Ingestion of 10 vs. 2.5 mg Ca/g diet reduced the efficiency of apparent absorption of calcium, magnesium and phosphorus of young and mature rats and resulted in slightly, but significantly, greater retention of calcium in bone after 27 wk. The total amounts of calcium retained in tibias were correlated with the amounts of calcium absorbed by rats after 4, but not after 27, wk of dietary treatments. Rats dosed with DMH exhibited improved efficiency of calcium absorption, but the incidence of intestinal tumors did not affect mineral utilization.