Effect of calcium and fat intake on calcium metabolism in calves.

Ten male Holstein calves were fed diets with or without 5% added animal fat in combination with low and high dietary calcium (.15 or .98%) for 4 wk. After 3 wk, the animals were orally dosed with calcium-45. One week later they were killed and tissue samples taken. Except for lower calcium-45 in bile, added dietary fat had no marked influence on calcium metabolism. Net absorption of calcium-45 (not excreted in feces) ranged from 82% for calves fed low calcium to 53% for those given high calcium. Calcium-45 in bone was substantially higher in calves fed .15% calcium. Tailbone biopsies revealed rapid uptake of calcium-45 with approximately as much incorporated during the 1st d as in the following 6 d. Calcium-45 in blood peaked 24 h following dosing. Calves fed .15% calcium had higher calcium-45 in blood and bile than those receiving .98% calcium. Calcium-45 values in soft tissue were low and did not differ materially among treatments. The decreases in radioactive calcium absorption and bone deposition with higher dietary calcium indicated that variable absorption was a major factor in calcium homeostasis. Added fat did not materially effect calcium metabolism with either low or high dietary calcium.