Cholecalciferol requirements of young turkeys under normal conditions and during recovery from rickets.

Day-old turkeys fed vitamin D-deficient diets became rachitic within 17-24 days. The symptoms included reductions in body weight, plasma calcium and inorganic phosphorus, plasma and intestinal calcium-binding protein (CaBP), plasma 25-hydroxycholecalciferol [25(OH)D3], bone ash, and kidney 25(OH)D3-24-hydroxylase and a rise in kidney 25(OH)D3-1-hydroxylase activity. Supplementation of the diet with 12.5 micrograms cholecalciferol per kilogram was sufficient to promote maximal body weight and normal plasma calcium, Plasma calcium, plasma phosphorus and bone ash. Feeding diets containing 250 or 1250 micrograms cholecalciferol per kilogram resulted in a reduced body weight. An increased in the concentration of plasma 25(OH)D3 with increasing dietary cholecalciferol concentration was observed. Feeding vitamin D-deficient rachitic birds for 4 days a diet containing 50 micrograms cholecalciferol per kilogram restored plasma calcium and phosphorus and bone ash. Body weight remained lower than that of the control for an additional 6-day period. Additional cholecalciferol, 25(OH)D3 or 1 alpha-hydroxycholecalciferol in the diet, intramuscular injection of the vitamin D derivatives, or a high-calcium, high-phosphorus diet did not accelerate the recovery from the rachitic state.