Comparison of the Hypercalcemic Action of Vitamins D2 and D3 in Chicks and the Effect on Tetracycline Fixation by Bone

Abstract

Doses of crystalline vitamins D2 and D3 ranging from 3 IU/day vitamin D2 and 40 IU/day vitamin D3 to 40,000 IU/day of each vitamin were administered daily to chicks fed a rachitogenic diet and the effects were noted on body weights, serum calcium and phosphorus, tetracycline uptake and bone microradiographic appearance. Although body weight and bone weight data indicated that vitamin D3 was approximately 10 times more toxic than vitamin D2 (about the same as the antirachitic potency difference), relative toxicity ratios could not be estimated from the effects on serum calcium level, or on bone ash. At all dose levels except at 40,000 IU/day, the vitamin D3 gave a higher percentage of bone ash than vitamin D2. No tetracycline was taken up by bones of chicks given 40,000 IU/day of vitamin D3 indicating no new bone deposition and a high degree of resorbing activity in these bones.