The Antirachitic Activity of Various Forms of Vitamin D in the Chick

Abstract

Crystalline vitamin D₃ assayed by the U.S.P. antirachitic vitamin D test on rats has a potency of 0.025 γ per unit or 40,000,000 units per gram. This is identical with the potency of crystalline vitamin D₂. The minimal protective daily dose for chicks fed a rachitogenic diet was found to be 2.5 I.U. of cod liver oil, 2.5 I.U. of crystalline vitamin D₃, 2.7 I.U. of irradiated cholesterol, 120 I.U. of Viosterol (A.R.P.I. process) and 85 I.U. of crystalline vitamin D₂. The antirachitic ratio of effectiveness of cod liver oil to Viosterol (A.R.P.I. process) rat unit for rat unit in the chick is 1:48. The ratio for vitamin D₃ to vitamin D₂ is 1:34. The reasons for the variations in potency of vitamin D preparations when tested on rats and chicks are discussed.