[Comparative antirachitic activity of vitamins D2 and D3 in the body of chicks].

In the four-week study the antirachitic action of vitamin D2 in different does (5000, 7500, 10 000 I. U. per kg food) and of vitamin D3 in a dose of 500 I. U. per kg food was investigated in chicks. The vitamin efficiency was measured with respect to the following seven parameters: weight gain, serum content of Ca and P, serum activity of alkaline phosphatase, bone ash content, content of Ca-binding protein in the duodenal mucosa, and weight of parathyroid glands. In regard to these parameters, vitamin D2 in a dose of 7500 I. U./kg and vitamin D3 in a dose of 500 I.U./kg produced a similar effect. Thus, the antirachitic effect of vitamin D3 was 15 times higher than that of vitamin D2. In the three-day study of the effect of vitamins D2 and D3 on the synthesis of Ca-binding protein it was found that they exerted a similar effect when the dose of vitamin D2 was 14.5 times higher than that of vitamin D3.