A Quantitative Method for the Assay of Vitamin D with Chickens

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Abstract
A quantitative method is described for the assay of vitamin D with chickens. It is based on the determination of femur ash, and the interpretation of the ash percentage by means of either of two response curves, one for cod liver oil and the other for irradiated ergosterol. The method has been analyzed in regard to probable error, and means provided for the easy estimation of error, with any given number of chickens, in both direct assays and in assays of one substance in terms of another. Under the most favorable conditions the probable error of an assay of irradiated ergosterol with ten chickens is as little as 9% of the unitage found. A slightly smaller error is experienced in assays of cod liver oil. With the diet used, which had Ca:P = 2:1 (optimal for young chicks), good calcification resulted from the addition of 18 I.U. of vitamin D, as cod liver oil, per 100 gm. of ration. Explanation of conflicting reports on the relative effectiveness, rat unit for rat unit, of cod liver oil and irradiated ergosterol for chickens, was found in the fact that these sources are not broadly comparable. Their relative efficacy fluctuates with the degree of calcification, the difference being small at low calcifications, 100 times at ‘normal’ calcification, and very great in the production of extra-hard bone.