The biological assay of vitamin D3. The effect of the calcium and phosphorus content of the diet

Abstract

The effects of varying Ca and P contents of standard diet on the gain in wt., tarso-metatarsal distance and % of bone ash of tibia of chicks were related to graded doses of vit. D. The maximal spread of avg. responses, the steepest slope of the response line and the maximal reliability of assays were obtained with 1.5% Ca and 1.5% P in the diet. Variations of [plus or minus]20% in these amts. produced no significant change in the slope and reliability. The regression of response on log dose is linear between 10 and 22.5 B.S.I. units of vit. D3/100 g. of food. The bone ash criterion of response gave greater reliability, but the gain in wt. and tarso-metatarsal distance are simpler and more economical to use. A marked fall in serum phosphatase was observed with increase in vit. D3 intake.