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Occurrence in Blood Plasma from Certain Dairy Calves of Factors that Interfere with the Color Reactions of Activated Glycerol Dichlorohydrin with Vitamin A and Carotenoids¹

Iowa State College, Ames

ABSTRACT

Samples of blood plasma from calves were analyzed for vitamin A and carotenoids by saponification and by nonsaponifieation methods using activated gly-cerol dichlorohydrin (GDH) as the colorimetric reagent.

The accuracy of analysis, as measured by the use of internal standards, was increased by saponification of plasma.

Low vitamin A values occasionally found by the nonsaponifieation method are attributed primarily to the presence of inhibitors of color reactions.

Color suppressing factors apparently contributed to the low carotenoid levels found in some nonsaponified samples of calf blood plasma.

Although a marked variability among individual calves was noted, there appears to be a possible relationship between diet and the presence of color inhibitors in blood plasma.

Since there is no known method of predicting the presence of substances that suppress the color reactions, it is recommended that all calf blood plasma samples be analyzed by the saponification method when GDH is used as the colorimetric reagent.

¹ Journal paper no. 1630 of the Iowa Agricultural Experiment Station. Project no. 814.