Bioassay of vitamin A in liquid supplements.

Vitamin A bioassay techniques based on liver storage in the chick were adapted for the assay of vitamin A in molasses based liquid supplements for cattle. Methods of administering the assayed supplement to the chicks were: 1) direct dosing of the supplement via four crop infusions at hourly intervals and 2) ether extraction, suspension in cottonseed oil with solvent removal in vacuo followed by direct crop dosing. The last method allowed a larger dosage with fewer analytical problems. Five sequential extractions were required for 97% recovery of the vitamin A from the molasses supplement. With the higher dosage range, the variance of response was a function of dose level. Transformation to a log dose - log response curve allowed a linear plot with homogeneity of variance. Detection of a 10% loss of vitamin A potency (P less than .10) was estimated to require 27 chicks per treatment by the slope ratio bioassay procedure.