Some assay restrictions on inferences made from determining hormones in horses, cows, and their fetuses

Often in developing hormone assays, hormones that may interfere with the assay by cross‐reaction are not available for testing the validity of the assay. For example, horse TSH was unavailable to test for cross‐reaction in an LH radloimmunoassay (RIA). The authors devised an indirect means of accomplishing the same goal, and the evidence from the indirect test of cross‐reaction was at least as persuasive as a direct test might have been. Other examples are given of experiments where extensive effort was devoted to validation of steroid RIA, but there were substantial quantitative differences in the results among experiments and among laboratories. Differences of this kind probably would be intolerable in an assay used to monitor hormone residues in food‐producing animals.