Radioimmunoassay technique for measuring cortisol in milk.

A sensitive radioimmunoassay procedure for measurement of cortisol has been developed for use in whole or skim milk. Cortisol concentrations were similar in whole and skim milk indicating that this steroid is not associated with milk lipids. Because of this relationship, the use of skim milk provides a faster and much simplified approach to the study of cortisol in milk. Mean and standard errors of cortisol concentrations in skim milk samples collected at 2400 and 1200 h from seven cows for 1 wk were .71 +/- .05 and .69 +/- .07 ng/ml. Cortisol in colostrum averaged 1.59 +/- .07 ng/ml.