Radioimmunoassay for Cortisol in Pig Saliva and Serum

An “in-house” radioimmunoassay (RIA) procedure utilizing commercial sources of antiserum and radiolabel was developed for the simultaneous measurement of cortisol in serum and saliva from swine. A commercial RIA kit (Incstar) for cortisol was used to validate the in-house procedure for serum measurements. The correlation coefficient (r) between the Incstar kit and the in-house method for serum cortisol was 0.94. The Incstar kit was modified to accommodate measurement of salivary cortisol concentrations and compared to the in-house procedure. The correlation between these procedures was r = 0.81 and best described by a logarithmic (Ln) curve. Salivary cortisol measures by the in-house RIA were significantly higher than those obtained from the modified Incstar kit (p < 0.01), a probable consequence of the different relative cross-reactions of the respective antisera to cortisone and a dilution effect on the kit standards. Keywords: Radioimmunoassay; salivary cortisol; pigs; stress