Salivary vs. serum cortisol for the assessment of adrenal activity in swine

Abstract

The efficacy of salivary cortisol analyses for assessment of the hypothalamic-pituitary-adrenal (HPA) response to stimulation is compared to serum cortisol measurement. Matched samples of serum and saliva were collected from pigs (n = 6) subjected to exogenous adrenocorticotrophic: hormone (ACTH) stimulation (i.v. 200 IU) and snaring. Salivary cortisol responses to handling and transport (1 h) were measured in a further 10 pigs. Saliva samples were collected before and after handling and transport. There were significant correlations between serum and salivary cortisol values, following ACTH stimulation (r = 0.8813, P < 0.025), and snaring (r = 0.7964, P < 0.05). The overall ratio of saliva to serum cortisol was 9%. The saliva:serum cortisol ratio was concentration dependent. In pre-stimulation samples the ratio was 8.6% and at maximal concentrations was 13.3%. Handling and transport stress stimulated increases in salivary cortisol concentrations. Differences between pre- and post-transport concentrations were significant (P < 0.0001). Variation in the concentration of cortisol-binding globulin (CBG) is an important factor for the interpretation of adrenal response. Salivary "free" cortisol may be a better indicator of stress than "total" cortisol measured in blood samples.