Fecal cortisol radioimmunoassay to monitor adrenal gland activity in the bottlenose dolphin (Tursiops truncatus) under human care

Fecal glucocorticoid measurement is an important noninvasive tool to monitor animal health. A radioimmunoassay (RIA) method was developed to measure fecal cortisol in bottlenose dolphins under human care. The method was used to measure baseline hormone levels and evaluate the adrenal response to environmental challenges in a small number of individual dolphins. The method was validated by precision and accuracy tests and by comparison with liquid chromatography-mass spectrometry (LC-MS). The parallelism test suggested few matrix interferences. The assay showed a good degree of precision within assay (CV = 5.4%) and between assays (CV = 4.1%). The RIA significantly correlated with the LC-MS method (r = 0.838, P < 0.01). The recovery test and the comparison between RIA and LC-MS suggested that the RIA slightly underestimates fecal cortisol concentrations, although the degree of accuracy was good. This study established that bottlenose dolphins excrete appreciable amounts of fecal cortisol (healthy subjects: 0.2-9.5 ng/g). Therefore, chronic HPA axis activation may be monitored in fecal samples by immunoassays after validating a suitable extraction protocol. The RIA could discriminate conditions of stimulation (pregnancy, parturition, isolation, transportation) and inhibition (diazepam administration) of the HPA axis and may, therefore, be useful for monitoring dolphin well-being.