Salivary Cortisol as a Measure of Acute Stress and Diurnal Adrenal Activity in Bottlenose Dolphins

ABSTRACT Monitoring changes to animals' physiological states in managed settings is critical in modern animal welfare assessment. Under human care, marine mammals can be conditioned for voluntary biological sample collection, reducing effects of handling stress on physiological state, thus better reflecting normal physiology. This study validated the use of salivary cortisol in bottlenose dolphins as an alternative to blood cortisol for evaluating acute adrenal response to a controlled physiological stressor. Time‐matched blood and saliva were collected from nine bottlenose dolphins before, during, and after out‐of‐water annual vaccination, and analyzed by enzyme‐immunoassay. Significant short‐term peaks in cortisol occurred similarly in both blood and saliva occurred during vaccination, validating detection of a marked adrenal response. We also measured diurnal variation in salivary cortisol over daylight periods in 12 dolphins over 15 days. Salivary cortisol exhibited a detectable diurnal rhythm in males only, with peaks occurring at first sampling and declining throughout the day. Both intra‐ and interindividual differences in mean salivary cortisol levels were detected, highlighting the need to establish normal baseline parameters at an individual level for welfare assessment. This sampling approach demonstrated the potential for voluntary serial saliva sampling in animal care facilities as a welfare monitoring tool.