Saliva and Blood Cortisol Measurement in Bottlenose Dolphins (Tursiops truncatus): Methodology, Application, and Limitations

Abstract

A central task of zoos and aquaria is the frequent and accurate assessment of their animals’ welfare. Recently, important steps have been made, such as the introduction of animal welfare evaluation tools and welfare decision trees. To determine animal welfare, it is not only important to collect life history data, such as longevity and reproductive success, but also for experienced observers or caretakers to conduct behavioral observations on a regular basis to assess animals’ emotional state. To physiologically validate welfare observations, glucocorticoid levels are usually assessed, as they are a common indicator of stress. While, for many animals, these levels can be easily determined via fecal or hair samples, for cetaceans, the levels are usually determined via blood samples. As blood samples cannot be taken very frequently and the process may cause stress to the animals (if the samples are not taken following medical training), other techniques, such as the measurement of health biomarkers (especially cortisol, which can be measured in saliva), have become the focus of cetacean stress research. However, there are two problems associated with saliva measurements in cetaceans: saliva might either be diluted with pool water or be contaminated by fodder fish, as frozen fish usually contains high levels of cortisol. In our study, we investigated how saliva cortisol levels are connected to blood cortisol levels and how saliva cortisol can be influenced by fodder fish. We examined saliva and blood samples in eleven bottlenose dolphins (Tursiops truncatus) kept in an outdoor and indoor facility in Germany. Furthermore, we assessed the cortisol levels of different kinds of fodder fish. Our data show that, although saliva cortisol values are elevated under stress and arousal, they seem not to be correlated with blood cortisol values. We also show that, after feeding, saliva cortisol values are increased up to 100-fold. Our results suggest that saliva cortisol measurements in dolphins have to be conducted and considered with care, as they can easily be contaminated. Moreover, it is important to use the right laboratory method in order to specifically detect cortisol; in our study, we conducted reliable tests, using LC-MS/MS.

Use of modern geometric design of fish ponds to increase welfare and blood parameters

“…Stress can depress the immune system, which increases the amount of circulating heterophils 41 . Therefore, MGD contributed to providing fish with more welfare due to its comfortable movement and free swimming in the water, which helped reduce their stress hormones and decreased the H/L ratio 15 . The MGD contributed to improving welfare and promoting a healthy H/L ratio, for example, by providing fish with a clean, comfortable environment and feeding animals a healthy diet.…”

“…One study published in the journal Animals in 2022 found that fish raised in rectangular ponds with rounded corners had lower blood cortisol levels than fish raised in square ponds. Cortisol is a stress hormone, so this suggests that the rectangular ponds with rounded corners were less stressful for the fish 15 . The fish raised in circular ponds had higher levels of some blood proteins, including albumin and immunoglobulin G, than fish raised in rectangular ponds.…”

Towards understanding host–pathogen dynamics of cetacean poxvirus: attainable approach through the application of a repetitive non-invasive skin sampling in bottlenose dolphins (Tursiops truncatus) under human care

“…Thus, the goal of any investigation developed in those facilities might be conducted along with the enhancement of innovative approaches and/or the improvement of sampling techniques to assess their well-being through minimally-or noninvasive methods, usually aiming to avoid long-lasting manipulations of animals (Zemanova, 2020;Schilling et al, 2022). Hence, different methods that minimize impact while sampling marine mammals in managed care have been reported, including the use of exhaled breath condensate to examine respiratory-associated microbial microorganisms (Lima et al, 2012), rubberized scrapers to obtain sloughed skin to further determine skin cortisol concentrations (Bechshoft et al, 2015), or swabs to collect saliva (Rickert et al, 2022), among others.…”

Stimulated Parotid Saliva Is a Better Method for Depression Prediction

“…For most biotypes, cortisol levels are at their highest in the morning, which can reflect the function of the adrenal cortex, usually around 9 a.m. [ 15 ]. Saliva has been proven to have high correlation values to cortisol levels in blood with a non-invasive in situ collection method, so it is more lucrative for cortisol determination compared with blood [ 16 , 17 ]. In clinical practice, about 80% of the cortisol in the blood is combined with cortieosteroid-binding globulin (CBG), and the rest is in a free state [ 18 ].…”