Validation of an Enzyme Immunoassay for Measuring Fecal Cortisol Metabolites of Bearded (Sapajus libidinosus) and Black (Sapajus nigritus) Capuchins

Salivary cortisol captures endocrine response to an acute stressor in captive female tufted capuchin monkeys (Sapajus apella)

Measuring glucocorticoids such as cortisol is a useful tool for exploring relationships among behavior, physiology, and well-being in primates. As cortisol circulates in blood, it moves into biological matrices such as hair, urine, feces, and saliva. Saliva sampling is a simple, noninvasive method to measure cortisol that can be easily implemented by training animals to voluntarily provide samples. The temporal lag between elevation of cortisol in the blood and elevation of cortisol in saliva likely varies by species and must be characterized to identify appropriate sampling regimens. In the present study we characterized the time course of cortisol changes in saliva following an acute psychological stressor in captive tufted capuchin monkeys (Sapajus apella). We trained eight free-moving female tufted capuchin monkeys to voluntarily produce clean saliva samples. We exposed them to the acute stressor of a veterinary catch net and observed behavior pre and post exposure. We collected salivary samples immediately pre exposure (0 min) and 30, 45, 60, 75, 90, and 120 min after exposure. Salivary cortisol was quantified using a Salimetrics kit. Behavioral and cortisol measures were compared within individuals to a control condition in which no stressor was presented. Capuchins showed a clear behavioral response to the stressor by demonstrating increased freezing and pacing, decreased feed foraging, nonsocial play, and scratching, and decreased willingness to provide saliva samples after stressor presentation. After stressor presentation, average salivary cortisol began to increase at 30 min and continued to increase through the 120 min sample period. There was individual variation in absolute cortisol levels, the timing of the cortisol increase, and the timing of the peak. Our results suggest that no single time-point can be reliably used to evaluate salivary cortisol response to an acute stressor across individuals, and instead we recommend the collection of a prolonged time series.

Investigating the biological relevance of measuring gastrointestinal cortisol metabolite levels to assess stress responses in Atlantic salmon (Salmo salar L.) after an acute stress

Monitoring stress levels of farmed Atlantic salmon (Salmo salar) is important to ensure fish welfare and optimize farm operations. Feces could be a promising matrix for assessing stress responses in fish, based on their properties of low-invasive sampling and allowing repeated sampling over time. Meanwhile, elevated levels of cortisol metabolites (CMs) in feces indicate the increases in plasma cortisol levels (PLA) after exposure to acute stress. However, the dynamics of fecal CMs following acute stress in Atlantic salmon remain unclear. In this study, a confinement stress involving chasing and crowding was conducted to investigate the responses of gastrointestinal CMs to an acute stressor in Atlantic salmon. The post-smolts, with an average weight of 155.21 g, were sampled before and at 30 min, 1.5, 6, 12, 18, 24, 36, and 48 h after the onset of stress. Blood and gastrointestinal contents from the stomach, proximal intestine, and distal intestine of each fish were collected and subsequently analyzed, using competitive enzyme-linked immunosorbent assay (ELISA). The results demonstrated that the pre-stress level of PLA was low (4.28 ± 6.13 ng/ml) and reached a peak within 30 min following stress. The levels of CMs in gastrointestinal contents from stomach (SCMs), proximal intestine (PCMs), and distal intestine (DCMs) in pre-stress group were 0.82 ± 0.50, 18.31 ± 6.14 and 16.04 ± 6.69 ng/g, respectively. Gastrointestinal CMs increased significantly within 30 min and the peak levels of SCMs (3.51 ± 3.75 ng/g), PCMs (68.19 ± 23.71 ng/g) and DCMs (65.67 ± 23.37 ng/g) were found at 1.5 h post-stress. The significant increases in PCMs and DCMs post-stress validate the biological relevance of measuring intestinal CMs for assessing acute stress responses in Atlantic salmon. No significant difference was noted between PCMs and DCMs across all samples, suggesting that intestinal contents can serve as a suitable matrix compared with feces when measuring the responses of CMs to acute stress. The time lag between the peak of PLA levels and their reflection in the intestinal contents exceeded 1 h, indicating that using intestinal contents as a matrix to assess stress levels in fish can extend and delay the sampling window. This study highlights valuable guidance for determining the optimal times to utilize intestinal contents for measuring stress responses, providing further insights into the dynamics of fecal CM following acute stress.

Measurement of Salivary Cortisol in Two New World Primate Species

Glucocorticoids (GCs) are mammalian steroid hormones involved in a variety of physiological processes, including metabolism, the immune response, and cardiovascular functions. Due to their link to the physiological stress response, GC measurement is a valuable tool for conservation and welfare assessment in animal populations. GC levels can be measured from different matrices, such as urine and feces. Moreover, especially in captive settings, measuring GCs from saliva samples proved particularly useful as those samples can be collected non-invasively and easily from trained animals. Salivary GC levels can be measured using a variety of analytical methods, such as enzyme immunoassays. However, it is crucial to validate the analytical method for each specific application and species when using a new matrix. Using high-pressure liquid chromatography and a cortisol enzyme immunoassay, we show that the main glucocorticoids secreted in the saliva of squirrel monkeys and brown capuchin monkeys are cortisol and cortisone. Our biological validation found the expected salivary cortisol level to decline throughout the day. Our findings support the reliability of salivary cortisol measurements and their potential to be used as a valid tool in research and welfare assessment for these non-human primates.

Assessing stress in wild black-and-white colobus monkeys non-invasively

Analysis of glucocorticoid profiles serves as a valuable, multi-faceted tool for insight into the behavior and physiology of wild populations. Recently, the measurement of fecal glucocorticoid metabolites (FCMs) has exploded in popularity due to its compatibility with noninvasive techniques and remote environments A critical first step is to perform a biological validation to ensure that the assay accurately reflect changes in FCM levels. We use an enzyme immunoassay (EIA) to perform a biological validation on samples collected from two males and six females in a wild population of Colobus vellerosus in response to three naturally occurring potential stressors. We also describe the FCM response pattern in the week following parturition in three females and examine the influence of sex, reproductive state, and time of day on the concentrations of baseline samples collected daily from 13 adult individuals over a period of four months. We validated the assay: FCM levels increase in response to natural stressors with a two-day lag. In the two days surrounding parturition, FMC levels increased. Baseline concentrations were affected by collection time and female reproductive state, with lactating females having lower concentrations than pregnant or cycling females. Thus, we successfully carried out the first validation and characterization of FCMs in a wild African colobine. This will serve as an essential foundation for future studies of C. vellerosus and similar wild primates whose objective is to investigate the role glucocorticoids play in responses to social and ecological challenges.

Sex and dose-dependent responses of urinary and faecal glucocorticoid metabolite concentrations following an ACTH challenge in eastern rock sengis (Elephantulus myurus)

Non-invasive methods for measuring glucocorticoids and their metabolites are frequently used in ecological, behavioural and physiological studies of mammals. Using faeces, urine and other matrices for such a measurement has considerable advantages in comparison to more traditional methods, but also requires thorough validation of the methods used. Eastern rock sengis (Elephantulus myurus) are fascinating African mammals and the non-invasive monitoring of the adrenocortical activity opens up new opportunities to study their biology. We were able to validate two assays for measuring urinary (uGCM) and faecal glucocorticoid metabolite (fGCM) concentrations in this species using a dose-dependent challenge with adrenocorticotropic hormone (ACTH). A higher concentration of ACTH elicited higher uGCM and fGCM concentrations in both males and females. Interestingly, uGCM and fGCM concentrations and the responses to ACTH were higher in females than in males and small changes in faecal glucocorticoid metabolites could not be reliably detected in males. In contrast to ACTH, a saline injection did not result in an increase in uGCM or fGCM concentrations. The study also provided insight into when responses to a stressor are likely to be detected in the urine and faeces of sengis and opens up new opportunities to study the stress physiology of this and other sengi species. It further emphasises the importance of thoroughly validating non-invasive methods for measuring hormones in both sexes of a species and for incorporating dose-dependent approaches.

Non-invasive measurement of glucocorticoids: Advances and problems

Glucocorticoids (GCs; i.e. cortisol/corticosterone) are a central component of the stress response and thus their measurement is frequently used to evaluate the impact of stressful situations. Their metabolites from faeces of various animal species are more and more taken as a non-invasive aid to assess GC release and thus adrenocortical activity. The current literature review includes an extensive collection (1327 papers) and evaluation (see also Supplementary Tables) of the literature on faecal cortisol/corticosterone metabolite (FCM) analysis published to date. It aims at giving reference for researchers interested in implementing FCM analysis into their study or seeking to improve such methods by providing background knowledge on GC metabolism and excretion, conveying insights into methodological issues and stating caveats of FCM analysis and by highlighting prerequisites for and some examples of a successful application of such methods. Collecting faecal samples and analysing FCMs may appear simple and straightforward, but researchers have to select and apply methods correctly. They also need to be aware of the many pitfalls and potentially confounding factors and, last but not least, have to carefully interpret results. Applied properly, measurement of FCMs is a powerful non-invasive tool in a variety of research areas, such as (stress) biology, ethology, ecology, animal conservation and welfare, but also biomedicine.