Glucocorticosteroid concentrations in feces and hair of captive caribou and reindeer following adrenocorticotropic hormone challenge

The influence of selected factors on wool cortisol concentration in alpacas (Vicugna pacos)

Several internal and external factors can influence animals' hormonal activity. Cortisol level in hair and wool determines chronic stress, which is connected with the long-term HPA axis effect. Wool cortisol levels in alpacas have never been determined to this time. The study aimed to assess the influence of selected factors on wool cortisol concentration in alpacas. The study included 36 alpacas. Wool samples were collected during shearing in June 2021, cut with an electric clipper from the right shoulder and the rump. Wool samples were fragmented into proximal (winter-spring regrowth) and distal (summer-fall regrowth) segments. Alpacas' Heat Stress Index (HSI) for the summer of 2020 was 139.4, and 116 for the winter of 2021. The cortisol levels in the wool samples were determined with the General Cortisol ELISA Kit assay. The most significant differences in wool cortisol concentrations were caused by two factors: the wool segment (P < 0.001; η2 = 0.889) and the region on the body (P < 0.001; η2 = 0.876). Wool cortisol level was higher in the distal segment (referring to the summer-fall season) than in the proximal one (referring to the winter-spring season). It is suggested that alpacas can feel heat stress in summer (HSI = 139.4), which could influence higher cortisol levels in the distal segment. The wool cortisol level was higher in the rump samples than the shoulder ones. Therefore, it is essential in future studies that wool samples from all tested animals should be completed from the same body region. Differences among age and sex groups were also observed. Wool cortisol level was higher in older animals, as differences between age groups were observed in samples from the rump in the distal and proximal segments (distal, the rump younger*older: P < 0.001; η2 = 0.321; proximal, the rump older*younger: P = 0.007; η2 = 0.195). Males showed higher cortisol levels than females, as a difference between sexes was observed in samples from the rump in the proximal segment (P = 0.001, η2 = 0.271). This study emphasizes that various factors may significantly influence wool cortisol levels, which can be helpful in alpacas' welfare estimation using this hormonal indicator as a noninvasive long-term stress assessment method.

Seasonal Hair Glucocorticoid Fluctuations in Wild Mice (Phyllotis darwini) within a Semi-Arid Landscape in North-Central Chile

Mammals in drylands face environmental challenges exacerbated by climate change. Currently, human activity significantly impacts these environments, and its effects on the energy demands experienced by individuals have not yet been determined. Energy demand in organisms is managed through elevations in glucocorticoid levels, which also vary with developmental and health states. Here, we assessed how anthropization, individual characteristics, and seasonality influence hair glucocorticoid concentration in the Darwin's leaf-eared mouse (Phyllotis darwini) inhabiting two areas with contrasting anthropogenic intervention in a semi-arid ecosystem of northern Chile. Hair samples were collected (n = 199) to quantify hair corticosterone concentration (HCC) using enzyme immunoassays; additionally, sex, body condition, and ectoparasite load were recorded. There were no differences in HCC between anthropized areas and areas protected from human disturbance; however, higher concentrations were recorded in females, and seasonal fluctuations were experienced by males. The results indicate that animals inhabiting semi-arid ecosystems are differentially stressed depending on their sex. Additionally, sex and season have a greater impact on corticosterone concentration than anthropogenic perturbation, possibly including temporal factors, precipitation, and primary production. The influence of sex and seasonality on HCC in P. darwini make it necessary to include these variables in future stress assessments of this species.

Associations between glucocorticoids and habitat selection reflect daily and seasonal energy requirements

BACKGROUND

Glucocorticoids are often associated with stressful environments, but they are also thought to drive the best strategies to improve fitness in stressful environments. Glucocorticoids improve fitness in part by regulating foraging behaviours in response to daily and seasonal energy requirements. However, many studies demonstrating relationships between foraging behaviour and glucocorticoids are experimental, and few observational studies conducted under natural conditions have tested whether changing glucocorticoid levels are related to daily and seasonal changes in energy requirements.

METHODS

We integrated glucocorticoids into habitat selection models to test for relationships between foraging behaviour and glucocorticoid levels in elk (Cervus canadensis) as their daily and seasonal energy requirements changed. Using integrated step selection analysis, we tested whether elevated glucocorticoid levels were related to foraging habitat selection on a daily scale and whether that relationship became stronger during lactation, one of the greatest seasonal periods of energy requirement for female mammals.

RESULTS

We found stronger selection of foraging habitat by female elk with elevated glucocorticoids (eß = 1.44 95% CI 1.01, 2.04). We found no difference in overall glucocorticoid levels after calving, nor a significant change in the relationship between glucocorticoids and foraging habitat selection at the time of calving. However, we found a gradual increase in the relationship between glucocorticoids and habitat selection by female elk as their calves grew over the next few months (eß = 1.01, 95% CI 1.00, 1.02), suggesting a potentially stronger physiological effect of glucocorticoids for elk with increasing energy requirements.

CONCLUSIONS

We suggest glucocorticoid-integrated habitat selection models demonstrate the role of glucocorticoids in regulating foraging responses to daily and seasonal energy requirements. Ultimately, this integration will help elucidate the implications of elevated glucocorticoids under natural conditions.

Hair cortisol concentration in finishing pigs on commercial farms: variability between pigs, batches, and farms

Hair cortisol is a stress indicator and could be used to assess the pigs' exposure to stressors in the weeks/months prior to non-invasive hair sampling. The main aim of this study was to describe the hair cortisol concentration (HCC) variability between individuals within a batch, between farms and between batches within a farm. The secondary aim was to determine how the number of sampled pigs influences the characterization of HCC within a batch. Twenty farrow-to-finish pig farms were recruited considering the diversity of their management practices and health status (data collected). Hair was sampled in two separate batches, 8 months apart. The necks of 24 finishing pigs were clipped per batch the week prior to slaughter. To describe the variability in HCC, an analysis of the variance model was run with three explanatory variables (batch, farm and their interaction). To identify farm clusters, a principal component analysis followed by a hierarchical clustering was carried out with four active variables (means and standard deviations of the two batches per farm) and 17 supplementary variables (management practices, herd health data). We determined how the number of sampled pigs influenced the characterization of HCC within a batch by selecting subsamples of the results. HCC ranged from 0.4 to 121.6 pg/mg, with a mean of 25.9 ± 16.2 pg/mg. The variability in HCC was mainly explained by differences between pigs (57%), then between farms (24%), between batches within the same farm (16%) and between batches (3%). Three clusters of farms were identified: low homogeneous concentrations (n = 3 farms), heterogeneous concentrations with either higher (n = 7) or lower (n = 10) HCC in batch 2 than in batch 1. The diversity of management practices and health statuses allowed to discuss hypotheses explaining the HCC variations observed. We highlighted the need to sample more than 24 pigs to characterize HCC in a pig batch. HCC differences between batches on six farms suggest sampling pigs in more than one batch to describe the HCC at the farm level. HCC variations described here confirm the need to study its links with exposure of pigs to stressors.

Robust Responses of Female Caribou to Changes in Food Supply

AbstractUngulates can respond to changes in food supply by altering foraging behavior, digestive function, and metabolism. A multifaceted response to an environmental change is considered robust. Short seasons of plant growth make herbivores sensitive to changes in food supply because maintenance and production must be accomplished in less time with fewer options in a more fragile response. Caribou live at high latitudes where short summers constrain their response to changes in food supply. We measured the ability of female caribou to resist and tolerate changes in the quality and quantity of their food supply during winter and summer. Caribou resisted changes in food abundance and quality by changing food intake and physical activity with changes in daily temperature within each season. Peak food intake rose by 134% from winter pregnancy to summer lactation (98 vs. 229 g kg-0.75 d-1), as digestible requirements to maintain the body increased by 85% for energy (1,164 vs. 2,155 kJ kg-0.75 d-1) and by 266% for N (0.79 vs. 2.89 g N kg-0.75 d-1). Caribou required a diet with a digestible content of 12 kJ g-1 and 0.8% N in pregnancy, 18 kJ g-1 and 1.9% N in early lactation, and 11 kJ g-1 and 1.2% N in late lactation, which corresponds with the phenology of the wild diet. Female caribou tolerated restriction of ad lib. food intake to 58% of their energy requirement (680 vs. 1,164 kJ kg-0.75 d-1) during winter pregnancy and to 84% of their energy requirement (1,814 vs. 2,155 kJ kg-0.75 d-1) during summer lactation without a change in stress level, as indicated by fecal corticosterone concentration. Conversely, caribou can respond to increased availability of food with a spare capacity to process digestible energy and N at 123% (2,642 vs. 2,155 kJ kg-0.75 d-1) and 145% (4.20 vs. 2.89 g N kg-0.75 d-1) of those respective requirements during lactation. Robust responses to changes in food supply allow caribou to sustain reproduction, which would buffer demographic response. However, herds may decline when thresholds of behavioral resistance and physiological tolerance are frequently exceeded. Therefore, the challenge for managing declining populations of caribou and other robust species is to identify declines in robustness before their response becomes fragile.

Technical validation and a comparison of two methods to quantify individual levels of glucocorticoids in Alpine marmot hair

Quantification of cortisol concentration in hair has become a promising conservation tool for non-invasive monitoring of "stress" in wild populations, yet this method needs to be carefully validated for each species. The goals of the study were:•Immunologically validate two methods (study 1 and 2 respectively) to extract and quantify cortisol in the hair of wild Alpine marmots.•Compare the amount of cortisol extracted from hair samples using two methods i.e. cut into fine pieces (study 1) and hair samples pulverized using a ball mill (study 2).•Determine the extent to which methods in study 2 could provide individual specific hair cortisol (HC) measures when samples were taken from the same body location. Within and between individual variations in HC levels were examined from multiple hair samples from 14 subjects in study 2. We evaluated if inter-individual variations in HC levels could be explained by sex and age.At least twice the amount of cortisol was obtained per g/hair when samples were pulverized in a ball mill prior to extraction compared to when cut into pieces. Our methods demonstrated intra-individual consistency in HC at a given time point: inter-individual variation in HC was three times larger than within individual variance. Sex and age did not impact HC levels.

An integrative and multi-indicator approach for wildlife health applied to an endangered caribou herd

Assessing wildlife health in remote regions requires a multi-faceted approach, which commonly involves convenient samplings and the need of identifying and targeting relevant and informative indicators. We applied a novel wildlife health framework and critically assessed the value of different indicators for understanding the health status and trends of an endangered tundra caribou population. Samples and data from the Dolphin and Union caribou herd were obtained between 2015 and 2021, from community-based surveillance programs and from captured animals. We documented and categorized indicators into health determinants (infectious diseases and trace elements), processes (cortisol, pathology), and health outcomes (pregnancy and body condition). During a recent period of steep population decline, our results indicated a relatively good body condition and pregnancy rates, and decreasing levels of stress, along with a low adult cow survival. We detected multiple factors as potential contributors to the reduced survival, including Brucella suis biovar 4, Erysipelothrix rhusiopathiae and lower hair trace minerals. These results remark the need of targeted studies to improve detection and investigations on caribou mortalities. We also identified differences in health indicators between captured and hunter sampled caribou, highlighting the importance of accounting for sampling biases. This integrative approach that drew on multiple data sources has provided unprecedented knowledge on the health in this herd and highlights the value of documenting individual animal health to understand causes of wildlife declines.

Hair glucocorticoids are not a historical marker of stress - Exploring the time-scale of corticosterone incorporation into hairs in a rat model

Hair glucocorticoids are increasingly popular biomarkers, used across numerous research fields, and studied species, as a measure of stress. Although they are suggested to be a proxy of the average HPA axis activity spanning a period of weeks or months into the past, this theory has never been tested. In the present study, adrenalectomized rats with no endogenous (adrenal) glucocorticoid production were used to study how circulating glucocorticoid levels would be reflected in the glucocorticoid levels found in hair samples. By dosing the animals daily with high levels of corticosterone for seven days, while sampling hairs before, during, and after treatments, a timeline for glucocorticoid uptake into hairs was constructed. This kinetic profile was compared to two hypothetical models, and the theory that hair glucocorticoids are a record of historical stress had to be rejected. Corticosterone concentrations in hairs were found to increase within three hours of the first injection, the highest concentrations were found on the seventh day of treatments, and the decrease in concentrations post-treatment suggests rapid elimination. We speculate that hair glucocorticoid levels can only be used to characterize a stress-response for a few days following a postulated stressor. An updated model, where glucocorticoids diffuse into, along, and out of hairs needs to be adopted to reconcile the experimentally obtained data. The inescapable consequence of this updated model is that hair glucocorticoids become a marker of - and can only be used to study - recent, or ongoing, stress, as opposed to historical events, weeks or months in the past.

Hair Cortisol Concentrations in Feral Horses and the Influence of Physiological and Social Factors

Cortisol is a glucocorticoid hormone produced during activation of the hypothalamic-pituitary-adrenal axis (HPA) in response to psychological or physiological demands. High amounts of circulating cortisol can be found in individuals experiencing energetically demanding physiological events, such as pregnancy, lactation, injury, or starvation, but, also, in individuals who may have less obvious HPA activation from social situations. The feral horse population on Sable Island (Nova Scotia, Canada) provides an opportunity to look at hair cortisol concentration (HCC) as a proxy for circulating cortisol concentration to better understand physiological correlates. The horse's complex social structure also allows us to look at how the population and group structure may influence HPA activation. Hair samples (n = 282) were analyzed from 113 females and 135 males. Females with dependent offspring (foals) had higher HCC than those females without dependent offspring (p = 0.005). Horses in poor body condition were also more likely to have higher HCC (females: p < 0.001, males: p = 0.028); females had greater variation in the body condition index (BCI), which also correlated with foal production. In general, the top-ranked models describing female cortisol levels included age, BCI, presence of a foal, as well as social measures such as harem size and the number of bachelors in the vicinity. The top model describing male cortisol levels included age, BCI, and year of collection only, and the number of bachelors in the home range appeared in subsequent, though still high-ranked, models. Among the variables not of direct interest, we found some significant results relating to hair color and hair texture. Differences in HCC patterns between feral and domestically kept horses (e.g., age and sex) are likely linked to periods of resource limitations, particularly for individuals experiencing energetically demanding processes such as reproduction, illness/parasitism, or related to experiencing the full range of social and reproductive behaviors.

Variation of hair cortisol in two herds of migratory caribou (Rangifer tarandus): implications for health monitoring

Migratory caribou (Rangifer tarandus sspp.) is an ecotype of conservation concern that is experiencing increased cumulative stressors associated with rapid climate change and development in Arctic Canada. Increasingly, hair cortisol concentrations (HCCs) are being used to monitor seasonal hypothalamic-pituitary-adrenal axis activity of ungulate populations; yet, the effect of key covariates for caribou (sex, season, sampling source, body location) are largely unknown. The objectives of this research were 4-fold: first, we assessed the impact of body location (neck, rump) sampling sites on HCC; second, we assessed key covariates (sex, sampling method, season) impacting HCCs of caribou; third, we investigated inter-population (Dolphin and Union (DU), Bluenose-East (BNE)) and inter-annual differences in HCC and fourth, we examined the association between HCCs and indices of biting insect activity on the summer range (oestrid index, mosquito index). We examined hair from 407 DU and BNE caribou sampled by harvesters or during capture-collaring operations from 2012 to 2020. Linear mixed-effect models were used to assess the effect of body location on HCC and generalized least squares regression (GLS) models were used to examine the impacts of key covariates, year and herd and indices of biting insect harassment. HCC varied significantly by body location, year, herd and source of samples (harvester vs capture). HCC was higher in samples taken from the neck and in the DU herd compared with the BNE, decreased linearly over time and was higher in captured versus hunted animals (P < 0.05). There was no difference in HCC between sexes, and indices of biting insect harassment in the previous year were not significantly associated with HCC. This study identifies essential covariates impacting the HCC of caribou that must be accounted for in sampling, monitoring and data interpretation.

Evaluation of physiological stress in free-ranging bears: current knowledge and future directions

Stress responses, which are mediated by the neurogenic system (NS) and hypothalamic-pituitary-adrenal (HPA) axis help vertebrates maintain physiological homeostasis. Fight-or-flight responses are activated by the NS, which releases norepinephrine/noradrenaline and epinephrine/adrenaline in response to immediate stressors, whilst the HPA axis releases glucocorticoid hormones (e.g. cortisol and corticosterone) to help mitigate allostatic load. There have been many studies on stress responses of captive animals, but they are not truly reflective of typical ranges or the types of stressors encountered by free-ranging wildlife, such as responses and adaptation to environmental change, which are particularly important from a conservation perspective. As stress can influence the composition of age and sex classes of free-ranging populations both directly and indirectly, ecological research must be prioritised towards more vulnerable taxa. Generally, large predators tend to be particularly at risk of anthropogenically driven population declines because they exhibit reduced behavioural plasticity required to adapt to changing landscapes and exist in reduced geographic ranges, have small population sizes, low fecundity rates, large spatial requirements and occupy high trophic positions. As a keystone species with a long history of coexistence with humans in highly anthropogenic landscapes, there has been growing concern about how humans influence bear behaviour and physiology, via numerous short- and long-term stressors. In this review, we synthesise research on the stress response in free-ranging bear populations and evaluate the effectiveness and limitations of current methodology in measuring stress in bears to identify the most effective metrics for future research. Particularly, we integrate research that utilised haematological variables, cardiac monitors and Global Positioning System (GPS) collars, serum/plasma and faecal glucocorticoid concentrations, hair cortisol levels, and morphological metrics (primarily skulls) to investigate the stress response in ursids in both short- and long-term contexts. We found that in free-ranging bears, food availability and consumption have the greatest influence on individual stress, with mixed responses to anthropogenic influences. Effects of sex and age on stress are also mixed, likely attributable to inconsistent methods. We recommend that methodology across all stress indicators used in free-ranging bears should be standardised to improve interpretation of results and that a wider range of species should be incorporated in future studies.

Stress in wildlife: comparison of the stress response among domestic, captive, and free-ranging animals

The stress response, which involves joint activity of the nervous and endocrine systems, is one of the basic adaptive mechanisms that ensures the survival of the individual. The activation of the sympathetic nervous system, the sympathetic-adrenal-medullary axis, and the hypothalamic-pituitary-adrenal axis enables organisms to respond to endogenous and exogenous challenges. Repeated short-term stress leads to long-term stress, which disrupts physiological homeostasis. Unlike domestic animals, wild animals are not protected from environmental and weather influences or treated for diseases. In addition, climate change, habitat fragmentation and loss, and urban stressors (such as light, noise and chemical pollution; xenobiotics; traffic; and buildings) affect individual wildlife and populations. In this review, we have attempted to depict the magnitude of the stress response in wildlife and related domestic animals as well as in captive and free-ranging animals. The intensity of the stress response can be estimated by determining the concentration of glucocorticoids in body fluids, tissues, and excreta. A comparison of results from different studies suggests that domestic animals have lower fecal and hair glucocorticoid concentrations than related wild animals. Additionally, fecal and hair glucocorticoid concentrations in captive animals are higher than in free-ranging animals of the same species. As there are limited data on this topic, we cannot draw definitive conclusions about glucocorticoid concentration and stress response. Further studies are needed to clarify these issues.

Assessing chronic stress in wild mammals using claw-derived cortisol: a validation using European badgers (Meles meles)

Measuring stress experienced by wild mammals is increasingly important in the context of human-induced rapid environmental change and initiatives to mitigate human-wildlife conflicts. Glucocorticoids (GC), such as cortisol, mediate responses by promoting physiological adjustments during environmental perturbations. Measuring cortisol is a popular technique; however, this often reveals only recent short-term stress such as that incurred by restraining the animal to sample blood, corrupting the veracity of this approach. Here we present a protocol using claw cortisol, compared with hair cortisol, as a long-term stress bio-indicator, which circumvents this constraint, where claw tissue archives the individual's GC concentration over preceding weeks. We then correlate our findings against detailed knowledge of European badger life history stressors. Based on a solid-phase extraction method, we assessed how claw cortisol concentrations related to season and badger sex, age and body-condition using a combination of generalized linear mixed models (GLMM) (n = 668 samples from 273 unique individuals) followed by finer scale mixed models for repeated measures (MMRM) (n = 152 re-captured individuals). Claw and hair cortisol assays achieved high accuracy, precision and repeatability, with similar sensitivity. The top GLMM model for claw cortisol included age, sex, season and the sex*season interaction. Overall, claw cortisol levels were significantly higher among males than females, but strongly influenced by season, where females had higher levels than males in autumn. The top fine scale MMRM model included sex, age and body condition, with claw cortisol significantly higher in males, older and thinner individuals. Hair cortisol was more variable than claw; nevertheless, there was a positive correlation after removing 34 outliers. We discuss strong support for these stress-related claw cortisol patterns from previous studies of badger biology. Given the potential of this technique, we conclude that it has broad application in conservation biology.

Determination of hair cortisol in horses: comparison of immunoassay vs LC-HRMS/MS

The measure of hair cortisol concentration (HCC) is becoming an emerging approach to monitor mid-/long-term stress in animals, so it is more and more important to develop accurate and reliable methods. In the light of this, the aim of the present study was to compare mane HCCs of 47 horses with different managements, by means of an immunoassay (ELISA) and liquid chromatography coupled to hybrid high-resolution mass spectrometry (LC-HRMS/MS). After the washing step, the ground hair was extracted with methanol. The extract was evaporated and redissolved in two different aqueous solutions, depending on the detection technique. The methods were validated according to EMA guideline for bioanalytical method validation, in the range 2–50 pg mg⁻¹ (ELISA) and 1–100 pg mg⁻¹ (LC-HRMS/MS). Satisfactory quantitative performances were obtained for both of the approaches, but this latter demonstrated better precision. The detected concentrations in real samples were encompassing the range 1.3–8.8 pg mg⁻¹ and 2.0–17.9 pg mg⁻¹ by means of LC-HRMS/MS and ELISA, respectively. Overall, HCCs measured with ELISA technique were 1.6 times higher. The overestimation of immunoassay results might be caused by cross-reactivity phenomena of laboratory reagents and other structurally similar hormones present in the mane.

Hair cortisol concentration reflects the life cycle and management of grey wolves across four European populations

The grey wolf (Canis lupus) persists in a variety of human-dominated landscapes and is subjected to various legal management regimes throughout Europe. Our aim was to assess the effects of intrinsic and methodological determinants on the hair cortisol concentration (HCC) of wolves from four European populations under different legal management. We determined HCC by an enzyme-linked immune assay in 259 hair samples of 133 wolves from the Iberian, Alpine, Dinaric-Balkan, and Scandinavian populations. The HCC showed significant differences between body regions. Mean HCC in lumbar guard hair was 11.6 ± 9.7 pg/mg (range 1.6–108.8 pg/mg). Wolves from the Dinaric-Balkan and Scandinavian populations showed significantly higher HCC than Iberian wolves, suggesting that harvest policies could reflected in the level of chronic stress. A significant negative relationship with body size was found. The seasonal, sex and age patterns are consistent with other studies, supporting HCC as a biomarker of chronic stress in wolves for a retrospective time frame of several weeks. Our results highlight the need for standardization of sampling and analytical techniques to ensure the value of HCC in informing management at a continental scale.

Hair cortisol and dehydroepiandrosterone sulfate concentrations in healthy beef calves from birth to 6 months of age

Cortisol (C) and dehydroepiandrosterone (DHEA) are recognized as the main fetal steroids, and they are likely to influence fetal development and have long-term effects on newborn hypothalamic-pituitary-adrenal axis (HPA) function. DHEA is often measured as its sulfates and expressed as DHEA-S. Hair analysis represents a promising methodological approach for the non-invasive measurement of steroids, allowing for a retrospective analysis of the total exposure to steroids over time, and avoiding the influence of acute events or circadian fluctuations. Hair cortisol and DHEA concentrations have been investigated in cows, but no studies have been performed on calves. The object of this study was to evaluate hair cortisol (HC) and hair DHEA-S (HDHEA-S) concentrations in beef calves from birth to six months of age. Hair samples of 12 beef calves (seven males, five females) were firstly collected at birth (T1) and then every three weeks up to six months of age (T2-T10), collecting only the re-grown hair. HC and HDHEA-S were analyzed by radioimmunoassay (RIA). Calves sex, weight and APGAR score were registered immediately after birth. Statistical analysis revealed that both HC and HDHEA-S were influenced by sampling time (P < 0.001). HC concentrations were higher at T1 compared to all subsequent samplings (T2-T10, P < 0.01); HC concentrations were higher at T2 compared to T4-T10 (P < 0.01), while no further changes were detected from T3 onward. Higher HDHEA-S concentrations were registered at T1, T2 and T3 compared to all the other samplings (P < 0.01). No correlation was found between hair concentrations of both steroids and calf sex or birthweight. APGAR score was negatively correlated only with HC at birth (P < 0.05). These data demonstrate that C and DHEA-S are quantifiable in the hair of calves and are influenced by their age. The higher HC detected at birth (T1) probably reflects the high serum C concentrations present late in pregnancy and increased by the fetal HPA axis, by which parturition is initiated in cows. The highest HDHEA-S at birth (T1) in calves indicates that the largest amounts of DHEA and its sulfates are produced during fetal development. Moreover, the findings of higher HC at three weeks after birth and of higher HDHEA-S until six weeks after birth, suggest that C and DHEA secretion continues also beyond birth, and that these steroids could be involved in the events occurring during the challenging first weeks of age in the calf.

Analysis of hair steroid hormones in polar bears (Ursus maritimus) via liquid chromatography-tandem mass spectrometry: comparison with two immunoassays and application for longitudinal monitoring in zoos

Analysis of hair cortisol concentrations (HCCs) is a promising method for monitoring long-term stress in mammals. However, previous measurements of HCCs in polar bears (Ursus maritimus) have yielded highly variable results, which are likely due to different methodological approaches. In this study, hair samples of zoo-housed polar bears were analyzed for cortisol with two independent immunoassays [an enzyme-linked immunoassay (EIA) and a chemiluminescence assay (CLIA)] and liquid chromatography-tandem mass spectrometry (LC-MS/MS). HCC measurements depended significantly on assay type applied, sample processing (cutting vs. powdering hair) and their interaction. Best agreement was observed between LC-MS/MS and CLIA (R² = 0.81 for powdered hair) and sample processing had a minor, albeit significant, effect on obtained HCC measurements in these assays (R² > 0.9). EIA measurements were consistently higher than with the other assays. HCC measurement was validated biologically for CLIA and LC-MS/MS in one male polar bear that experienced considerable stress for a prolonged period of time (> 18 weeks). Subsequently, by using the validated LC-MS/MS the measurement of cortisol could be complemented by the analysis of other steroids including cortisone, testosterone and progesterone levels from hair samples collected over a 9-month period (5-13 months) from six zoo-housed polar bears (five males, one female). No seasonal steroid variation was observed except in male progesterone levels. For all steroids except cortisone, a strong body region effect (neck or paw) was observed. Cortisol and cortisone, as well as progesterone and testosterone, concentrations were positively correlated. We show that hair steroid concentrations can be used to longitudinally measure stress and reproductive hormone axes in polar bears. The data established herein provide important basic information regarding methodology and study design for assessing hair steroid hormones.

Investigation of keratinase digestion to improve steroid hormone extraction from diverse keratinous tissues

Monitoring the physiology of wild populations presents many technical challenges. Blood samples, long the gold standard of wildlife endocrinology studies, cannot always be obtained. The validation and use of non-plasma samples to obtain hormone data have greatly improved access to more integrated information about an organism's physiological state. Keratinous tissues like skin, hair, nails, feathers, or baleen store steroid hormones in physiologically relevant concentrations, are stable across decades, and can be used to retrospectively infer physiological state at prior points in time. Most protocols for steroid extraction employ physical pulverization or cutting of the sample, followed by mixing with a solvent. Such methods do produce repeatable and useful data, but low hormone yield and detectability issues can complicate research on small or rare samples. We investigated the use of keratinase, an enzyme that breaks down keratin, to improve the extraction and yield of corticosterone from vertebrate keratin tissues. Corticosterone content of keratinase-digested extracts were compared to non-keratinase extracts for baleen from three species of whale (blue, Balaenoptera musculus; bowhead, Balaena mysticetus; southern right, SRW; Eubalaena australis), shed skin from two reptiles (tegu lizard, Salvator merianae; narrow-headed garter snake, Thamnophis rufipunctatus), hair from arctic ground squirrel (AGS; Urocitellus parryii), feathers from Purple Martins (PUMA; Progne subis), and spines from the short-beaked echidna (Tachyglossus aculeatus). We tested four starting masses (10, 25, 50, 100 mg) for each sample; digestion was most complete in the 10 and 25 mg samples. A corticosterone enzyme immunoassay (EIA) was validated for all keratinase-digested extracts. In all sample types except shed skin from reptiles, keratinase digestion improved hormone yield, with PUMA feathers and blue whale baleen having the greatest increase in apparent corticosterone content (100% and 66% more hormone, respectively). The reptilian shed skin samples did not benefit from keratinase digestion, actually yielding less hormone than controls. With further optimization and refinement, keratinase digestion could greatly improve yield of steroid hormones from various wildlife epidermal tissue types, allowing more efficient use of samples and ultimately improving understanding of the endocrine physiology of wild populations.

Inter- and intra-specific variation in hair cortisol concentrations of Neotropical bats

Quantifying hair cortisol has become popular in wildlife ecology for its practical advantages for evaluating stress. Before hair cortisol levels can be reliably interpreted, however, it is key to first understand the intrinsic factors explaining intra- and inter-specific variation. Bats are an ecologically diverse group of mammals that allow studying such variation. Given that many bat species are threatened or have declining populations in parts of their range, minimally invasive tools for monitoring colony health and identifying cryptic stressors are needed to efficiently direct conservation efforts. Here we describe intra- and inter-specific sources of variation in hair cortisol levels in 18 Neotropical bat species from Belize and Mexico. We found that fecundity is an important ecological trait explaining inter-specific variation in bat hair cortisol. Other ecological variables such as colony size, roost durability and basal metabolic rate did not explain hair cortisol variation among species. At the individual level, females exhibited higher hair cortisol levels than males and the effect of body mass varied among species. Overall, our findings help validate and accurately apply hair cortisol as a monitoring tool in free-ranging bats.

Testosterone levels in hair of free-ranging male northern fur seals (Callorhinus ursinus) in relation to sampling month, age class and spermatogenesis

Information about the reproductive status of free-ranging pinnipeds provides useful insight into their population dynamics, which is essential to their management and conservation. To determine the reproductive status of individual animals, blood sampling is often required despite being impractical to collect in open water. Hair as an endocrine marker has been used to less invasively assess the reproductive status of terrestrial animals. However, it is unknown whether pinniped reproductive status can be assessed from hair samples. Here, we examine testosterone levels in hair obtained from 57 male northern fur seals and used it to compare their age class and spermatogenesis during the non-breeding season off Hokkaido. We isolated testosterone from the samples using gas chromatography and measured testosterone levels using time-resolved fluoroimmunoassay. Testosterone levels in hair increased towards the breeding season. In May, testosterone levels were the highest in seals aged between 4 and 7 years, followed by those over the age of 8 years and under the age of 4 years. Spermatids, the final phase of spermatogenesis, were present in the seals sampled between April and June, even though testosterone levels were low in April. The seals with spermatids in May showed the highest testosterone levels. Our results demonstrate that seals with higher testosterone levels in May are likely to be mature males (≥4 years). Since hair can be collected using biopsy darts in the field, it will be possible to less invasively determine testosterone levels of male seals in the future.

Qiviut cortisol reflects hypothalamic-pituitary-adrenal axis activity in muskoxen (Ovibos moschatus)

Muskoxen (Ovibos moschatus) are increasingly exposed to a broad diversity of stressors in their rapidly changing Arctic environment. There is an urgent need to develop validated tools to monitor the impact of these stressors on the hypothalamic-pituitary-adrenal (HPA) axis activity of muskoxen to help inform conservation actions. Here, we evaluated whether muskox qiviut (dense wooly undercoat) cortisol accurately reflects changes in HPA axis activity. Two repeated pharmacological challenges, involving weekly administrations of saline (control group) or adrenocorticotropic hormone (ACTH) during five consecutive weeks, were done on captive muskoxen, in winter (no hair growth) and summer (maximum hair growth). Pre-challenge qiviut cortisol levels were significantly higher in the shoulder than in the neck, but neither differed from rump concentrations. Qiviut cortisol levels significantly increased (p < 0.001) in response to the administration of ACTH during the hair growth phase, but not in the absence of growth (p = 0.84). Cortisol levels in the qiviut segment grown during the summer challenge increased significantly over a six-month period in the ACTH-injected muskoxen with a similar trend occurring in the control animals. Finally, cortisol levels in shed qiviut were significantly higher and not correlated to those of fully grown qiviut shaved three months earlier. Our results show that cortisol is deposited in qiviut during its growth and that qiviut cortisol can thus be used as an integrated measure of HPA axis activity over the period of the hair's growth. Differences in qiviut cortisol across body regions, significant differences in qiviut segments over time, and differences between shed qiviut versus unshed qiviut, highlight the importance of consistent design and methodology for sample collection and analyses in order to account for sources of variation when using qiviut cortisol as a biomarker of HPA axis activity in muskoxen.

Cortisol levels in blood and hair of unanesthetized grizzly bears (Ursus arctos) following intravenous cosyntropin injection

Hair cortisol concentration (HCC) is being used increasingly to evaluate long‐term stress in many mammalian species. Most of the cortisol is assumed to passively diffuse from circulating blood into hair follicles and gradually accumulate in growing hair. However, our research with free‐ranging grizzly bears (Ursus arctos) suggests HCC increases significantly within several hours following capture, a time too brief to be explained by this mechanism alone. In this study with captive grizzly bears, we sought to determine if a brief spike in blood cortisol concentration, thus mimicking a single stressful event, would cause an increase in HCC over a 7‐day period. To do this, we administered a single intravenous dose (5 μg/kg) of cosyntropin to three captive unanaesthetised adult female grizzly bears on two occasions, during April when hair growth was arrested and during August when hair was growing. In both trials, the cosyntropin caused a two‐fold or greater increase in serum cortisol levels within 1 hr but did not appear to influence HCC at 1, 48, and 168 hr following cosyntropin administration. We conclude the cosyntropin‐induced cortisol spike was likely insignificant when compared to the adrenocortical response that occurs in free‐ranging bears when captured. We suggest further study with a larger sample of captive bears to evaluate the combined effects of anaesthesia and multiple doses of cosyntropin administered over several hours would better simulate the adrenocortical response of free‐ranging grizzly bears during capture.

Long-term stress level in a small mammal species undergoing range expansion

Rapid climate change is currently altering species distribution ranges. Evaluating the long-term stress level in wild species undergoing range expansion may help better understanding how species cope with the changing environment. Here, we focused on the white-footed mouse (Peromyscus leucopus), a widespread small mammal species in North-America whose distribution range is rapidly shifting northward. We evaluated long-term stress level in several populations of P. leucopus in Quebec (Canada), from the northern edge of the species distribution to more core populations in Southern Quebec. We first tested the hypothesis that populations at the range margin are under higher stress than more established populations in the southern region of our study area. We then compared four measures of long-term stress level to evaluate the congruence between these commonly used methods. We did not detect any significant geographical trend in stress level across our study populations of P. leucopus. Most notably, we found no clear congruence between the four measures of stress level we used, and conclude that these four commonly used methods are not equivalent, thereby not comparable across studies.

Fecal glucocorticoid metabolites reflect hypothalamic-pituitary-adrenal axis activity in muskoxen (Ovibos moschatus)

Muskoxen (Ovibos moschatus), a taxonomically unique Arctic species, are increasingly exposed to climate and other anthropogenic changes. It is critical to develop and validate reliable tools to monitor their physiological stress response in order to assess the impacts of these changes. Here, we measured fecal glucocorticoid metabolite (FGM) levels in response to the administration of adrenocorticotropic hormone (ACTH) in the winter (1 IU/kg) and summer (2 IU/kg) using two enzyme immunoassays, one targeting primarily cortisol and the other targeting primarily corticosterone. Fecal cortisol levels varied substantially within and among individuals, and none of the animals in either challenge showed an increase in fecal cortisol following the injection of ACTH. By contrast, two of six (winter) and two of five (summer) muskoxen showed a clear response in fecal corticosterone levels (i.e., maximal percentage increase as compared to time 0 levels > 100%). Increases in fecal corticosterone post-ACTH injection occurred earlier and were of shorter duration in the summer than in the winter and fecal corticosterone levels were, in general, lower during the summer. These seasonal differences in FGM responses may be related to the use of different individuals (i.e., influence of sex, age, social status, etc.) and to seasonal variations in the metabolism and excretion of glucocorticoids, intestinal transit time, voluntary food intake, and fecal output and moisture content. Results from this study support using FGMs as a biomarker of hypothalamic–pituitary–adrenal axis activity in muskoxen, advance our understanding of the physiological adaptations of mammals living in highly seasonal and extreme environments such as the Arctic, and emphasize the importance of considering seasonality in other species when interpreting FGM levels.

The Effect of Body Region on Hair Cortisol Concentration in Common Marmosets (Callithrix jacchus)

Common marmosets (Callithrix jacchus) are a valuable research model for the study of neuroscience and the biologic impact of aging due to their adaptivity, physiologic characteristics, and ease of handling for experimental manipulations. Quantification of cortisol in hair provides a noninvasive, retrospective biomarker of hypothalamics-pituitary-adrenal (HPA) axis activity and information on animal wellbeing, including responses to environmental and social stimuli. To obtain valid and reliable measurements of long-term HPA activity, we investigated the variability of cortisol concentration in the hair depending on the body region of marmosets. Hair was collected from the back and tail of 9 adult common marmosets during annual health screenings (male n = 3; female n = 6) and these samples were analyzed for cortisol via methanol extraction and enzyme immunoassay. We found that hair cortisol concentration differed between the tail and back regions, with the tail samples having a significantly higher cortisol concentration. These results indicate intraindividual and interindividual comparisons of hair cortisol concentration should use hair obtained from the same body region in marmosets.

Controlled experiments to explore the use of a multi-tissue approach to characterizing stress in wild-caught Pacific halibut (Hippoglossus stenolepis)

The integration of multiple tissues in physiological and ecological analyses can enhance methodological approaches, increase applications for data and extend interpretation of results. Previous investigations of the stress response in fish have focused primarily on cortisol levels in a single matrix-blood plasma-which confines interpretations of cortisol levels to a short temporal frame. Epidermal mucus has been proposed as an alternative or complement to plasma that may provide a view to cortisol levels over a different temporal window allowing comparative assessment. Here, we explore the potential for multi-tissue cortisol analysis using both plasma and epidermal mucus in Pacific halibut (Hippoglossus stenolepis). The relative timing at which cortisol increased and decreased in the two matrices as well as cortisol concentrations at estimated peak levels were compared in two trials after (i) inducing cortisol synthesis by adrenocorticotropic hormone (ACTH_1-24) administration and (ii) inducing cortisol elimination using cortisol (hydrocortisone, 98%) injection. The ACTH treatment elicited a peak plasma cortisol response approximately 12 hours post-injection, while mucus cortisol concentrations peaked later at approximately 62 hours post-injection. Exogenous cortisol treatments suggested relatively little transfer of cortisol from plasma to mucus, potentially reflecting differential effects of endogenous and exogenous cortisol. Our results suggest the potential utility of mucus as a sampling matrix that provides an extended window for detection of the stress response as compared to plasma. Results also suggest the utility of a multi-tissue approach to cortisol analysis with potential applications to applied fisheries research. Increased understanding of the relative scale of the cortisol response to stress (e.g. capture) will allow researchers and managers to better interpret the physiological condition and survival outcome of fish subjected to regulatory discard.

Degradation of Temminck's pangolin (Smutsia temminckii) scales with a keratinase for extraction of reproductive steroid hormones

Hormone monitoring in keratinous tissues has become increasingly popular. The insoluble keratin materials are generally pulverised before hormone extraction; however, this is difficult for thicker keratin structures like baleen plates or hooves. A new method, involving the use of keratinase, allows enzymatic digestion of keratin and hormone analysis in the resulting suspension. Pangolins are unique mammals covered in keratinous scales, which are one of the reasons these animals are extensively trafficked. This study aimed to investigate the suitability of Temminck's pangolin scales as hormone matrix for quantifying reproductive steroids. A protocol was developed to digest scales with a keratinase before measuring hormone concentrations. This method can be used to investigate the reproductive endocrinology of Temminck's pangolins but may also be extended to the other extant pangolin species.•Keratinase digests Temminck's pangolin scales and reproductive steroid metabolite concentrations are measurable in the resulting suspension.•Isopropanol is an ideal washing solvent for scales to remove surface contaminants and scale sample mass should be standardised to allow comparisons.•Any section of a scale and scales from any pangolin body region can be used as samples for hormone quantification.

Is it getting in the hair? - Cortisol concentrations in native, regrown and segmented hairs of cattle and pigs after repeated ACTH administrations

Adrenocorticotropic hormone (ACTH) is part of the hypothalamic-pituitary-adrenal axis response to stress and induces the release of cortisol, which is commonly used as an indicator in stress and animal welfare research. In recent years, hair cortisol concentration (HCC) gained increasing importance as a promising retrospective indicator for stress in animals. Thus, the aim of our study was to validate HCC as a potential indicator of increased endogenous cortisol release in cattle and pigs by repeated ACTH administrations followed by cortisol analysis in different hair types. For this purpose, 34 cattle and 38 gilts were treated either with repeated i.m. injections of ACTH or saline every second day over a period of 4 weeks. Saliva samples were taken before and after injections once a week from selected animals to verify the endogenous cortisol response. At the end of the treatment (week 4) and after 8 and 12 weeks, samples of natural and regrown hair were taken from the caudo-dorsal region of the back and analyzed for cortisol concentrations. In addition, natural hair was sampled after 12 weeks and cut into segments prior to analysis. Treatment with ACTH revealed a significant increase in salivary cortisol after application in both species, although this increase was attenuated in pigs compared to cattle. In week 4, HCCs were significantly elevated in natural and regrown hair of ACTH-treated animals. In cattle, HCCs significantly increased after ACTH treatment in natural, regrown and segmental hair compared with control animals, indicating that HCC may be a promising indicator of stress, as cortisol levels in all hair types reflected the preceding period with increased cortisol release. In pigs, there were no differences in HCCs between treatments. This may be caused by the lower systemic cortisol response in pigs, but seasonally reduced hair growth and external cross-contamination of hair by saliva and urine under commercial husbandry conditions may also interfere with the validity of HCC in this species.

Hair cortisol as a reliable indicator of stress physiology in the snowshoe hare: Influence of body region, sex, season, and predator-prey population dynamics

Hair cortisol concentration is increasingly used as a convenient, non-invasive, and integrative measure of physiology and health in natural populations of mammals. However, the use of this index is potentially confounded by individual variation in body region-specific differences in cortisol deposition rates. Here we examine correlations in cortisol concentrations in hair collected from the ear, shoulder, and thigh of wild snowshoe hares, Lepus americanus, as well as the influence of sex on cortisol measurements. We further evaluated this technique's ability to capture seasonal and cyclical patterns of snowshoe hare glucocorticoid secretion from 2013 to 2015 in the southwestern Yukon (Canada). We found positive correlations (R² = 0.20-0.32) in all pairwise comparisons among body regions, and differences among individuals accounted for the greatest proportion of variance (47.3%) in measurements. From 2013 to 2015 the hares' primary predator - Canada lynx - approximately doubled in population abundance. We found a significant increase in hare hair cortisol concentrations across this time period. Cortisol indices were higher in summer than winter pelage, reflecting predicted physiological responses to seasonal variation in food availability and individual risk. Variation in hair cortisol concentrations was more similar to long-term (weeks-months) integrative indices of adrenal capacity than point samples of fecal glucocorticoid metabolite concentrations. Overall, we find that hair cortisol analysis is a simple and useful tool for estimations of population-level stress physiology in wild mammals, and sampling of core body regions with consistent moulting patterns produced the most robust results in this species.

Temporary Relocation during Rest Periods: Relocation Stress and Other Factors Influence Hair Cortisol Concentrations in Horses

Horse transportation for temporary relocation during rest periods is a common and widespread practice among horse owners, either from sport competition or working tasks. This study aimed to determine the effect of a relocation period and the multiple factors associated with a rest period on hair cortisol concentrations (HCCs) in horses. Additionally, this study reports the seasonal effect on HCCs and hair growth over a year. Thirteen police horses, Pure Spanish stallions of various ages (5-13 y), were selected to participate in this study. Hair sample collection was carried out approximately every 30 d for seven months (Study 1) and a year (Study 2). Cortisol determinations were performed by enzyme immunoassay. Interestingly, Study 1 revealed that relocated horses (n = 4) exhibited elevated HCCs compared with control horses (n = 4) after the relocation period (p < 0.05). Study 2 (n = 5) showed higher HCCs during summer compared with autumn and winter, and higher hair growth rates in winter compared with the other seasons (p < 0.05). Relocated horses had higher HCCs, suggesting a change in their welfare status, probably related to the sudden change in their surrounding conditions. However, these results should be interpreted cautiously due to the low sample size used. The nature of the relationship between HCCs and horse welfare needs to be further examined.

Hair cortisol analyses in different mammal species: choosing the wrong assay may lead to erroneous results

Wild animals are faced with a broad range of environmental stressors and research is needed to better understand their effect on populations. Hormone analysis based on enzyme immunoassays (EIAs) can provide valuable information on adrenocortical activity (stress), and assessment of cortisol in hair may allow the quantification of cortisol production. To validate hair hormone analysis, we compared two EIAs based on antibodies against cortisol-3-CMO-BSA and cortisol-21-HS-BSA for hair glucocorticoid (hGC) measurements in Egyptian mongoose, Iberian lynx, Alpine marmot, Asiatic black bear, spotted hyena and cheetah, with results obtained by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) measurements. Both EIAs were also characterized by HPLC immunograms. Our results revealed that the cortisol-21-HS EIA measured 2.3- to 12-fold higher hGC concentrations than the cortisol-3-CMO assay. In dependence of the species, high-performance liquid chromatography (HPLC) immunograms showed that up to 70% of immunoreactivities determined by the cortisol-21-HS constituted of unknown unpolar compounds leading to an overestimation of hGC. The cortisol-3-CMO EIA expressed a better specificity, with 32.1-67.4% of immunoreactivity represented by cortisol and cortisone. The LC-MS/MS analyses (gold standard) revealed that the cortisol-3-CMO EIA also resulted in an (up to 3-fold) overestimation of hGC, but EIA results were correlated with LC-MS/MS in the mongoose, the lynx, the spotted hyena and the marmot. No correlation was obtained for Asiatic black bears. As a result of our study, we strongly recommend to test any cortisol EIA for its specificity towards extracted hair components. In all analyzed species, except the Asiatic black bear, cortisone and cortisol were simultaneously present in hair extracts; consequently, an appropriate EIA should cross-react to these two glucocorticoid hormones and express negligible affinity towards substances with less polarity than corticosterone. Choosing the wrong EIA for hGC analyses may lead to overestimations of hGC or-in the worst case-to results that do not mirror real adrenocortical activity.

Large-scale spatial variation of chronic stress signals in moose

The physiological effects of short-term stress responses typically lead to increased individual survival as it prepares the body for fight or flight through catabolic reactions in the body. These physiological effects trade off against growth, immunocompetence, reproduction, and even long-term survival. Chronic stress may thus reduce individual and population performance, with direct implications for the management and conservation of wildlife populations. Yet, relatively little is known about how chronic stress levels vary across wild populations and factors contributing to increased chronic stress levels. One method to measure long-term stress in mammals is to quantify slowly incorporated stress hormone (cortisol) in hair, which most likely reflect a long-term average of the stress responses. In this study, we sampled 237 harvested moose Alces alces across Sweden to determine the relative effect of landscape variables and disturbances on moose hair cortisol levels. We used linear model combinations and Akaike’s Information Criterion (corrected for small sample sizes), and included variables related to human disturbance, ungulate competition, large carnivore density, and ambient temperature to estimate the covariates that best explained the variance in stress levels in moose. The most important variables explaining the variation in hair cortisol levels in moose were the long-term average temperature sum in the area moose lived and the distance to occupied wolf territory; higher hair cortisol levels were detected where temperatures were higher and closer to occupied wolf territories, respectively.

A sensitive chemiluminescence based immunoassay for the detection of cortisol and cortisone as stress biomarkers

An electrochemically based antibody immobilization was used to perform environmentally and clinically relevant immunoassays for stress hormones biomarkers (cortisol and cortisone) using chemiluminescence (CL) detection. To achieve CL detection, the ferrocene tag on the antibodies was first oxidised, and this then acted as a catalyst for the luminol and hydrogen peroxide CL reaction. The conditions were optimised and measurements were made with an incubation time of 30 min. Using this approach limits of detection were obtained of 0.47 pg ml−1and 0.34 pg ml−1alsoR20.9912 and 0.9902 for cortisol and cortisone respectively with a linear concentration from 0 to 50 ng ml−1. The method was then applied to Zebrafish whole body and artificial saliva samples. For the Zebrafish sample recoveries of 91.0% and 90.0% were obtained with samples spiked with cortisol and cortisone, for artificial saliva the recoveries were 92.59% and 90.73% respectively. Interference studies showed only minor effects on the measurement of the analyte. A comparison between this procedure and the standard enzyme-linked immunosorbent assay (ELISA) procedure gave approximately the sameR2values.

Measuring Faecal Glucocorticoid Metabolites to Assess Adrenocortical Activity in Reindeer

Several non-invasive methods for assessing stress responses have been developed and validated for many animal species. Due to species-specific differences in metabolism and excretion of stress hormones, methods should be validated for each species. The aim of this study was to conduct a physiological validation of an 11-oxoaetiocholanolone enzyme immunoassay (EIA) for measuring faecal cortisol metabolites (FCMs) in male reindeer by administration of adrenocorticotrophic hormone (ACTH; intramuscular, 0.25 mg per animal). A total of 317 samples were collected from eight male reindeer over a 44 h period at Tverrvatnet in Norway in mid-winter. In addition, 114 samples were collected from a group of reindeer during normal handling and calf marking at Stjernevatn in Norway. Following ACTH injection, FCM levels (median and range) were 568 (268-2415) ng/g after two hours, 2718 (414-8550) ng/g after seven hours and 918 (500-6931) ng/g after 24 h. Levels were significantly higher from seven hours onwards compared to earlier hours (p < 0.001). The FCM levels at Stjernevatn were significantly (p < 0.001) different before (samples collected zero to two hours; median: 479 ng/g) and after calf marking (eight to ten hours; median: 1469 ng/g). Identification of the faecal samples belonging to individual animals was conducted using DNA analysis across time. This study reports a successful validation of a non-invasive technique for measuring stress in reindeer, which can be applied in future studies in the fields of biology, ethology, ecology, animal conservation and welfare.

Temporal profiles of cortisol accumulation and clearance support scale cortisol content as an indicator of chronic stress in fish

The development of chronic stress indicators for fish is of great interest, but appropriate non-invasive methods are lagging those used in terrestrial vertebrates. Here, we explore the possibility that levels of the stress hormone cortisol in scales could be used as a chronic stress indicator. Three experiments were conducted to assess the temporal profiles of cortisol rise and fall in plasma and scales of goldfish (Carassius auratus) in response to stressors of varying intensity and duration. Results show that a single acute air emersion stressor does not influence scale cortisol content. In contrast, relative to plasma levels, the fall in scale cortisol content following a high-dose cortisol implant is delayed by at least 8 days, and the rise and fall in scale cortisol content in response to unpredictable chronic stress are delayed by at least 7 days. Also, scale cortisol content is spatially heterogeneous across the body surface of goldfish. Overall, since high and sustained circulating cortisol levels are needed to influence scale cortisol content and the rates of cortisol accumulation and clearance are much slower in scales than in plasma, our results show that scales can provide an integrated measure of cortisol production and serve as a chronic stress indicator.

Faecal metabolites and hair cortisol as biological markers of HPA-axis activity in the Rocky mountain goat

Monitoring glucocorticoids in faeces and hair is increasingly used in ecological studies and provides a powerful and minimally intrusive mean to identify physiological challenges faced by wild animals. Using a cortisol and a corticosterone immunoassays, we conducted an adrenocorticotropic (ACTH) challenge with five weekly repeated injections to validate the use of faecal glucocorticoid metabolites and hair cortisol concentration as biological markers of the HPA-axis activity in captive mountain goats (Oreamnos americanus). We also investigated the effect of endogenous (age, sex, reproductive status) and methodological (faecal sample collection date, freezing delay and hair type) variables on cortisol values using faecal and hair samples collected from marked wild mountain goats during a long-term study. The cortisol enzyme immunoassay was reliable for mountain goat faeces and hair, and was sensitive enough to detect a clear rise in glucocorticoid concentration following ACTH injections for both matrices. Age and sex had no detectable effect on faecal glucocorticoid metabolites, but hair cortisol concentration was higher in kids and yearlings than in older goats, and lower in adult males compared to adult females. Reproductive status had no detectable effect on both faecal and hair measurements. Faecal metabolite concentrations increased with sample collection date in late spring until mid-summer and decreased afterward until early fall. Guard hair had nearly twice as much cortisol per gram as undercoat hair. Prolonged delay to freezing reduced the concentration of faecal glucocorticoid metabolites, but degradation seemed limited when samples were exposed to wind and sun or when ambient temperature was low. We conclude that faeces and hair can be used as valid biomarkers of the HPA-axis activity in mountain goat provided that confounding variables are taken into account when interpreting measurements.

A systematic review of studies utilizing hair glucocorticoids as a measure of stress suggests the marker is more appropriate for quantifying short-term stressors

Quantitating glucocorticoids (GCs) in hairs is a popular method for assessing chronic stress in studies of humans and animals alike. The cause-and-effect relationship between stress and elevated GC levels in hairs, sampled weeks later, is however hard to prove. This systematic review evaluated the evidence supporting hair glucocorticoids (hGCs) as a biomarker of stress. Only a relatively small number of controlled studies employing hGC analyses have been published, and the quality of the evidence is compromised by unchecked sources of bias. Subjects exposed to stress mostly demonstrate elevated levels of hGCs, and these concentrations correlate significantly with GC concentrations in serum, saliva and feces. This supports hGCs as a biomarker of stress, but the dataset provided no evidence that hGCs are a marker of stress outside of the immediate past. Only in cases where the stressor persisted at the time of hair sampling could a clear link between stress and hGCs be established.

Age, sex and storage time influence hair cortisol levels in a wild mammal population

The measurement of hair cortisol is increasingly used to understand the effect of natural and anthropogenic stressors on wild animals, but it is potentially confounded by individual, seasonal and sex-dependant variations in baseline cortisol secretion. This study validated an enzyme-linked immunoassay for hair cortisol measurement and characterized its baseline variation in a wild population of Egyptian mongoose. The analysis encompassed individuals of both sexes and all ages, across a range of geographic, environmental and seasonal conditions that the species experiences in Portugal allowing us to account for spatial, temporal and biological factors that contribute to hair cortisol variation. Our results showed that age, sex and storage time had an effect on hair cortisol, but season did not. Hair cortisol was higher in early stage juveniles compared to other age cohorts, in males when compared to females, and decreased with longer storage time. By identifying the factors that influence baseline hair cortisol in this wild population, we establish the basis for its application as an indicator of the effect of natural and anthropogenic stressors.

Variation in scale cortisol concentrations of a wild freshwater fish: Habitat quality or seasonal influences?

A significant body of literature suggests that aquatic pollutants can interfere with the physiological function of the fish hypothalamic-pituitary-interrenal (HPI) axis, and eventually impair the ability to cope with subsequent stressors. For this reason, development of accurate techniques to assess fish stress responses have become of growing interest. Fish scales have been recently recognized as a biomaterial that accumulates cortisol, hence it can be potentially used to assess chronic stress in laboratory conditions. We, therefore, aimed to evaluate the applicability of this novel method for cortisol assessment in fish within their natural environment. Catalan chub (Squalius laietanus) were sampled from two sites; a highly polluted and a less polluted (reference) site, in order to examine if habitat quality could potentially influence the cortisol deposition in scales. We also evaluated the seasonal variation in scale cortisol levels by sampling fish at three different time points during spring-summer 2014. In each sampling, blood was collected to complement the information provided by the scales. Our results demonstrated that blood and scale cortisol levels from individuals inhabiting the reference site were significantly correlated, therefore increasing the applicability of the method as a sensitive-individual measure of fish HPI axis activity, at least in non-polluted habitats. Since different environmental conditions could potentially alter the usefulness of the technique, results highlight that further validation is required to better interpret hormone fluctuations in fish scales. Scale cortisol concentrations were unaffected by habitat quality although fish from the polluted environment presented lower circulating cortisol levels. We detected a seasonal increase in scale cortisol values concurring with an energetically costly period for the species, supporting the idea that the analysis of cortisol in scales reveals changes in the HPI axis activity. Taken together, the present study suggests that cortisol levels in scales are more likely to be influenced by mid-term, intense energetically demanding periods rather than by long-term stressors. Measurement of cortisol in fish scales can open the possibility to study novel spatio-temporal contexts of interest, yet further research is required to better understand its biological relevance.

Investigation of the utility of feces and hair as non-invasive measures of glucocorticoids in wild black-tailed prairie dogs (Cynomys ludovicianus)

Non-invasive measures of glucocorticoid (GC) hormones and their metabolites, particularly in feces and hair, are gaining popularity as wildlife management tools, but species-specific validations of these tools remain rare. We report the results of a validation on black-tailed prairie dogs (Cynomys ludovicianus), a highly social engineer of the grasslands ecosystem that has experienced recent population declines. We captured adult female prairie dogs and brought them into temporary captivity to conduct an adrenocorticotropic hormone (ACTH) stimulation test, assessing the relationship between plasma GC and fecal glucocorticoid metabolite (FGM) levels following a single injection of a low (4 IU/kg) or high dose (12 IU/kg) of ACTH, compared to a single injection of saline. We also gave repeated injections of ACTH to adult females to assess whether this would result in an increase of hair cortisol concentrations, compared with control individuals repeatedly injected with saline. A single injection of ACTH at either low or high dose peaked plasma cortisol levels after 30 min, and thereafter the cortisol levels declined until 120 min, where they returned to pre-treatment levels comparable to those of the saline injected group. Despite the significant elevation of plasma cortisol in the treatment groups following ACTH injection, the elevation of FGM levels in the treatment groups were not significantly different from those in the control group over the following 12 h. Repeated injection of a high dose of ACTH failed to increase hair cortisol concentration in treatment animals. Instead, hair cortisol levels remained comparable to the pre-treatment mean, despite an increase in post-treatment hair cortisol levels seen in the saline-injected group. The magnitude of increase in the saline control group was comparable to natural seasonal variation seen in unmanipulated individuals. These results highlight that while measurement of GCs and their metabolites in feces and hair are potentially valuable conservation tools for black-tailed prairie dogs, further validation work is required before these matrices can be to real-world conservation applications.

Social stability influences the association between adrenal responsiveness and hair cortisol concentrations in rhesus macaques

Hair cortisol concentrations are increasingly being used in both humans and nonhuman animals as a biomarker of chronic stress. However, many details regarding how hair cortisol concentrations relate to the dynamic activity and regulation of the HPA axis are still unknown. The current study explores 1) how the regulation of the HPA axis in infancy relates to hair cortisol concentrations (HCC) in infancy 2) whether this relationship persists into adulthood under conditions of social stability, and 3) how social instability impacts these relationships. All subjects were rhesus monkeys housed in large social groups at the California National Primate Research Center, and all had participated in a 25-hr. long BioBehavioral Assessment (BBA) at 3-4 months of age when four plasma samples were taken to assess HPA regulation, in particular cortisol responses to 1) 2-hour social separation and relocation, 2) sustained challenge, 3) dexamethasone and 4) ACTH administration. In Study 1, hair samples were collected at the end of the BBA testing from 25 infant rhesus monkeys from 2 different stable social groups. In Study 2, hair samples were obtained at three timepoints from 108 adults from 3 different stable social groups (1 in the Spring/Summer and 2 in the Fall/Winter) to examine the temporal stability of the relationship between HCC and HPA axis regulation. In Study 3, subjects included 31 infants and 33 adults from a single social group experiencing social instability following the same procedures as in Studies 1 and 2. Generalized linear models were used to determine if infants' HPA axis activity and regulation predicted HCC in infancy (Study 1), in adulthood with animals living in stable social conditions (Study 2) or in animals living in an unstable social group (Study 3). Results indicated that for both infants and adults living in stable social groups, HCC are associated with the adrenal response to ACTH in infancy. Samples collected in the winter also had higher HCC than those collected in summer. In the unstable social group, adult hair cortisol levels were higher than in the stable social groups. Additionally, there were no consistent relationships between HCC and infant HPA axis regulation among adults or infants living in a group experiencing social instability. These results suggest that the aspects of the HPA axis that drive HCC may differ depending on context. Under stable, non-stressed conditions there seems to be a trait-like association between adrenal responsivity and HCC in infancy and adulthood. However, this association may be reduced or eliminated under conditions of social stress.

HEALTH SURVEY OF BOREAL CARIBOU (RANGIFER TARANDUS CARIBOU) IN NORTHEASTERN BRITISH COLUMBIA, CANADA

Boreal woodland caribou (Rangifer tarandus caribou) are listed as threatened across Canada, and a basic understanding of their health status is lacking. From December 2012 to April 2013, we investigated multiple health indices for adult female boreal caribou (n=163) captured from seven herds in NE British Columbia, Canada. Health indices included physical characteristics, physiologic and trace mineral status, exposure to or infection with selected pathogens, and measures of chronic stress and inflammation, including serum amyloid A, haptoglobin, and hair cortisol concentration. Key findings were exposure to the bacterium Erysipelothrix rhusiopathiae in 14% of individuals, mild to severe hair loss associated with winter tick (Dermacentor albipictus) infestations in 76% of caribou from December to early February and 81% from late February to early April, and evidence of trace mineral deficiencies with 99% and 34% of individuals deficient in copper and selenium, respectively. Seroprevalence for exposure to selected pathogens was: alphaherpesvirus (63%), pestivirus (1%), Besnoitia spp. (60%), and Neospora caninum (2%). All animals were seronegative to Brucella spp. and Toxoplasma gondii. Mycobacterium avium ssp. paratuberculosis was not detected in any fecal samples. Parasite eggs or larvae, including Parelaphostrongylus andersoni (36%), Skrjabinema spp. (1%), Strongyle-type eggs (11%), Moniezia-type eggs (8%), and nematodirines (3%), were detected on fecal examination, but at low intensity. Blood biochemistry values and hair cortisol concentrations were within ranges previously reported in Rangifer tarandus sspp. Some significant differences among herds were noted, including antler morphology, exposure to Besnoitia spp., and concentrations of serum amyloid A, copper, cobalt, manganese, and iron.

The use of hair cortisol for the assessment of stress in animals

The hair cortisol concentration (HCC) is assumed to be a retrospective marker of integrated cortisol secretion and stress over longer periods of time. Its quantification is increasingly used in psychoneuroendocrinological studies in humans, but also in animal stress and welfare research. The measurement of HCCs for the assessment of stress offers many considerable benefits for use in domesticated and wild animals, especially due to the easy and minimally invasive sampling procedure and the representation of longer time periods in one sample. This review aims to outline the different fields of application and to assess the applicability and validity of HCC as an indicator for chronic stress or long-term activity of the hypothalamic-pituitary-adrenal axis in wild and domesticated animals. Specific hair characteristics are presented and the advantages and limitations of using HCC are discussed. An overview of findings on the impact of stress- and health-related factors on HCCs and of diverse influencing factors causing variation in hair cortisol levels in different species is given. Recommendations for the use of hair cortisol analysis are proposed and potential fields of future research are pointed out. The studies indicate an effect of age and pregnancy on HCCs, and cortisol incorporation into hair was also found to depend on hair colour, body region, sex and season of year, but these results are less consistent. Furthermore, the results in animals show that a wide array of stressors and pathological conditions alters the cortisol concentrations in hair and that HCC thereby provides a reliable and valid reflection of long-term cortisol secretion in many species. However, more research is necessary to investigate the underlying mechanisms of cortisol incorporation into the hair and to explore the hair growth characteristics in the species of interest. To overcome confounding influences, the use of standardized sampling protocols is strongly advised.