Use of salivary cortisol to evaluate the influence of rides in dromedary camels

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.

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.

How individual, social, and ecological conditions influence dispersal decisions in male vervet monkeys

Dispersal between social groups reduces the risk of inbreeding and can improve individuals' reproductive opportunities. However, this movement has costs, such as increased risk of predation and starvation, loss of allies and kin support, and increased aggression associated with entering the new group. Dispersal strategies, such as the timing of movement and decisions on whether to transfer alone or in parallel with a peer, involve different costs and benefits. We used demographic, behavioral, hormonal, and ecological data to examine the causes and consequences of 36 dispersal events from 29 male vervet monkeys (Chlorocebus pygerythrus) at Lake Nabugabo, Uganda. Adult males' secondary dispersal coincided with the conception season in females, and males improved their potential access to females by moving to groups with higher female-to-male sex ratios and/or by increasing their dominance rank. Males that dispersed with a peer had lower fecal glucocorticoid and androgen metabolite levels than lone dispersers. Subadult males were not more likely to engage in parallel dispersals compared to adult males. Dispersal was also used as a mechanism to avoid inbreeding, but changes in hormone levels did not seem to be a trigger of dispersal in our population. Our findings illustrate the complex individual strategies used during dispersal, how many factors can influence movement decisions, as well as the value of dominance and hormone analyses for understanding these strategies.

Temporal stability of fecal cortisol metabolites in mountain-dwelling ungulates

Fecal cortisol metabolites (FCMs) are widely used to track stress responses in wildlife and captive species. Rules of thumb suggest that samples should be collected as soon as possible after defecation, to avoid decay of FCMs. To date, however, only a few studies investigated the stability of defecated FCMs over time, and most of them were conducted in controlled laboratory conditions. Here, we investigated the stability of FCMs over seven consecutive days, in two mountain-dwelling ungulates, under natural environmental conditions using a semi-experimental approach. Fecal samples from Northern chamois Rupicapra rupicapra (n = 24) and red deer Cervus elaphus (n = 22) were collected in summer of 2020 within the Stelvio National Park, Italy, and placed in an open area above 2000 m a.s.l. For the next 7 days, we collected a portion of each sample, and all sub-samples were analyzed with an 11-oxoetiocholanolone enzyme immunoassay. Exposure, temperature, and precipitation were fitted as covariates in non-linear generalized mixed models to assess FCM variation over time, and competing models were selected using AICc. For chamois, the best model included only time as a predictor, while for red deer, it included time, precipitation, and exposure. For both species, FCM values decreased rapidly from the first days after deposition until the fourth day. For red deer, in northern-exposed samples, FCM values decreased slower than in south-exposed ones; furthermore, FCM values increased with increasing precipitation. Our results offer a solid methodological basis to wildlife researchers and practitioners interested in the investigation of the ecological factors affecting stress variation in wildlife and support the recommendation to collect samples as fresh as possible, to avoid misleading inference. Further studies are necessary to evaluate the stability of FCMs when other enzyme immunoassays are used.

Hormonal correlates of male dominance rank, age, and genital colouration in vervet monkey (Chlorocebus pygerythrus)

Primates are the most colourful members of the Mammalian clade. In vervet monkeys (Chlorocebus pygerythrus), males are characterized by their red penis and blue scrotum. Such colour signals are often used in conspecific communication, and thus could be used to convey signaller condition. We quantified scrotal and penile colour characteristics using digital photographs between May-June 2016 from males in two neighboring groups along the shores of Lake Nabugabo, Uganda. We examined the relationship between fecal hormones, male dominance rank, age (adult vs. immature), and colour. Adult males were higher ranking than immatures, but there were no rank or age differences in fecal hormone levels. Glucocorticoids and androgens were positively correlated in immature, but not adult males. All scrotal characteristics were predicted by age, with adult males having more teal (i.e., less blue, more green) and more luminant scrota. Within adult males, those with higher androgens levels had more saturated blue scrotal colouration and higher-ranking males were more luminant. Penile colouration was also associated with age and rank. High-ranking males had a more saturated red penis, and adult male penile colour was more luminant and bluer than in immature males. Our findings are consistent with previous reports that scrotal colouration advertises sexual or reproductive maturity (i.e., age), but we also find that within adult males, colour also advertises dominance rank and may be mediated by androgen levels. Penile colouration also appears to signal information about male age and dominance rank but does not appear to be mediated by hormones.

Effects of Positive Reinforcement Training and Novel Object Exposure on Salivary Cortisol Levels under Consideration of Individual Variation in Captive African Elephants (Loxodonta africana)

Simple Summary

Regular training for medical or enrichment purposes and the provision of environmental enrichment, such as varied feeding schedules and novel objects, are part of the management of African elephants in zoos. The present study aimed to find out whether training and enrichment in the form of a novel object induced physiological changes in captive African elephants. We repeatedly sampled the saliva of ten animals (three zoos) before and after training and the exposure to a novel object for the analysis of cortisol and as a measure of stress and arousal. We found high salivary cortisol levels before and low levels after training. A novel object, in contrast, moderately increased the salivary cortisol levels. Moreover, males and young elephants showed lower salivary cortisol levels than females and old elephants, respectively. The zoo, handling method (free vs. protected contact to keepers), reproductive and social status, however, did not influence the salivary cortisol levels of the animals studied. We conclude that the relatively high cortisol values before training could be due to anticipation of the training event. A novel object, in contrast, may have evoked arousal, which led to the observed cortisol increase. In addition, understanding why animals differ in stress responses will help to manage stress in zoo elephants with the goal of ensuring their welfare.

Abstract

Dealing with potential stress in species that have high husbandry requirements, such as elephants, is a challenge for zoos. The objective of the present study was to determine whether positive reinforcement training (PRT) and exposure to a novel object (NOV) for enrichment induced a salivary cortisol response indicative of activation of the hypothalamic–pituitary–adrenal (HPA) axis and which factors determine individual variation in this regard in captive African elephants. We repeatedly sampled the saliva of ten animals (three zoos) for the analysis of cortisol (SACort) before and up to 60 min (in 10–15 min intervals) after the onset of PRT (three repeats) or NOV (nine repeats), which lasted 10 min. There was considerable individual variation in SACort in response to PRT or NOV. Using mixed models, we were able to control these and to reveal that PRT was associated with high SACort before and relatively low SACort after PRT, while NOV induced a moderate SACort increase. The individual differences in SACort were related to age and sex (NOV), while the effects of zoo, handling method (free vs. protected contact) and reproductive and social status were variable. We conclude that positive affective states, such as anticipation or arousal, should be taken into account when interpreting the differences in the SACort responses between PRT and NOV. In addition, understanding the individuality of stress will support management decisions aimed at promoting captive elephant welfare.

Does Experience Make Hucul Horses More Resistant to Stress? A Pilot Study

The aim of the study was to determine whether experience related to horse age and number of starts in championships influences stress level, measured by salivary cortisol concentration. The study involved 18 clinically healthy Hucul mares who participated in the Polish Championships for Hucul Horses. Evaluation of performance value was carried out in accordance with the guidelines specified in the breeding and genetic resources conservation program for this breed. The championship lasted two days, consisting of conformation evaluation, endurance, and Hucul path. Saliva was collected at baseline (T1), after arena assessment (T2), after endurance (T3), and on the second day after the Hucul path (T4). Cortisol levels increased from an average of 2.73 ± 1.18 ng/mL (T1) to 10.46 ± 8.03 ng/mL after T3. Significantly lower levels of free cortisol were detected in the saliva of the younger mares, up to 9 years old, and mares who participated in only one qualifying path after each element of the championship. The highest levels of cortisol (T3) were found in mares competing repeatedly on the qualifying path. No correlation was found between cortisol levels and the championship results. Participation of mares in the championship was associated with stress, which was reflected in the increase in cortisol levels in saliva.

Glucocorticoid Production, Activity Levels, And Personality Traits Of Fennec Foxes (Vulpes zerda) Managed For Different Roles In Zoos

Fecal glucocorticoid metabolite (FGM) concentrations, activity, and personality were assessed for 35 fennec foxes (Vulpes zerda) to determine whether animals managed as ambassadors differed from exhibit or off-exhibit animals. A FGM assay, pedometer, and personality assessment tool were validated. Then, fecal samples and movement data were collected during winter and summer periods. Handling was recorded, and the personality of each fox was evaluated. Generalized linear mixed models assessed the relationships between FGM concentrations, activity, personality, handling, sex, season, rearing type, and role. FGM concentrations did not differ in relation to role or handling. Foxes were most active at night; the time of peak activity did not vary with role or handling. Foxes were more active in winter; males were more active than females, and ambassador foxes were more active than off-exhibit animals. Hand-reared foxes were more sociable, and, at one institution, ambassador foxes were more sociable than foxes in other roles. These results suggest that management for ambassador programs is not associated with changes in glucocorticoid production or circadian patterns but may increase activity and be associated with greater sociability.

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.

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.

Conservation Education: Are Zoo Animals Effective Ambassadors and Is There Any Cost to Their Welfare?

Animal ambassador encounters (AAE), where visitors come into close-contact with animals, are popular in zoos and are advocated as promoting connection to wild species. However, educational and animal-welfare implications are relatively unknown. We conducted a systematic literature review (PRISMA) to investigate visitor and animal outcomes of AAE. We identified 19 peer reviewed articles and 13 other records focused on AAEs. Although we found net positive or neutral impacts overall, several studies indicated that high-intensity visitor contact and long-term exposure may be detrimental to animal welfare. Most studies lacked rigour and claims were based on an absence of negative impacts rather than evidence of benefits. Multiple publications were derived from the same datasets and there were no standardised measures for either welfare or education impacts. Of the peer-reviewed articles, just two considered both education and welfare. Education studies often used perceived learning or only post-experience testing. Welfare studies used small samples (median n = 4; range 1–59), and limited measures of welfare. In order to justify the continued use of AAEs in modern zoos, animal welfare costs must be proven to be minimal whilst having demonstrable and substantial visitor educational value. Large-scale, standardised impact assessments of both education and welfare impacts are needed.

Camel Genetic Resources Conservation through Tourism: A Key Sociocultural Approach of Camelback Leisure Riding

Camels are exotic elements, which can be comprised within adventure travel companies promoting ecotourism activities. Such recreations contribute to sustainable livelihoods for local communities and educational empowerment towards nature and its conservation. At present, some local camel breeds' survival reduces to this animal-based leisure industry and its reliability to perform and promote customized services accurately. By conducting an on-site questionnaire to customers participating in camelback riding tours, we assessed the motivational factors affecting participation, satisfaction, and loyalty in this tourism segment that may have made it socially differentiated. The sixfold combination of staff performance, culture geography, diverse and humane close interaction, camel behavior and performance, sociotemporal context, and positive previous experience involves the elemental dimensions that explain customer satisfaction and return intention probability within this entertainment business. Customer knowledge is essential for stakeholders to build personalized riding experiences and align profits with environmental sustainability and biodiversity mainstream concerns into their everyday operations. In turn, domestic camel tourist rides could be managed as a viable path to nature conservation by helping endangered local breeds to avoid their functional devaluation and potential extinction.

Physical and Physiological Indicators of Welfare in Guinea Pigs (Cavia porcellus) Serving as Ambassador Animals

Special encounters that allow contact between animals and guests are common in zoos and aquariums. Visitors to the Saint Louis Zoo may touch guinea pigs serving as ambassador animals. We evaluated two welfare indicators in ambassador guinea pigs by comparing glucocorticoid levels and body weights between periods when guinea pigs lived in a habitat accessible to the public and while off exhibit. Mean glucocorticoid levels did not differ between sexes or between on- and off-exhibit periods. There was significant individual variation, and females demonstrated greater variation than males. While on exhibit, glucocorticoid levels slightly but significantly increased in males and decreased in females. Moving guinea pigs between habitats only elicited a significant glucocorticoid response when females were moved off exhibit. Temporary closures of the exhibit had no effect on glucocorticoid levels in either sex. Analyses of the impact of handling rates on males found no impact on glucocorticoid levels. Guinea pigs' body weights were lower while on exhibit. We conclude that guinea pigs serving as ambassador animals at the Saint Louis Zoo demonstrate comparable physiological profiles while on and off exhibit and, when used in a rotational schedule, are a suitable species for animal encounters involving contact with the public.

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.

The effects of body region, season and external arsenic application on hair cortisol concentration

Hair cortisol analysis has been used to quantify hormone levels in circulation in several mammal species. Hair remains stable for decades or centuries, allowing researchers to use archived hair samples to investigate hormone levels that span long time periods. However, several studies have found that intra-individual variability, driven by the body region from which a sample is derived, confounds measurements of systemic glucocorticoid hormone concentrations. In addition, the external application of chemical agents to hair can remove or concentrate molecules of interest. These may preclude the use of samples that have been collected opportunistically and/or those that have been housed in museum collections. Using a captive population of Vancouver Island marmots (Marmota vancouverensis), we found a strong effect of body region on the concentration of cortisol within hair, as well as an effect of season. Using a collection of American mink (Neovison vison) pelts, we found that application of the preservative arsenic in the form of a soap does not cause a significant decrease in cortisol. The marmot results suggest that intra-individual variability is not stable through time. The reason for these seasonal effects is not clear and further study is necessary. Researchers using samples from an unknown body region should exercise caution in interpreting their results. The mink results suggest that samples held in museum collections can be used to quantify cortisol, even when arsenic preservation is suspected.

The 24/7 approach to promoting optimal welfare for captive wild animals

We have an ethical responsibility to provide captive animals with environments that allow them to experience good welfare. Husbandry activities are often scheduled for the convenience of care staff working within the constraints of the facility, rather than considering the biological and psychological requirements of the animals themselves. The animal welfare 24/7 across the lifespan concept provides a holistic framework to map features of the animal's life cycle, taking into account their natural history, in relation to variations in the captive environment, across day and night, weekdays, weekends, and seasons. In order for animals to have the opportunity to thrive, we argue the need to consider their lifetime experience, integrated into the environments we provide, and with their perspective in mind. Here, we propose a welfare assessment tool based upon 14 criteria, to allow care staff to determine if their animals' welfare needs are met. We conclude that animal habitat management will be enhanced with the use of integrated technologies that provide the animals with more opportunities to engineer their own environments, providing them with complexity, choice and control.

Parasites, stress and reindeer: infection with abomasal nematodes is not associated with elevated glucocorticoid levels in hair or faeces

Stress hormones (glucocorticoids), incorporated into hair/fur and faeces, have been proposed as biomarkers of overall health in wildlife. Although such biomarkers may be helpful for wildlife conservation and management, their use has rarely been validated. There is a paucity of studies examining the variation of stress hormones in mammals and how they relate to other health measures, such as parasitism. Parasites are ubiquitous in wildlife and can influence the fitness of individual animals and populations. Through a longitudinal experiment using captive reindeer (Rangifer tarandus tarandus), we tested whether animals infected with Ostertagia gruehneri, a gastrointestinal nematode with negative impacts on fitness of the host, had higher stress levels compared with those that had been treated to remove infection. Faecal samples were collected weekly for 12 weeks (June-September) and hair was collected at the start and end of the study; glucocorticoids were quantified using enzyme immunoassays. Contrary to what was expected, infected reindeer had similar levels of cortisol in hair and slightly lower glucocorticoid metabolites in faeces compared with uninfected reindeer. Faecal corticosterone levels were higher than faecal cortisol levels, and only corticosterone increased significantly after a handling event. These results suggest that reindeer may use a tolerance strategy to cope with gastrointestinal nematodes and raise the question as to whether moderate infection intensities with nematodes are beneficial to the host. By removing nematodes we may have altered the gut microbiota, leading to the observed elevated faecal glucocorticoid metabolite levels in the treated reindeer. These findings demonstrate the importance of considering both cortisol and corticosterone in physiological studies, as there is mounting evidence that they may have different functionalities.