Non-invasive assessment of adrenocortical function in the male African elephant (Loxodonta africana) and its relation to musth

Faecal 11-ketoetiocholanolone measurement in Iberian red deer (Cervus elaphus hispanicus): validation of methodology using HPLC–MS/MS

A cortisol metabolite, 11-ketoetiocholanolone (11-k), is widely used in monitoring stress in several vertebrates, and can be detected by immunoassay. However, these assays have certain limitations with respect to specificity. Also, differences in the excretion of faecal glucocorticoid metabolites (FGM) among species and even between sexes make validation necessary in each case. Therefore, our aims were, first, to develop and validate a high-pressure liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) methodology for monitoring 11-k in faeces of Iberian red deer (Cervus elaphus hispanicus), and second, to investigate the capability of our method to determine variations of this FGM in a longitudinal study. Third, and finally, we assessed the correspondence between faecal 11-k concentrations and plasma cortisol. An adrenocorticotropic hormone (ACTH) test was performed on six red deer stags translocated and kept in captivity for a week and faecal samples were collected twice a day. One single blood and faecal sample from another seven stags was also collected after 2 weeks in captivity. The results of the longitudinal study showed a first peak in 11-k 36 h after the ACTH test and handling, and a second peak at 120 h of being kept indoors. Maximum concentrations of 11-k ranged from 22.71 to 375.68 ng/g. In the second stag group, 11-k concentrations of 25.09 ± 20.53 ng/g had a correlation of r2 = 0.88 with the concentration of plasma cortisol, which was 54.6 ± 55.1 ng/mL. This technique is capable of detecting changes in the concentrations of faecal 11-k. The values determined have a good correlation with the cortisol concentration in blood, and we also detected differences in different individuals’ responses to the same stressors.

Androgen and androgen metabolite levels in serum and urine of East African chimpanzees (Pan troglodytes schweinfurthii): comparison of EIA and LC-MS analyses

The primary male androgen testosterone (T) is often used as an endocrinological marker to investigate androgen-behaviour interactions in males. In chimpanzees and bonobos, studies investigating the relationship between T levels and dominance rank or aggressive behaviour have revealed contradictory results. The immunoassays used in these studies were originally developed for the measurement of steroids in serum. Their application to non-invasively collected samples, however, can lead to methodological problems due to cross-reacting metabolites, which might occur in urine or faeces but not in blood. The overall aim of this study, therefore, is to clarify whether a T enzyme immunoassay (EIA) is an applicable method to monitor testicular function in adult male chimpanzees. To estimate the impact of cross-reacting androgens on the used T EIA, we compared the results of an EIA measurement with a set of androgen metabolite levels measured by LC-MS. In urine from male chimpanzees, cross-reactivities appear to exist mainly with T and its exclusive metabolites, 5α-dihydrotestosterone (5α-DHT) and 5α-androstanediol (androstanediol). Both urinary and serum T levels of male chimpanzees were significantly higher than female T levels when measured with the T EIA, indicating a reliable measurement of testicular androgens and their exclusive metabolites with the used EIA. In urine from female chimpanzees, the comparison between LC-MS and T EIA results indicated a higher impact of cross-reactions with adrenal androgen metabolites. Therefore, the investigation of urinary T levels in female chimpanzees with a T EIA seems to be problematic. Overall our results show that a T EIA can be a reliable method to monitor testicular function in male chimpanzee urine and that LC-MS is a valuable tool for the validation of immunoassays.

Simultaneous measurement of endogenous steroid hormones and their metabolites with LC-MS/MS in faeces of a New World primate species, Cebus capucinus

We developed and validated a method to measure steroid hormones with liquid chromatography-tandem mass spectrometry (LC-MS/MS) in faecal samples of white-faced capuchins. The method includes the measurement of adrenal and gonadal hormones such as cortisol, testosterone, estrone, progesterone and a number of their faecal metabolites. This method can be used for simultaneous routine measurements of steroids in faecal samples and provides a reference method for the validation of new immunoassays in this matrix. The optimised method consists of an extraction of the dried faecal samples with 80% methanol followed by purification of the extracts by solid phase extraction, solvolytic cleavage of conjugates and liquid-liquid extraction. Extracts were measured by LC-MS/MS with an electrospray interface in positive ionisation mode. Out of 19 steroids spiked into methanol extracts, 14 showed a recovery of 79.8-118.5% with an intra-day precision of 2.5-13.0% and an inter-day precision of 7.2-15.1%. Detection limits for these steroids ranged from 0.3 to 27.0 ng/mL of extract. Five steroids did not fulfil our requirements concerning precision and accuracy and we therefore considered these to not be reliably measurable with this method. While there was no indication of considerable amounts of conjugated forms for most metabolites, 87% of the testosterone was found in the solvolysis fraction, which indicates that the majority of testosterone was conjugated. Therefore, solvolysis turned out to be crucial, especially for the quantification of the total amount of testosterone. The physiological validation of this LC-MS/MS method confirmed known physiologically caused differences in faecal steroid concentrations. This indicates the usefulness of the method in investigating variation in the levels of major steroid hormones in faeces of white-faced capuchins. The possibility to simultaneously measure hormones of the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-pituitary-gonadal (HPG) axis makes this method suitable for dealing with questions concerning the cross talk between those axes.

Species-specific patterns in fecal glucocorticoid and androgen levels in zoo-living orangutans (Pongo spp.)

In contrast to most primate species, including the other great apes, orangutans maintain a fission-fusion social system in the wild without being part of a stable community. In zoos, however, they are kept in permanent groups, usually consisting of one adult male and several females. In zoo orangutans, we predict higher levels of glucocorticoids and androgens in the Bornean species compared to its congener from Sumatra, due to the much more solitary lifestyle of Bornean orangutans and the apparent higher frequency of male aggression directed towards females in this species in the wild. To compare hormone levels of the two orangutan species, we validated a fecal glucocorticoid and a fecal androgen assay. Subsequently, fecal samples from a total of 73 female and 38 male orangutans housed in 29 European zoos were analyzed to investigate the effect of species, social group size, age and (for female glucocorticoid levels) reproductive state and the presence of adult males on fecal hormone metabolite concentrations. The results of linear mixed effect models indicate that both male and female Bornean orangutans show a steeper increase in glucocorticoid levels with increasing group size than Sumatran orangutans. We therefore conclude that Sumatran zoo orangutans are better able to adjust to social housing conditions than their Bornean congeners. In addition, our analyses reveal higher glucocorticoid levels in lactating females of both species compared to non-lactating and juvenile females. Concerning androgen levels in males, our analyses revealed significantly higher concentrations in Bornean than Sumatran orangutans. These differences in both glucocorticoid and androgen output between the two species of orangutan are presumably linked to ecological and behavioral differences and could possibly be attributed to phenotypic plasticity. However, given that we found interspecific differences in hormone excretion in captivity, where both species live under very similar conditions, we conclude that this variation has a genetic basis.

Selection for fast and slow exploration affects baseline and stress-induced corticosterone excretion in Great tit nestlings, Parus major

In nestlings, glucocorticoid (GC) secretion has short-term and long-term fitness consequences. For example, short-time elevations trigger begging activity, whereas chronically elevated GC levels impair body condition, growth and cognitive abilities. Despite a growing body of literature on personality traits, the effects of selection for fast and slow exploration on GC secretion have received little attention. We compared baseline and stress-induced hypothalamic-pituitary-adrenal (HPA) axis activity of hand-reared great tit nestlings of lines selected for fast and slow exploration. Nestling droppings were collected under three conditions: control, test (following handling stress, day 14 after hatching) and the following day. The concentrations of excreted immunoreactive corticosterone metabolites (CM) were determined via an enzyme immunoassay. We also observed nestlings' begging behaviour. CM differed significantly between the lines. Nestlings of the fast line excreted lower CM than slow-line birds. In response to handling stress, nestlings excreted significantly higher concentrations of CM than during the control and on the day after handling. Sex and begging activity were not related to CM levels. Under the control condition, but not after handling, males begged significantly more often than females. In both lines, adults excreted significantly less CM compared to nestlings. Both nestlings and adults of the slow line produced higher baseline CM values than fast-line birds. Fast-line nestlings excreted lower baseline CM than nestlings of a wild population not selected for fast or slow exploration. Slow-line nestlings did not. Our results show that selection on the basis of exploratory behaviour affected HPA axis reactivity.

Measuring salivary analytes from free-ranging monkeys

Studies of large free-ranging mammals have been revolutionized by non-invasive methods for assessing physiology, which usually involve the measurement of fecal or urinary biomarkers. However, such techniques are limited by numerous factors. To expand the range of physiological variables measurable non-invasively from free-ranging primates, we developed techniques for sampling monkey saliva by offering monkeys ropes with oral swabs sewn on the ends. We evaluated different attractants for encouraging individuals to offer samples, and proportions of individuals in different age/sex categories willing to give samples. We tested the saliva samples we obtained in three commercially available assays: cortisol, salivary alpha amylase, and secretory immunoglobulin A. We show that habituated free-ranging rhesus macaques will give saliva samples voluntarily without training, with 100% of infants, and over 50% of adults willing to chew on collection devices. Our field methods are robust even for analytes that show poor recovery from cotton, and/or that have concentrations dependent on salivary flow rate. We validated the cortisol and SAA assays for use in rhesus macaques by showing aspects of analytical validation, such as that samples dilute linearly and in parallel to assay standards. We also found that values measured correlated with biologically meaningful characteristics of sampled individuals (age and dominance rank). The SIgA assay tested did not react to samples. Given the wide range of analytes measurable in saliva but not in feces or urine, our methods considerably improve our ability to study physiological aspects of the behavior and ecology of free-ranging primates, and are also potentially adaptable to other mammalian taxa.

Endocrine correlates of musth and the impact of ecological and social factors in free-ranging African elephants (Loxodonta africana)

Sexual activity in mature male African elephants is predominantly associated with the occurrence of musth, a state or condition which refers to a set of physical, physiological and behavioral characteristics, including an elevation in androgen levels. Although musth appears to be energetically costly, the degree to which it is associated with changes in adrenal endocrine function (e.g., glucocorticoid output) is still unclear. To investigate the possible effect of musth on adrenocortical function, and the impact of socioecological changes on androgen and glucocorticoid levels, six adult African elephant bulls were followed for 13months in the Kruger National Park, South Africa, and observations and fecal sample collection for endocrine monitoring was carried out about twice weekly. Our data showed that the occurrence of musth was associated with reduced glucocorticoid output, suggesting that musth does not represent a physiological stress mediated by the hypothalamic-pituitary-adrenal axis. This confirms previous findings in captive-housed animals, providing evidence for a suppressive effect of the musth condition on adrenocortical activity. Furthermore, a seasonal effect on androgen and glucocorticoid levels was found, which appears to vary depending on the reproductive status of the animal. The results also indicate a relationship between the presence or absence of social partners and changes in testicular and adrenal endocrine activity. Finally, the data confirm previous findings in captive-housed elephants, that an elevation in androgen concentrations usually occurs before the onset of physical musth signs, and therefore support the idea that the change in androgen levels represents the initial stimulus for the musth condition.

Simplified method to measure glucocorticoid metabolites in faeces of horses

Glucocorticoids or their metabolites can be measured in several body fluids or excreta, including plasma, saliva, urine and faeces. In recent years the measurement of glucocorticoid metabolites (GCMs) in faeces has gained increasing attention, because of its suitability for wild populations. In horses, however, the group-specific enzyme immunoassay described so far has a limited practicability due to its complex extraction procedure. Therefore, we tested the applicability of other enzyme immunoassays for glucocorticoid metabolites. The present study clearly proved that an enzyme immunoassay (EIA) for 11-oxoaetiocholanolone using 11-oxoaetiocholanolone-17-CMO: BSA (3alpha,11-oxo-A EIA) as antigen showed high amounts of immunoreactive substances. Therefore it was possible to use just a small amount of the supernatant of a methanolic suspension of faeces. The results correlated well with the already described method for measuring GCMs in horse faeces, i.e. analysing the samples with an EIA after a two step clean up procedure of the samples (Merl et al. 2000). In addition, the 3alpha,11-oxo-A EIA has the advantage of providing a bigger difference between baseline values and peak values after ACTH stimulation. The new assay increased the accuracy of the test, lowered the expenses per sample, and storing samples at room temperature after collection was less critical than with other assays investigated in our study. This is a big advantage both in the field of wildlife management of equids and in the field of equestrian sports and it shows the importance of choosing an assay which is in good accordance with the metabolites excreted in a given species.

A safer method for studying hormone metabolism in an Asian elephant (Elephas maximus): accelerator mass spectrometry

Noninvasive hormone assays provide a way to determine an animal's health or reproductive status without the need for physical or chemical restraint, both of which create unnecessary stress for the animal, and can potentially alter the hormones being measured. Because hormone metabolism is highly species-specific, each assay must be validated for use in the species of interest. Validation of noninvasive steroid hormone assays has traditionally required the administration of relatively high doses of radiolabelled compounds (100 µCi or more of (14)C labeled hormone) to permit subsequent detection of the excreted metabolites in the urine and feces. Accelerator mass spectrometry (AMS) is sensitive to extremely low levels of rare isotopes such as (14)C, and provides a way to validate hormone assays using much lower levels of radioactivity than those traditionally employed. A captive Asian bull elephant was given 1 µCi of (14)C-testosterone intravenously, and an opportunistic urine sample was collected 2 hr after the injection. The sample was separated by HPLC and the (14)C in the fractions was detected by AMS to characterize the metabolites present in the urine. A previously established HPLC protocol was used, which permitted the identification of fractions into which testosterone sulfate, testosterone glucuronide, and the parent compound testosterone elute. Results from this study indicate that the majority of testosterone excreted in the urine of the Asian bull elephant is in the form of testosterone sulfate. A small amount of testosterone glucuronide is also excreted, but there is no parent compound present in the urine at all. These results underscore the need for enzymatic hydrolysis to prepare urine samples for hormone assay measurement. Furthermore, they highlight the importance of proper hormone assay validation in order to ensure accurate measurement of the desired hormone. Although this study demonstrated the utility of AMS for safer validation of noninvasive hormone assays in nondomestic species, this methodology could also be applied to studies of nutrient metabolism and drug pharmakokinetics, both areas in great need of further study in wildlife species.

Assessment of the stress response in Columbian ground squirrels: laboratory and field validation of an enzyme immunoassay for fecal cortisol metabolites

Stress responses play a critical role in the ecology and demography of wild animals, and the analysis of fecal hormone metabolites is a powerful noninvasive method to assess the role of stress. We characterized the metabolites of injected radiolabeled cortisol in the urine and feces of Columbian ground squirrels and validated an enzyme immunoassay for measuring fecal cortisol metabolites (FCM) with a 5 alpha-3beta,11 beta-diol structure by stimulation and suppression of adrenocortical activity and by evaluation of the circadian pattern of FCM excretion. In addition, we also evaluated the impact of capture, handling, and acclimation to the laboratory on FCM. Cortisol is highly metabolized, with virtually none being excreted, and of the radiolabeled cortisol injected, 31% was recovered in urine and 6.5% in feces. The lag time between cortisol injection and its appearance in urine and feces was 4.5 +/- 0.82 (SE) h and 7.0 +/- 0.53 (SE) h, respectively. FCM levels varied over the day, reflecting circadian variation in endogenous cortisol. Dexamethasone decreased FCM levels by 33%, and ACTH increased them by 255%. Trapping and housing initially increased FCM levels and decreased body mass, but these reversed within 3-7 d, indicating acclimation. Finally, FCM levels were modestly repeatable over time (r=0.57) in wild, live trapped, nonbreeding animals, indicating that FCMs provide a measure of the squirrel's stress-axis state. This assay provides a robust noninvasive assessment of the stress response of the Columbian ground squirrel and will facilitate an integration of its life history and physiology.

Determination of adrenal steroids by microfluidic chip using micellar electrokinetic chromatography

This paper describes a sensitive and convenient method to separate progesterone, 17alpha-hydroxy progesterone, cortexolone, hydrocortisone and cortisone, all of which are steroids and have similar structures, using microfluidic chip-based technology with UV detection at 252 nm. We successfully obtained high-speed separation of the five steroids within 70 s in optimized microfluidic controls and micellar electrokinetic chromatography (MEKC) separation conditions. Fairly good linearity with correlation coefficient of over 0.98 from 10 or 20 to 100 mg/l steroid chemicals was obtained. The limits of detection obtained at a signal to noise ratio of 3 were from 3.89 to 7.80 mg/l. The values of the relative standard deviation (RSD) were 0.98-1.34% for repetitive injection (n = 12) and the intraday and interday RSDs were below 6%. The highly stable response reflected the feasibility of this method.

Seasonal and social influences on fecal androgen and glucocorticoid excretion in wild male long-tailed macaques (Macaca fascicularis)

Whereas it is well known that in strictly seasonal breeding primates (income breeders), alike other vertebrates, males show pronounced changes in testicular and adrenal hormone levels concurrent with reproductive activity, hormonal patterns in males of non-strictly seasonal breeding primate species (capital breeders) and their relation to seasonal and social correlates remain largely unknown. In the present study, we examined the annual pattern of fecal androgen and glucocorticoid excretion and their relationship to environmental (rainfall, temperature) and social factors (number of cycling females, male aggression and copulation rates, male dominance rank) in a group of wild long-tailed macaques (Macaca fascicularis), a species with a moderate degree of reproductive seasonality and classified as capital breeder. The study was carried out in the Gunung Leuser National Park, North Sumatra, Indonesia over a period of ten months encompassing the conception and the birth season. Our results show that male long-tailed macaques exhibit a distinct annual variation in both androgen and glucocorticoid levels. Androgen (but not glucocorticoid) levels were significantly elevated during the conception period in association with elevated rates of male-male aggression and copulatory activity, both strongly related to the number of cycling females in the group. Neither glucocorticoid nor androgen levels were related to male dominance rank or to the environmental parameters investigated. Interestingly, levels of both hormones started to increase in the late birth season and thus 1-2 months prior to the mating season, suggesting that male long-tailed macaques go through pre-breeding hormonal changes in preparation for prospective challenges. Our data thus provide the first evidence that males of a non-strictly seasonal breeding species/capital breeder show endocrine patterns generally similar to those found in strictly seasonal/income breeders.

Population and individual elephant response to a catastrophic fire in Pilanesberg National Park

In predator-free large herbivore populations, where density-dependent feedbacks occur at the limit where forage resources can no longer support the population, environmental catastrophes may play a significant role in population regulation. The potential role of fire as a stochastic mass-mortality event limiting these populations is poorly understood, so too the behavioural and physiological responses of the affected animals to this type of large disturbance event. During September 2005, a wildfire resulted in mortality of 29 (18% population mortality) and injury to 18, African elephants in Pilanesberg National Park, South Africa. We examined movement and herd association patterns of six GPS-collared breeding herds, and evaluated population physiological response through faecal glucocorticoid metabolite (stress) levels. We investigated population size, structure and projected growth rates using a simulation model. After an initial flight response post-fire, severely injured breeding herds reduced daily displacement with increased daily variability, reduced home range size, spent more time in non-tourist areas and associated less with other herds. Uninjured, or less severely injured, breeding herds also shifted into non-tourist areas post-fire, but in contrast, increased displacement rate (both mean and variability), did not adjust home range size and formed larger herds post-fire. Adult cow stress hormone levels increased significantly post-fire, whereas juvenile and adult bull stress levels did not change significantly. Most mortality occurred to the juvenile age class causing a change in post-fire population age structure. Projected population growth rate remained unchanged at 6.5% p.a., and at current fecundity levels, the population would reach its previous level three to four years post-fire. The natural mortality patterns seen in elephant populations during stochastic events, such as droughts, follows that of the classic mortality pattern seen in predator-free large ungulate populations, i.e. mainly involving juveniles. Fire therefore functions in a similar manner to other environmental catastrophes and may be a natural mechanism contributing to population limitation. Welfare concerns of arson fires, burning during “hot-fire” conditions and the conservation implications of fire suppression (i.e. removal of a potential contributing factor to natural population regulation) should be integrated into fire management strategies for conservation areas.

Androgen and glucocorticoid levels reflect seasonally occurring social challenges in male redfronted lemurs (Eulemur fulvus rufus)

Intense reproductive competition and social instability are assumed to increase concentrations of glucocorticoids and androgens in vertebrates, as a means of coping with these challenges. In seasonally breeding redfronted lemurs (Eulemur fulvus rufus), the mating and the birth season and the associated increased male competition are predicted to pose such reproductive challenges. In this paper, we investigate seasonal variation in hormone excretion in male redfronted lemurs, and examine whether this variation is associated with social or ecological factors. Although dominance status has been shown to affect individual stress levels across many taxa, we predicted no rank-related differences in glucocorticoids for redfronted lemurs because relatively equal costs are associated with both high and low rank positions (based on patterns of rank acquisition/maintenance and threats toward subordinates). Over a 14-month period, we collected behavioral data (1843 focal hours) and 617 fecal samples from 13 redfronted lemur males in Kirindy Forest/Madagascar. We found no general rank-related pattern of testosterone or glucocorticoid excretion in this species. Both hormones were excreted at significantly higher levels during the mating and the birth season, despite social stability during both periods. The elevated mating season levels may be explained by increased within-group reproductive competition during this time and are in line with previous studies of other seasonally reproducing primates. For the birth season increase, we propose that the predictable risk of infanticide in this highly seasonal species affects male gonadal and adrenal endocrine activity. We evaluate alternative social and ecological factors influencing the production of both hormone classes and conclude based on our preliminary investigations that none of them can account for the observed pattern.

A case study: fecal corticosteroid and behavior as indicators of welfare during relocation of an Asian elephant

This study was a preliminary investigation of an enzyme immunoassay for measuring fecal glucocorticoid metabolites in a male Asian elephant (Elephas maximus) by investigating changes in behavior and cortisol metabolite excretion associated with a putative stressful event. The study collected fecal samples for 10 days prior to, and 10 days after, 24-hr transport and relocation of the elephant to a new herd. The study measured cortisol metabolites using 2 enzyme immunoassays indicating a 389% and 340% increase in cortisol metabolite excretion following relocation. Maximal cortisol metabolite excretion occurred 2 days after relocation and remained elevated during establishment of the new herd. Stereotypic behavior increased approximately 400% after relocation. The relocation disturbed sleep patterns, the elephant spent less time sleeping during the night, and the elephant slept standing up. These results provide preliminary evidence that noninvasive monitoring of fecal cortisol metabolites can be used to investigate adrenal activity in Asian elephants and may be a safe, practical, and accurate welfare indicator.

Influence of reproductive season and rank on fecal glucocorticoid levels in free-ranging male Verreaux's sifakas (Propithecus verreauxi)

Studies in anthropoid primates and other mammals suggest that reproductive season, rank, reproductive skew, aggression received, and social support are the major factors influencing glucocorticoid output. In which way these are also affecting adrenal function in lemurid primates has been studied rarely. Here, we examine the influence of reproductive season and rank on glucocorticoid output in male sifakas (Propithecus verreauxi), a species characterized by high breeding seasonality, a hierarchy among males and extreme reproductive skew towards dominant males. We established a fecal assay for non-invasively monitoring adrenal activity and collected 315 fecal samples during the reproductive and birth season from 10 male sifakas living in 5 groups in Western Madagascar. We found a significant effect of season on glucocorticoid output, with males exhibiting higher fecal glucocorticoid levels during the reproductive compared to the birth season in conjunction with an increase in overall aggression rates during the former period. Moreover, our data indicate a significant effect of rank on adrenocortical activity with dominant males exhibiting higher glucocorticoid levels than subordinate males in the reproductive season. However, dominant males did not differ significantly in rates of initiated or received aggression and rates of affiliative behavior from subordinates but showed significantly lower rates of submission. Given their highly formalized dominance relationships, we conclude that higher glucocorticoid output in dominant males during the 4-month reproductive season is likely related to higher energetic demands necessary to cope with the challenges of male reproduction rather than to physical demands of increased fighting frequency to maintain dominance status. High rank in sifakas may thus carry high costs, which, however, may be outweighed by monopolization of almost all paternities. In sum, our data generally support the findings on the relationship between environmental and social factors and glucocorticoid output found in non-lemurid primates.

Comparative endocrinology of testicular, adrenal and thyroid function in captive Asian and African elephant bulls

Concentrations of serum testosterone, cortisol, thyroxine (free and total T4), triiodothyronine (free and total T3) and thyroid stimulating hormone (TSH) were measured to assess adrenal and thyroid function as they relate to testicular activity and musth in captive elephants. Blood samples were collected approximately weekly from Asian (n=8) and African (n=12) bulls at seven facilities for periods of 4 months to 9.5 years. Age ranges at study onset were 8-50 years for Asian and 10-21 years for African elephants. Based on keeper logs, seven Asian and three African bulls exhibited behavioral and/or physical (temporal gland secretion, TGS, or urine dribbling, UD) signs of musth, which lasted 2.8+/-2.5 months in duration. Serum testosterone was elevated during musth, with concentrations often exceeding 100 ng/ml. Patterns of testosterone secretion and musth varied among bulls with no evidence of seasonality (P>0.05). Only three bulls at one facility exhibited classic, well-defined yearly musth cycles. Others exhibited more irregular cycles, with musth symptoms often occurring more than once a year. A number of bulls (1 Asian, 9 African) had consistently low testosterone (<10 ng/ml) and never exhibited significant TGS or UD. At facilities with multiple bulls (n=3), testosterone concentrations were highest in the oldest, most dominant male. There were positive correlations between testosterone and cortisol for six of seven Asian and all three African males that exhibited musth (range, r=0.23-0.52; P<0.05), but no significant correlations for bulls that did not (P>0.05). For the three bulls that exhibited yearly musth cycles, TSH was positively correlated (range, r=0.22-0.28; P<0.05) and thyroid hormones (T3, T4) were negatively correlated (range, r=-0.25 to -0.47; P<0.05) to testosterone secretion. In the remaining bulls, there were no clear relationships between thyroid activity and musth status. Overall mean testosterone and cortisol concentrations increased with age for all bulls combined, whereas thyroid activity declined. In summary, a number of bulls did not exhibit musth despite being of adequate physical maturity. Cortisol and testosterone were correlated in most bulls exhibiting musth, indicating a possible role for the adrenal gland in modulating or facilitating downstream responses. Data were generally inconclusive as to a role for thyroid hormones in male reproduction, but the finding of discrete patterns in bulls showing clear testosterone cycles suggests they may facilitate expression or control of musth in some individuals.

Fecal glucocorticoids and their metabolites as indicators of stress in various mammalian species: a literature review

Conservation medicine is a discipline in which researchers and conservationists study and respond to the dynamic interplay between animals, humans, and the environment. From a wildlife perspective, animal species are encountering stressors from numerous sources. With the rapidly increasing human population, a corresponding increased demand for food, fuel, and shelter; habitat destruction; and increased competition for natural resources, the health and well-being of wild animal populations is increasingly at risk of disease and endangerment. Scientific data are needed to measure the impact that human encroachment is having on wildlife. Nonbiased biometric data provide a means to measure the amount of stress being imposed on animals from humans, the environment, and other animals. The stress response in animals functions via glucocorticoid metabolism and is regulated by the hypothalamic-pituitary-adrenal axis. Fecal glucocorticoids, in particular, may be an extremely useful biometric test, since sample collection is noninvasive to subjects and, therefore, does not introduce other variables that may alter assay results. For this reason, many researchers and conservationists have begun to use fecal glucocorticoids as a means to measure stress in various animal species. This review article summarizes the literature on many studies in which fecal glucocorticoids and their metabolites have been used to assess stress levels in various mammalian species. Variations between studies are the main focus of this review. Collection methods, storage conditions, shipping procedures, and laboratory techniques utilized by different researchers are discussed.

Stress hormones in mammals and birds: comparative aspects regarding metabolism, excretion, and noninvasive measurement in fecal samples

A multitude of endocrine mechanisms are involved in coping with challenges. Front-line hormones to overcome stressful situations are glucocorticoids (GCs) and catecholamines (CAs). These hormones are usually determined in plasma samples as parameters of adrenal activity and thus of disturbance. GCs (and CAs) are extensively metabolized and excreted afterwards. Therefore, the concentration of GCs (or their metabolites) can be measured in various body fluids or excreta. Above all, fecal samples offer the advantages of easy collection and a feedback-free sampling procedure. However, large differences exist among species regarding the route and time course of excretion, as well as the types of metabolites formed. Based on information gained from radiometabolism studies (reviewed in this paper), we recently developed and successfully validated different enzyme immunoassays that enable the noninvasive measurement of groups of cortisol or corticosterone metabolites in animal feces. The determination of these metabolites in fecal samples can be used as a powerful tool to monitor GC production in various species of domestic, wildlife, and laboratory animals.

Comparison of different enzyme-immunoassays for assessment of adrenocortical activity in primates based on fecal analysis

Most studies published to date that used fecal glucocorticoid measurements to assess adrenocortical activity in primate (and many nonprimate) species applied a specific cortisol or corticosterone assay. However, since these native glucocorticoids are virtually absent in the feces of most vertebrates, including primates, the validity of this approach has recently been questioned. Therefore, the overall aim of the present study was to assess the validity of four enzyme-immunoassays (EIAs) using antibodies raised against cortisol, corticosterone, and reduced cortisol metabolites (two group-specific antibodies) for assessing adrenocortical activity using fecal glucocorticoid metabolite (GCM) measurements in selected primate species (marmoset, long-tailed macaque, Barbary macaque, chimpanzee, and gorilla). Using physiological stimulation of the hypothalamo-pituitary-adrenocortical (HPA) axis by administering exogenous ACTH or anesthesia, we demonstrated that at least two assays detected the predicted increase in fecal GCM levels in response to treatment in each species. However, the magnitude of response varied between assays and species, and no one assay was applicable to all species. While the corticosterone assay generally was of only limited suitability for assessing glucocorticoid output, the specific cortisol assay was valuable for those species that (according to high-performance liquid chromatography (HPLC) analysis data) excreted clearly detectable amounts of authentic cortisol into the feces. In contrast, in species in which cortisol was virtually absent in the feces, group-specific assays provided a much stronger signal, and these assays also performed well in the other primate species tested (except the marmoset). Collectively, the data suggest that the reliability of a given fecal glucocorticoid assay in reflecting activity of the HPA axis in primates clearly depends on the species in question. Although to date there is no single assay system that can be used successfully across species, our data suggest that group-specific assays have a high potential for cross-species application. Nevertheless, regardless of which GC antibody is chosen, our study clearly reinforces the necessity of appropriately validating the respective assay system before it is used.

Conservation and behavioral neuroendocrinology

The total number of threatened species of vertebrates is likely to be more than 10,000, with approximately one quarter of the world's mammal species, one eighth of the birds and one third of the amphibians threatened with extinction. The rate of loss of animal species and hence of biodiversity is increasing and may become even greater as ecosystems become affected by climate change due to global warming. Behavioral neuroendocrinology, which considers interactions between behavior and neuroendocrine function in animals from all vertebrate taxa, can contribute to animal conservation. Research with laboratory animals can address questions in basic biology relevant to conservation and develop methods for use with threatened animals. Field work with free-living animals considers the basic biology of new species and the use of endocrine tools to assess the susceptibility of species to threats. Non-invasive measurements of hormone concentrations, especially fecal steroids, are extensively used to assess reproductive function and the stress status of animals in captive breeding programs and in the wild. Biodiversity and natural selection both depend on individual variation, and conservation programs often work with animals on an individual basis. The consideration of data from individuals is essential in conservation endocrinology. Direct contributions to conservation programs are challenging as study situations are determined by practical conservation concerns. Indirect contributions such as the provision of scientific input to conservation plans and participation in public education programs offer significant benefits for conservation programs. Directly and indirectly, there are many opportunities for behavioral neuroendocrinologists to contribute to conservation.

Measuring fecal glucocorticoid metabolites in mammals and birds: the importance of validation

In recent years, the noninvasive monitoring of steroid hormone metabolites in feces of mammals and droppings of birds has become an increasingly popular technique. It offers several advantages and has been applied to a variety of species under various settings. However, using this technique to reliably assess an animal's adrenocortical activity is not that simple and straightforward to apply. Because clear differences regarding the metabolism and excretion of glucocorticoid metabolites (GCMs) exist, a careful validation for each species and sex investigated is obligatory. In this review, general analytical issues regarding sample storage, extraction procedures, and immunoassays are briefly discussed, but the main focus lies on experiments and recommendations addressing the validation of fecal GCM measurements in mammals and birds. The crucial importance of scrutinizing the physiological and biological validity of fecal GCM analyses in a given species is stressed. In particular, the relevance of the technique to detect biologically meaningful alterations in adrenocortical activity must be shown. Furthermore, significant effects of the animals' sex, the time of day, season, and different life history stages are discussed, bringing about the necessity to seriously consider possible sex differences as well as diurnal and seasonal variations. Thus, comprehensive information on the animals' biology and stress physiology should be carefully taken into account. Together with an extensive physiological and biological validation, this will ensure that the measurement of fecal GCMs can be used as a powerful tool to assess adrenocortical activity in diverse investigations on laboratory, companion, farm, zoo, and wild animals.

Physical, Physiological, and Behavioral Correlates of Musth in Captive African Elephants (Loxodonta africana)

Although musth in male African elephants (Loxodonta africana) is known to be associated with increased aggressiveness, urine dribbling (UD), temporal gland secretion (TGS), and elevated androgens, the temporal relationship between these changes has not been examined. Here, we describe the pattern of musth-related characteristics in 14 captive elephant bulls by combining long-term observations of physical and behavioral changes with physiological data on testicular and adrenal function. The length of musth periods was highly variable but according to our data set not related to age. Our data also confirm that musth is associated with elevated androgens and, in this respect, show that TGS and UD are downstream effects of this elevation, with TGS responding earlier and to lower androgen levels than UD. Because the majority of musth periods were associated with a decrease in glucocorticoid levels, our data also indicate that musth does not represent a physiological stress mediated by the hypothalamic-pituitary-adrenal axis. Furthermore, we demonstrate that the occurrence of musth is associated with increased aggression and that this is presumably androgen mediated because aggressive males had higher androgen levels. Collectively, the information generated contributes to a better understanding of what characterizes and initiates musth in captive African elephants and provides a basis for further studies designed to examine in more detail the factors regulating the intensity and duration of musth.

The sexually active states of free-ranging male African elephants (Loxodonta africana): defining musth and non-musth using endocrinology, physical signals, and behavior

Musth in male African elephants, Loxodonta africana, is associated with increased aggressive behavior, continuous discharge of urine, copious secretions from the swollen temporal glands, and elevated androgen levels. During musth, bulls actively seek out and are preferred by estrous females although sexual activity is not restricted to the musth condition. The present study combines recently established methods of fecal hormone analysis with long-term observations on male-female associations as well as the presence and intensity of physical signals to provide a more detailed picture about the physical, physiological, and behavioral characteristics of different states of sexual activity in free-ranging African elephants. Based on quantitative shifts in individual bull association patterns, the presence of different physical signals, and significant differences in androgen levels, a total of three potential sub-categories for sexually active bulls could be established. The results demonstrate that elevations in androgen levels are only observed in sexually active animals showing temporal gland secretion and/or urine dribbling, but are not related to the age of the individual. Further, none of the sexually active states showed elevated glucocorticoid output indicating that musth does not represent an HPA-mediated stress condition. On the basis of these results, we suggest that the term "musth" should be exclusively used for the competitive state in sexually active male elephants and that the presence of urine dribbling should be the physical signal used for defining this state.

Use of fecal glucocorticoid metabolite measures in conservation biology research: considerations for application and interpretation

Fecal glucocorticoid metabolite analyses are increasingly being used by a variety of scientists (e.g., conservation biologists, animal scientists) to examine glucocorticoid (i.e., stress hormone) secretion in domestic and wild vertebrates. Adrenocortical activity (i.e., stress response) is of interest to conservation biologists because stress can alter animal behavior, reduce resistance to disease, and affect population performance. The noninvasiveness of fecal-based assessments is attractive, particularly when studying endangered species, because samples can often be obtained without disturbing the animal. Despite such advantages, many confounding factors inhibit the utility of this technique in addressing conservation problems. In particular, interpretation of fecal glucocorticoid metabolite (FGM) measures may be confounded by the length of time animals are held in captivity, normal seasonal and daily rhythms, body condition, sample storage and treatment techniques, diet of the animal, assay selection, animal status (i.e., social ranking, reproductive status), sample age and condition, and sample mass. Further complicating interpretation and utility of these measures is the apparent species-specific response to these factors. The purpose of this paper is to discuss the factors that confound interpretation of FGM measures, summarize research that addresses these issues, and offer an agenda for future research and interpretation. We urge conservation biologists to carefully consider confounding factors and the relationship between FGM secretion and population performance and biological costs when investigating effects of environmental and human-induced disturbances on wildlife. The crisis nature of many decisions in conservation biology often requires decisions from limited data; however, confirmatory results should not be posited when data are incomplete or confounding factors are not understood. Building reliable databases, and research with surrogate species when possible, will aid future efforts and enhance the utility of FGM assays.