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J Med Primatol. Author manuscript; available in PMC 2017 August 01. Published in final edited form as: J Med Primatol. 2016 August ; 45(4): 180–188. doi:10.1111/jmp.12220.
Factors Influencing Alopecia and Hair Cortisol in Rhesus Macaques (Macaca mulatta) Corrine K. Lutz1, Kris Coleman2, Julie M. Worlein3, Rose Kroeker3, Mark T. Menard4, Kendra Rosenberg4, Jerrold S. Meyer4, and Melinda A. Novak4 1Southwest
National Primate Research Center, Texas Biomedical Research Institute, P.O. Box 760549, San Antonio, TX 78245, USA
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2Oregon
National Primate Research Center, University of Massachusetts- Amherst
3Washington
National Primate Research Center, University of Massachusetts- Amherst
4Department
of Psychological and Brain Sciences, University of Massachusetts- Amherst
Abstract Background—Alopecia can occur in captive nonhuman primates, but its etiology is poorly understood. The purpose of this study was to assess alopecia and hair cortisol in rhesus monkeys and to identify potential risk factors.
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Methods—Subjects were 117 rhesus monkeys at two National Primate Research Centers. Photographs and hair samples were obtained during routine physicals. Photographs were analyzed using Image J software to calculate hair loss, and hair samples were assayed for cortisol. Results—Age, days singly housed, and their interactions contributed to the alopecia model for both facilities. Sex and location changes contributed to the hair cortisol model for Facility 1; sedations contributed for Facility 2. Alopecia and hair cortisol were associated at Facility 1. Conclusions—Captive management practices can affect alopecia and hair cortisol. However, there are facility differences in the relationship between alopecia and hair cortisol and in the effect of intrinsic variables and management procedures. Keywords Captive Environment; Facility Differences; Hair Loss; Nonhuman primate; Stress
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Introduction Alopecia, or hair loss, is a common occurrence in captive macaque populations. The extent of hair loss can range from small focal areas to large portions of the body missing hair. Recent studies have reported that as many as 34–86.5% of laboratory-housed rhesus
Corresponding Author: Corrine Lutz, Ph.D., Southwest National Primate Research Center, Texas Biomedical Research Institute, P.O. Box 760549, San Antonio, TX 78245-0549, [email protected], Telephone: 210-258-9729. This work was performed at the Southwest National Primate Research Center, Texas Biomedical Research Institute, San Antonio, TX, USA and at the Oregon National Primate Research Center, Beaverton, OR, USA
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monkeys (Macaca mulatta) have exhibited some form of alopecia; however most of these cases are considered mild [21, 25, 30, 37]. Conditions associated with hair loss in nonhuman primates are varied and may include such factors as pregnancy, stress, aging, behavior (e.g., pulling hair from self or others), disease, housing condition, social rank, and seasonal molting [4, 13, 21, 22, 24, 25, 31, 39]. Although the true impact of hair loss on animal welfare is unknown, it may be indicative of other underlying conditions that affect an animal’s wellbeing. Therefore, it is important to assess potential risk factors to better understand alopecia in captive nonhuman primates.
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Many risk factors associated with alopecia in macaque monkeys are naturally occurring and are not associated with husbandry practices. These may include the animal’s age, sex, and pregnancy status. For example, the extent of alopecia tends to increase with age [4, 21, 31]. Infants have almost no alopecia [38], while geriatric monkeys often have skin abnormalities such as skin lesions, focal scaling, wrinkling, and epidermal thickness, along with alopecia [19]. This association between age and alopecia is not consistent, however. In one study, there was no significant age difference between animals with and without alopecia [24], and in another study, older adult animals (over 10 years) actually had lower levels of alopecia when compared to younger adult animals (4–10 years) [22]. With respect to sex differences, females are typically reported to exhibit greater levels of alopecia than are males [8, 21, 22, 25, 38]. This may be due in part to pregnancy; pregnant females often have significantly poorer coats than non-pregnant females, and hair loss is greatest during the final months of pregnancy and the month following parturition [4, 13]. Hair re-growth then occurs shortly after parturition [13]. However, not all populations of macaque monkeys show such a directional sex difference in alopecia. In some macaque populations there was no sex difference [9, 25], while another study reported that significantly more males were alopecic [24].
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Housing conditions can also have an impact on alopecia. For example, animals housed outdoors had a better coat quality than those housed indoors or in indoor/ outdoor enclosures [38]. Similarly, animals raised indoors had a higher incidence of alopecia than those originating from an outdoor colony but subsequently housed indoors under identical conditions [21]. The enclosure itself can also have an impact on alopecia. For example, lateralized alopecia and specific patterns of hair loss can be friction-induced and associated with the pressure of leaning against cage surfaces [30, 42], and monkeys had significantly worse hair coats when housed on a gravel substrate than when housed on a grass substrate. This could be due to more time spent grooming and less time foraging on the gravel substrate [3, 4]. Social housing can have a positive effect on an animal’s hair coat. For example, being pair-housed was significantly related to decreased alopecia [22], and animals that moved into group or pair-housing or had their cohort changed showed favorable improvement in alopecia [17]. However, animal density within the enclosure can play a role in the extent of alopecia. Although coat condition was not affected solely by the size of the social group [38], an increase in animal density increased levels of alopecia as well as the effect of pregnancy on alopecia [4, 38]. Some cases of alopecia may be self-induced. Significantly more animals with alopecia were reported to hair pull than those with little or no hair loss [24], and more severe alopecia
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scores were associated with hair-pulling [22]. However, although the animals that hairpulled were more likely to exhibit alopecia, the incidence of hair pulling was significantly lower than that of alopecia, and hair pulling explained only a small portion of the total variance in alopecia [25]. In addition, histological findings indicative of hair-pulling were present in only a small number of rhesus monkeys [37]. In animals with a history of hairpulling, the location of the hair being plucked and the location of alopecia are not always the same, and 13% of control animals without alopecia were also observed to hair-pull [24]. Although the pattern of hair loss may be associated with the method of hair pulling such as plucking, pulling, or overgrooming [14], rates of self-grooming were not significantly different between animals with and without alopecia, suggesting that grooming alone is not a significant cause of alopecia [42]. Although hair was found in 21% of fecal samples, the presence of hair in the feces was also not related to coat quality [38]. However, if the hair that is pulled is ingested, it can lead to trichobezoars and potentially serious complications [28].
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There are mixed results regarding the association between alopecia and stress. Cortisol is a factor of the physiological response to stress in primates, and the measurement of hair cortisol concentrations can be utilized as a measure of chronic stress [12]. In a multi-facility study, Novak et al. [2014] reported an overall positive association between hair cortisol and alopecia in single or pair-housed rhesus monkeys, but this was not true for all of the facilities when tested separately. Hair cortisol was also not associated with hair loss in group-housed animals [36]. In addition, animals with alopecia did not exhibit indicators of stress such as hyperglycemia, hypercortisolemia, or a stress leukogram [24] and animals with a damaged coat actually had lower fecal glucocorticoid levels than those with no alopecia [38].
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The purpose of this study was to assess alopecia, hair cortisol, and their relationship, in rhesus monkeys housed at two primate facilities and to evaluate the impact of both intrinsic variables such as sex and age, as well as recent environmental experiences such as sedation events, relocation, and single housing. These independent variables have previously been identified and/or assessed as potential risk factors for abnormal behavior in rhesus macaques [26] and are of interest as potential risk factors for alopecia and cortisol levels as well. This information will help us to better understand alopecia in macaque populations and to better direct animal management procedures.
Materials and Methods Humane Care Guidelines
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Both primate facilities are accredited by AAALAC, International and all work was approved by the local Institutional Animal Care and Use Committees (IACUC). The research was performed in accordance with the Animal Welfare Act and the U.S. Department of Health and Human Services Guide for the Care and Use of Laboratory Animals (2011). Subjects The subjects were 117 rhesus monkeys (Macaca mulatta) housed at two National Primate Research Centers, the Southwest National Primate Research Center (SNPRC) in San
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Antonio, TX and the Oregon National Primate Research Center (ONPRC) in Beaverton, OR. Sampling procedures differed between the two facilities. At Facility 1 (N = 34, 17 males), animals judged to have high levels of alopecia (N = 14) or little to no alopecia (N = 20) based on staff visual inspection were identified for study selection. At Facility 2 (N = 83, 31 males), animals were selected for the study based on availability for photo and hair sampling without regard to alopecia status.
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At the time of sample collection, the subjects were housed indoors individually (n = 87) or paired (n = 30) in size-appropriate caging (approximately 1.3–2.4 m2 per animal), and were maintained in accordance with the Guide for the Care and Use of Laboratory Animals (2011). The monkeys were fed a nutritionally complete diet supplemented with additional fruits, vegetables, and grains. All animals were included in the facilities’ environmental enrichment programs and were routinely provided with perches, toys, foraging devices, and novel food items. Alopecia Measurement The animals were photographed opportunistically while they were sedated for routine physical exams. Three orientations were photographed: left, right, and prone. The photographs were analyzed using the Image J image processing program (NIH). The dark coat of the body was outlined, and brightness thresholds were adjusted highlighting the areas of alopecia in red. Total percent hair loss on the body was then calculated [30]. To reduce variability, all photographs were processed and analyzed at a single facility (University of Massachusetts- Amherst). During the physical exams, none of the subjects were noted to have a clinical condition that would normally result in hair loss.
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Hair Cortisol Measurement After the photographs were taken, hair was gently shaved from the back of the neck, wrapped in aluminum foil packets and stored in a freezer until shipment to the University of Massachusetts-Amherst for processing. Hair was assayed for cortisol according to the procedures described in Davenport et al. [2006]. Colony Records Colony record information of the subjects was then analyzed. Variables extracted from the colony records included the animals’ sex and age. In addition, the following data were recorded from the 365 days prior to sampling: the number of days the animal was singly housed, the number of sedations performed on the animal, and the number of location changes (between rooms or buildings) the animal experienced.
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Data Analysis Demographic Variables—Separate t-tests were conducted to examine facility differences in age, number of days singly housed, number of sedations, and number of location changes. Because of the facility differences in sampling procedures and demographic variables, further analyses were conducted separately for each facility. Correlations were then conducted on the demographic variables to identify potential relationships between the independent variables at each facility. J Med Primatol. Author manuscript; available in PMC 2017 August 01.
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Alopecia—For Facility 1, a logistic regression was conducted to examine the potential effects of the demographic variables (sex, age, days singly housed, number of sedations, number of location changes) on alopecia classification (high vs. low). For Facility 2, a linear regression was conducted to compare the potential effects of the same demographic variables on alopecia level. Hair Cortisol—Linear regressions were used to examine the potential effects of the demographic variables on hair cortisol. Because of the subject selection procedures based on alopecia at Facility 1, we also entered alopecia level categorization as the first predictor in the linear regression for that facility. Alopecia level was retained in the model regardless of significance while all other variables were tested for their model contribution. In this way, we explored the variance between hair cortisol and the demographic variables separately within the high and low alopecia groups at Facility 1.
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For all of the above regressions, all variables and the interactions of all variables with the number of days singly housed were initially entered into the model. A backwards elimination procedure was used to determine the ‘best fit’ model. Variables were assessed for their contribution to the model by evaluating the change in total variance accounted for (R squared) when that term was removed. Terms with the highest p-values were removed first. If a term did not show a significant main effect but contributed to a significant interaction, the main and interactive effects for that term were tested as a block for their combined contribution to the model variance. They remained in the model only if this combined contribution was significant.
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Relationship between Alopecia and Hair Cortisol—For Facility 1, a t-test was conducted to compare levels of hair cortisol across the high and the low alopecia categories. For Facility 2, a Pearson correlation was conducted to identify a potential relationship between alopecia and hair cortisol.
Results Demographic Variables The overall mean animal age was 9.3 (range = 3–21). There was no facility difference in age of the subjects (t(115) = 1.247, P = 0.22) or in the number of sedations the animal experienced during the past year (t(115) = 0.195, P = 0.85; Table 1). However, the number of days the animals were singly housed during the prior year was greater at Facility 1 (t(115) = 2.274, P < 0.05) while the number of location changes the animals experienced during the prior year was greater at Facility 2 (t(115) = −3.909, P < 0.001; Table 1).
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Correlations were conducted on the independent variables for each facility separately. At Facility 1, the number of location changes was negatively correlated with age (r = −0.346, P < 0.05) and days singly housed during the prior year (r = −0.346, P < 0.05). At Facility 2, females were older (r = 0.466, P < 0.001), had more sedations (r = 0.446, P < 0.001) and more location changes (r = 0.268, p < 0.05). In addition, the number of location changes was correlated with the number of days singly housed (r = 0.219, P < 0.05) and age (r = 0.222, P < 0.05).
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Alopecia
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At Facility 1, the subjects in the “high alopecia” group were missing hair from an average of 50.1% of their bodies (range: 16.4 – 85.8%) while the “low alopecia” group subjects were missing hair from an average of 0.32% of their bodies (range: 0–1.44%). At Facility 2, the subjects overall were missing hair from an average of 6.25% of their bodies (range: 0– 38.8%). Age, the number of days singly housed, and the age×number of days singly housed interaction contributed to alopecia expression at both facilities. No other predictors were significant (Table 2). Examination of the raw data and predicted model values revealed a crossover interaction between age and the number of days singly housed. As animals increased in age and days singly housed, the probability of having high levels of alopecia also increased (Figure 1).
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Hair Cortisol At Facility 1, hair cortisol levels averaged 77.7 ± 6.3 pg/mg. Sex and number of location changes contributed significantly to levels of hair cortisol, explaining a total of 44.4% of the variance. Females had higher levels of hair cortisol than males, and animals with more location changes had increased levels of hair cortisol. At Facility 2, the hair cortisol levels averaged 56.1 ± 2.4 pg/mg. The number of sedations was the only predictor of hair cortisol, explaining 28.5% of the variance; animals with more sedations had an increase in hair cortisol levels (Table 2). Relationship between Alopecia and Hair Cortisol
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At Facility 1, animals with high levels of alopecia had significantly higher levels of hair cortisol than did those with low levels of alopecia (98.6 ± 11.8 vs. 63.1 ± 4.8 pg/mg; t(32) = 3.118, p < 0.005), but there was no relationship between alopecia and hair cortisol at Facility 2 (r = −0.117, P = 0.292).
Discussion This study investigated alopecia and hair cortisol at two National Primate Research Centers. Because the subjects were not all randomly selected and because of the cross-center variability in the variables being studied, analyses were conducted separately for each facility and therefore do not indicate true differences in facility populations.
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At Facility 1, the “high alopecia group” had significantly higher levels of hair cortisol than the “low alopecia group”, demonstrating some evidence that alopecia may be associated with hair cortisol levels. However, there was no association at Facility 2, suggesting that alopecia is not a consistent marker of chronic stress as indicated by hair cortisol levels. These differential results are similar to those of Novak et al. (2014), which used some of the same subjects. The reason for this facility difference in association remains unclear and may be due to differences in research protocols, animal management practices (e.g., the number of days the animals were singly housed), or genetic differences in the two populations. Any given relationship between alopecia and cortisol, however, is not necessarily a causal
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relationship. Stress may result in hair loss, but alternatively, hair loss (and its potential effect on thermoregulation) may result in an increase in stress [30]. Hair loss and stress may have interacted differentially at the two facilities, resulting in different outcomes. Sex effect
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Overall, there was no significant effect of sex on alopecia. This result is in contrast to many previous studies on alopecia that report a significant sex difference, typically with more females than males showing hair loss [8, 21 22, 25, 38]. This sex difference has been attributed in part to pregnancy [4, 13]. Although some of the animals in the present study were recently removed from breeding groups, all were housed singly or in non-breeding pairs at the time of data collection, and it is unlikely that any females were pregnant at the time of sampling. Therefore, the lack of sex difference in alopecia may be due in part to an absence of pregnant females in the population. This result is not unique, however. For example, Crockett et al., (2007) also reported no sex difference in alopecia. Sex alone may therefore only play a minor role in the extent of alopecia.
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In contrast, there was a significant effect of sex on hair cortisol; however, this was only evident at Facility 1. Crockett et al. (1993) reported that female longtailed macaques tended to have higher cortisol values than males, especially in response to potentially stressful events such as room change, sedation, and tethering procedures, but the sex difference was reduced once the animals were habituated, suggesting that there may be instead a sex difference in reactivity. The reason for the differing results at the two facilities in the present study is unknown. There was no facility difference in number of sedations, and the subjects at Facility 1 actually had fewer room changes than those at Facility 2. Perhaps the females at Facility 1 were more reactive and/or more greatly affected by housing conditions or research protocols that were not assessed in the present study. Further research in this area needs to be conducted. Age and Single Housing effect
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In previous studies, alopecia has been reported to increase with age [4, 21, 31]; older animals tended to have greater amounts of alopecia and hair thinning than their younger counterparts [19, 31]. However, this relationship is not consistent across studies. For example, Luchins et al. (2011) reported no age effect, and Kroeker et al. (2014) reported that the oldest animals actually had a better coat than the younger adult subjects. In the present study, we found a significant age × number of days singly housed interaction at both facilities. As animals increased in age and the time they were singly housed, the probability of having high levels of alopecia or being in the “high alopecia” category also increased. This finding is perhaps more remarkable since information from only the past year of each animal’s social history was used in the analysis. This age effect may be related to factors such as hair-pulling or friction from cage contact. For example, in a study of singly housed rhesus monkeys, older animals were more likely than younger animals to pull out their own hair [26]. In addition, some patterns of alopecia have been reported to match cage mesh patterns and may be due to the friction caused by leaning against the cage sides [30]. This may be more likely to occur in singly housed and older animals, because they tend to be less active than their socially housed or younger counterparts [2, 34]. Therefore, although hair
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pulling, activity, and cage friction were not directly assessed in the present study, they may have been contributors to hair loss, especially in older animals. Number of Sedations
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The number of sedations during the prior year was not associated with alopecia at either facility. However, it was associated with an increase in hair cortisol at Facility 2. Sedation procedures generally involve capture and/or restraint, which alone can result in activation of the HPA axis. The disorientation that occurs before the animal is fully sedated as well as the temporary discomfort of the injection may also play a role [35]. For example, short-term stress from a single sedation via darting has been shown to increase serum cortisol in chimpanzees (Pan troglodytes) [1]. Sedation has also resulted in an increase in serum cortisol in baboons (Papio spp.) [5] and adult Cebus monkeys (Cebus apella) [23]. However, not all sedations resulted in an increase in cortisol [5, 27, 40]. In a study of adult male rhesus monkeys, cortisol increased in the animals that received three injections of ketamine over a period of two hours, but not in monkeys that received a single injection [33]. One factor that may play a role in different results may be whether the monkeys observed other animals undergo restraint and sedation. In male (but not female) rhesus monkeys there was a positive correlation between levels of plasma cortisol and the order in which they were sedated in a colony room. When the room was arranged so the animals could not see each other, this effect was not observed [15]. Perhaps the different results at the two facilities occurred because of differences in the timing or location of the procedures performed during sedation. In addition, the drugs utilized for sedation may also have played a role. For example, ketamine and Telazol were shown to have differential effects on plasma cortisol. In rhesus macaques, ketamine had little effect on cortisol, but Telazol was shown to reduce cortisol in morning samples [5]. Telazol was involved in 4.3% of the sedations at Facility 1, but only 0.4% of the sedations at Facility 2. Perhaps the type of drug utilized for sedation played some role in the differing results. The effect of sedation on cortisol is complex and may be influenced by a number of factors including sedation procedures, familiarity of the subjects with the procedures, drug type, dose, and time of day [5]. In addition, the reasons for sedation (routine colony maintenance, clinical or research needs, etc.) may themselves have contributed independently to hair cortisol levels. The complexity of and contrasting results in sedation effects on stress demonstrate the need for further study. Number of Location Changes
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The number of location changes during the prior year was not associated with alopecia, but it was associated with an increase in hair cortisol at Facility 1. The movement of an animal to a novel location has been used as a stressor in a number of studies [6, 7, 16]. Although the location changes in the present study were limited to within-facility moves, they included moves either to a different room or to a different building, for husbandry or research purposes. Such relocations included not only changes to the animal’s physical environment, but also to the social environment, as previous social partners are left behind while new social contacts are made. It is therefore not surprising that these moves are also associated with an increase in hair cortisol. The impact of location changes on stress has been reported in a number of cases, with stress increasing as measured both behaviorally and physiologically. Relocation can result in behavioral changes lasting days to weeks after the J Med Primatol. Author manuscript; available in PMC 2017 August 01.
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move [18, 29]. Whether the move is within a facility or between facilities, the impact on the HPA axis is also evident. For example, relocation to a new facility resulted in significantly higher levels of fecal cortisol in Garnett’s bushbabies (Otolemur garnettii) on the day of the move, which returned to baseline one week after the move [41]. Similarly, after moving to a new building within a facility, male rhesus monkeys had significantly elevated serum cortisol levels between one hour to seven days after the move [11, 32], and elevated hair cortisol 4 months post-move [11]. The reason for a difference in results between the two facilities in the present study is unclear. However, the number of location changes at Facility 1 was negatively correlated with age. The younger animals may have been more greatly impacted by the moves than were the older animals. In addition, the number of relocations was significantly greater at Facility 2. Perhaps because of this, each move at this facility had less of an effect on the animals. Some animals at this facility were also moved in groups rather than individually. This may have helped to modulate the stressfulness of relocation, as the presence of a familiar companion has been reported to reduce the stress response [43].
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Conclusion
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The results of this study demonstrate that alopecia is not an uncommon occurrence in populations of captive nonhuman primates and that it is related in part to stress as measured by hair cortisol. However, facility differences were evident in the association between alopecia and cortisol and in risk factors associated with these variables. Although potential contributing factors to these facility differences have not been identified, they may include differences in variables such as husbandry procedures, research protocols, or genetic makeup of the subjects. Both intrinsic and environmental risk factors contributed to levels of alopecia and hair cortisol, but their contributions differed; age and proportion of the year singly housed played significant roles in alopecia, while sex, number of sedations, and number of location changes had a greater impact on hair cortisol. Therefore, alopecia and hair cortisol may be impacted differentially by intrinsic and environmental variables. However, all variables should be considered when making decisions regarding animal management. For example, days singly housed, the number of sedations, and the number of location changes should be limited whenever possible.
Acknowledgments We would like to thank Brittany Peterson (SNPRC), Nicola D. Robertson (ONPRC), and Daniel Gottlieb (ONPRC) for assistance with data collection. This research was supported by grants R24OD01180-15 to Melinda Novak at the University of Massachusetts, P51OD011133 to Texas Biomedical Research Institute (SNPRC), P51OD010425 to WaNPRC, and P51OD011092 to ONPRC.
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23. Lahoz MM, Nagle CA, Porta M, Farinati Z, Manzur TD. Cortisol response and ovarian hormones in juvenile and cycling female Cebus monkeys: effect of stress and dexamethasone. Am J Primatol. 2007; 69:551–561. [PubMed: 17177312] 24. Luchins KR, Baker KC, Gilbert MH, Blanchard JL, Liu DX, Myers L, Bohm RP. Application of the diagnostic evaluation for alopecia in traditional veterinary species to laboratory rhesus macaques (Macaca mulatta). JAALAS. 2011; 50:926–938. [PubMed: 22330789] 25. Lutz CK, Coleman K, Worlein J, Novak MA. Hair loss and hair-pulling in rhesus macaques (Macaca mulatta). JAALAS. 2013; 52:454–457. [PubMed: 23849443] 26. Lutz C, Well A, Novak M. Stereotypic and self-injurious behavior in rhesus macaques: a survey and retrospective analysis of environment and early experience. Am J Primatol. 2003; 60:1–15. [PubMed: 12766938] 27. Malaivijitnond S, Takenaka O, Sankai T, Yoshida T, Cho F, Yoshikawa Y. Effects of single and multiple injections of ketamine hydrochloride on serum hormone concentrations in male cynomolgus monkeys. Lab Anim Sci. 1998; 48:270–274. [PubMed: 10090027] 28. Mook DM. Gastric trichobezoars in a rhesus macaque (Macaca mulatta). Comp Med. 2002; 52:560–562. [PubMed: 12540171] 29. Morimura N, Fujisawa M, Mori Y, Teramoto M. Environmental influences on sleep behavior in captive male chimpanzees (Pan troglodytes). Int J Primatol. 2012; 33:822–829. 30. Novak MA, Hamel AF, Coleman K, Lutz CK, Worlein J, Menard M, Ryan A, Rosenberg K, Meyer JS. Hair loss and hypothalamic-pituitary-adrenocortical axis activity in captive rhesus macaques (Macaca mulatta). JAALAS. 2014; 53:261–266. [PubMed: 24827567] 31. Novak MA, Meyer JS. Alopecia: possible causes and treatments, particularly in captive nonhuman primates. Comp Med. 2009; 59:18–26. [PubMed: 19295051] 32. Phoenix CH, Chambers KC. Sexual behavior and serum hormone levels in aging rhesus males: effects of environmental change. Horm Behav. 1984; 18:206–215. [PubMed: 6735368] 33. Puri CP, Puri V, Anand Kumar TC. Serum levels of testosterone, cortisol, prolactin and bioactive luteinizing hormone in adult male rhesus monkeys following cage-restraint or anaesthetizing with ketamine hydrochloride. Acta Endocrinol. 1981; 97:118–124. [PubMed: 7223311] 34. Ramsey JJ, Laatsch JL, Kemnitz JW. Age and gender differences in body composition, energy expenditure, and glucoregulation of adult rhesus monkeys. J Med Primatol. 2000; 29:11–19. [PubMed: 10870670] 35. Sapolsky RM. The endocrine stress-response and social status in the wild baboon. Horm Behav. 1982; 16:279–292. [PubMed: 6890939] 36. Sarnowski MB, Jacobsen KR, Lambeth SP, Schapiro SJ. A multi-faceted investigation of hair loss in outdoor group-housed rhesus macaques (Macaca mulatta). Am J Primatol. 2013; 75(S 1):61. 37. Steinmetz HW, Kaumanns W, Dix I, Neimeier KA, Kaup FJ. Dermatologic investigation of alopecia in rhesus macaques (Macaca mulatta). J Zoo Wildl Med. 2005; 36:229–238. [PubMed: 17323563] 38. Steinmetz HW, Kaumanns W, Dix I, Heistermann M, Fox M, Kaup FJ. Coat condition, housing condition and measurement of faecal cortisol metabolites- a non-invasive study about alopecia in captive rhesus macaques (Macaca mulatta). J Med Primatol. 2006; 35:3–11. [PubMed: 16430489] 39. Vessey SH, Morrison JA. Molt in free-ranging rhesus monkeys, Macaca mulatta. J Mammal. 1970; 51:89–93. 40. Walker ML, Pepe GJ, Garnett NL, Albrecht ED. Effects of anesthetic agents on the adrenocortical system of female baboons. Am J Primatol. 1987; 13:325–332. 41. Watson SL, McCoy JG, Stavisky RC, Greer TF, Hanbury D. Cortisol response to relocation stress in Garnett’s bushbaby (Otolemur garnettii). Contemp Top. 2005; 44:22–24. 42. West AM, Leland SP, Lorence MA, Welty TM, Wagner WL, Erwin JM. Behavioral correlates of alopecia severity in laboratory rhesus macaques (Macaca mulatta). Am J Primatol. 2008; 70(S1): 51. 43. Winslow JT, Noble PL, Lysons CK, Sterk SM, Insel TR. Rearing effects on cerebrospinal fluid oxytocin concentration and social buffering in rhesus monkeys. Neuropsychopharmacology. 2003; 28:910–918. [PubMed: 12700704]
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Age × Days singly housed interaction for Facility 1 (top) and Facility 2 (bottom). For Facility 2, the alopecia groups (low vs. high) were based on a median split.
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Table 1
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Mean ± SE of each of the variables for the different facilities Variable
Facility 1
Facility 2
Age (Years)
10.1 ± 0.8
9.0 ± 0.4
Number of days singly housed during the prior year*
209.3 ± 24.5
148.9 ± 14.1
Number of sedations during the prior year
6.9 ± 0.7
6.7 ± 0.6
Number of location changes during the prior year*
1.5 ± 0.3
3.9 ± 0.4
*
Significant Facility differences
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Facility 2
Facility 1
b = 28.576 P < 0.01
Hair Cortisol
Facility 2
Facility 1
Alopecia
Sex
b = −1.093 P < 0.005
b = −0.201 P = 0.234
Age
b = −0.054 P < 0.005
b = −0.022 P < 0.05
Number of Days Singly Housed
b = 2.060 P < 0.001
Number of Sedations
b = 6.688 P < 0.05
Number of Location Changes
b = 0.004 P < 0.05
b = 0.002 P < 0.05
Days Singly Housed × Age
Beta values and associated significance levels for terms included in best fit models
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Table 2 Lutz et al. Page 15
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J Med Primatol. Author manuscript; available in PMC 2017 August 01. Published in final edited form as: J Med Primatol. 2016 August ; 45(4): 180–188. doi:10.1111/jmp.12220.
Factors Influencing Alopecia and Hair Cortisol in Rhesus Macaques (Macaca mulatta) Corrine K. Lutz1, Kris Coleman2, Julie M. Worlein3, Rose Kroeker3, Mark T. Menard4, Kendra Rosenberg4, Jerrold S. Meyer4, and Melinda A. Novak4 1Southwest
National Primate Research Center, Texas Biomedical Research Institute, P.O. Box 760549, San Antonio, TX 78245, USA
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2Oregon
National Primate Research Center, University of Massachusetts- Amherst
3Washington
National Primate Research Center, University of Massachusetts- Amherst
4Department
of Psychological and Brain Sciences, University of Massachusetts- Amherst
Abstract Background—Alopecia can occur in captive nonhuman primates, but its etiology is poorly understood. The purpose of this study was to assess alopecia and hair cortisol in rhesus monkeys and to identify potential risk factors.
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Methods—Subjects were 117 rhesus monkeys at two National Primate Research Centers. Photographs and hair samples were obtained during routine physicals. Photographs were analyzed using Image J software to calculate hair loss, and hair samples were assayed for cortisol. Results—Age, days singly housed, and their interactions contributed to the alopecia model for both facilities. Sex and location changes contributed to the hair cortisol model for Facility 1; sedations contributed for Facility 2. Alopecia and hair cortisol were associated at Facility 1. Conclusions—Captive management practices can affect alopecia and hair cortisol. However, there are facility differences in the relationship between alopecia and hair cortisol and in the effect of intrinsic variables and management procedures. Keywords Captive Environment; Facility Differences; Hair Loss; Nonhuman primate; Stress
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Introduction Alopecia, or hair loss, is a common occurrence in captive macaque populations. The extent of hair loss can range from small focal areas to large portions of the body missing hair. Recent studies have reported that as many as 34–86.5% of laboratory-housed rhesus
Corresponding Author: Corrine Lutz, Ph.D., Southwest National Primate Research Center, Texas Biomedical Research Institute, P.O. Box 760549, San Antonio, TX 78245-0549, [email protected], Telephone: 210-258-9729. This work was performed at the Southwest National Primate Research Center, Texas Biomedical Research Institute, San Antonio, TX, USA and at the Oregon National Primate Research Center, Beaverton, OR, USA
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monkeys (Macaca mulatta) have exhibited some form of alopecia; however most of these cases are considered mild [21, 25, 30, 37]. Conditions associated with hair loss in nonhuman primates are varied and may include such factors as pregnancy, stress, aging, behavior (e.g., pulling hair from self or others), disease, housing condition, social rank, and seasonal molting [4, 13, 21, 22, 24, 25, 31, 39]. Although the true impact of hair loss on animal welfare is unknown, it may be indicative of other underlying conditions that affect an animal’s wellbeing. Therefore, it is important to assess potential risk factors to better understand alopecia in captive nonhuman primates.
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Many risk factors associated with alopecia in macaque monkeys are naturally occurring and are not associated with husbandry practices. These may include the animal’s age, sex, and pregnancy status. For example, the extent of alopecia tends to increase with age [4, 21, 31]. Infants have almost no alopecia [38], while geriatric monkeys often have skin abnormalities such as skin lesions, focal scaling, wrinkling, and epidermal thickness, along with alopecia [19]. This association between age and alopecia is not consistent, however. In one study, there was no significant age difference between animals with and without alopecia [24], and in another study, older adult animals (over 10 years) actually had lower levels of alopecia when compared to younger adult animals (4–10 years) [22]. With respect to sex differences, females are typically reported to exhibit greater levels of alopecia than are males [8, 21, 22, 25, 38]. This may be due in part to pregnancy; pregnant females often have significantly poorer coats than non-pregnant females, and hair loss is greatest during the final months of pregnancy and the month following parturition [4, 13]. Hair re-growth then occurs shortly after parturition [13]. However, not all populations of macaque monkeys show such a directional sex difference in alopecia. In some macaque populations there was no sex difference [9, 25], while another study reported that significantly more males were alopecic [24].
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Housing conditions can also have an impact on alopecia. For example, animals housed outdoors had a better coat quality than those housed indoors or in indoor/ outdoor enclosures [38]. Similarly, animals raised indoors had a higher incidence of alopecia than those originating from an outdoor colony but subsequently housed indoors under identical conditions [21]. The enclosure itself can also have an impact on alopecia. For example, lateralized alopecia and specific patterns of hair loss can be friction-induced and associated with the pressure of leaning against cage surfaces [30, 42], and monkeys had significantly worse hair coats when housed on a gravel substrate than when housed on a grass substrate. This could be due to more time spent grooming and less time foraging on the gravel substrate [3, 4]. Social housing can have a positive effect on an animal’s hair coat. For example, being pair-housed was significantly related to decreased alopecia [22], and animals that moved into group or pair-housing or had their cohort changed showed favorable improvement in alopecia [17]. However, animal density within the enclosure can play a role in the extent of alopecia. Although coat condition was not affected solely by the size of the social group [38], an increase in animal density increased levels of alopecia as well as the effect of pregnancy on alopecia [4, 38]. Some cases of alopecia may be self-induced. Significantly more animals with alopecia were reported to hair pull than those with little or no hair loss [24], and more severe alopecia
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scores were associated with hair-pulling [22]. However, although the animals that hairpulled were more likely to exhibit alopecia, the incidence of hair pulling was significantly lower than that of alopecia, and hair pulling explained only a small portion of the total variance in alopecia [25]. In addition, histological findings indicative of hair-pulling were present in only a small number of rhesus monkeys [37]. In animals with a history of hairpulling, the location of the hair being plucked and the location of alopecia are not always the same, and 13% of control animals without alopecia were also observed to hair-pull [24]. Although the pattern of hair loss may be associated with the method of hair pulling such as plucking, pulling, or overgrooming [14], rates of self-grooming were not significantly different between animals with and without alopecia, suggesting that grooming alone is not a significant cause of alopecia [42]. Although hair was found in 21% of fecal samples, the presence of hair in the feces was also not related to coat quality [38]. However, if the hair that is pulled is ingested, it can lead to trichobezoars and potentially serious complications [28].
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There are mixed results regarding the association between alopecia and stress. Cortisol is a factor of the physiological response to stress in primates, and the measurement of hair cortisol concentrations can be utilized as a measure of chronic stress [12]. In a multi-facility study, Novak et al. [2014] reported an overall positive association between hair cortisol and alopecia in single or pair-housed rhesus monkeys, but this was not true for all of the facilities when tested separately. Hair cortisol was also not associated with hair loss in group-housed animals [36]. In addition, animals with alopecia did not exhibit indicators of stress such as hyperglycemia, hypercortisolemia, or a stress leukogram [24] and animals with a damaged coat actually had lower fecal glucocorticoid levels than those with no alopecia [38].
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The purpose of this study was to assess alopecia, hair cortisol, and their relationship, in rhesus monkeys housed at two primate facilities and to evaluate the impact of both intrinsic variables such as sex and age, as well as recent environmental experiences such as sedation events, relocation, and single housing. These independent variables have previously been identified and/or assessed as potential risk factors for abnormal behavior in rhesus macaques [26] and are of interest as potential risk factors for alopecia and cortisol levels as well. This information will help us to better understand alopecia in macaque populations and to better direct animal management procedures.
Materials and Methods Humane Care Guidelines
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Both primate facilities are accredited by AAALAC, International and all work was approved by the local Institutional Animal Care and Use Committees (IACUC). The research was performed in accordance with the Animal Welfare Act and the U.S. Department of Health and Human Services Guide for the Care and Use of Laboratory Animals (2011). Subjects The subjects were 117 rhesus monkeys (Macaca mulatta) housed at two National Primate Research Centers, the Southwest National Primate Research Center (SNPRC) in San
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Antonio, TX and the Oregon National Primate Research Center (ONPRC) in Beaverton, OR. Sampling procedures differed between the two facilities. At Facility 1 (N = 34, 17 males), animals judged to have high levels of alopecia (N = 14) or little to no alopecia (N = 20) based on staff visual inspection were identified for study selection. At Facility 2 (N = 83, 31 males), animals were selected for the study based on availability for photo and hair sampling without regard to alopecia status.
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At the time of sample collection, the subjects were housed indoors individually (n = 87) or paired (n = 30) in size-appropriate caging (approximately 1.3–2.4 m2 per animal), and were maintained in accordance with the Guide for the Care and Use of Laboratory Animals (2011). The monkeys were fed a nutritionally complete diet supplemented with additional fruits, vegetables, and grains. All animals were included in the facilities’ environmental enrichment programs and were routinely provided with perches, toys, foraging devices, and novel food items. Alopecia Measurement The animals were photographed opportunistically while they were sedated for routine physical exams. Three orientations were photographed: left, right, and prone. The photographs were analyzed using the Image J image processing program (NIH). The dark coat of the body was outlined, and brightness thresholds were adjusted highlighting the areas of alopecia in red. Total percent hair loss on the body was then calculated [30]. To reduce variability, all photographs were processed and analyzed at a single facility (University of Massachusetts- Amherst). During the physical exams, none of the subjects were noted to have a clinical condition that would normally result in hair loss.
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Hair Cortisol Measurement After the photographs were taken, hair was gently shaved from the back of the neck, wrapped in aluminum foil packets and stored in a freezer until shipment to the University of Massachusetts-Amherst for processing. Hair was assayed for cortisol according to the procedures described in Davenport et al. [2006]. Colony Records Colony record information of the subjects was then analyzed. Variables extracted from the colony records included the animals’ sex and age. In addition, the following data were recorded from the 365 days prior to sampling: the number of days the animal was singly housed, the number of sedations performed on the animal, and the number of location changes (between rooms or buildings) the animal experienced.
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Data Analysis Demographic Variables—Separate t-tests were conducted to examine facility differences in age, number of days singly housed, number of sedations, and number of location changes. Because of the facility differences in sampling procedures and demographic variables, further analyses were conducted separately for each facility. Correlations were then conducted on the demographic variables to identify potential relationships between the independent variables at each facility. J Med Primatol. Author manuscript; available in PMC 2017 August 01.
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Alopecia—For Facility 1, a logistic regression was conducted to examine the potential effects of the demographic variables (sex, age, days singly housed, number of sedations, number of location changes) on alopecia classification (high vs. low). For Facility 2, a linear regression was conducted to compare the potential effects of the same demographic variables on alopecia level. Hair Cortisol—Linear regressions were used to examine the potential effects of the demographic variables on hair cortisol. Because of the subject selection procedures based on alopecia at Facility 1, we also entered alopecia level categorization as the first predictor in the linear regression for that facility. Alopecia level was retained in the model regardless of significance while all other variables were tested for their model contribution. In this way, we explored the variance between hair cortisol and the demographic variables separately within the high and low alopecia groups at Facility 1.
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For all of the above regressions, all variables and the interactions of all variables with the number of days singly housed were initially entered into the model. A backwards elimination procedure was used to determine the ‘best fit’ model. Variables were assessed for their contribution to the model by evaluating the change in total variance accounted for (R squared) when that term was removed. Terms with the highest p-values were removed first. If a term did not show a significant main effect but contributed to a significant interaction, the main and interactive effects for that term were tested as a block for their combined contribution to the model variance. They remained in the model only if this combined contribution was significant.
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Relationship between Alopecia and Hair Cortisol—For Facility 1, a t-test was conducted to compare levels of hair cortisol across the high and the low alopecia categories. For Facility 2, a Pearson correlation was conducted to identify a potential relationship between alopecia and hair cortisol.
Results Demographic Variables The overall mean animal age was 9.3 (range = 3–21). There was no facility difference in age of the subjects (t(115) = 1.247, P = 0.22) or in the number of sedations the animal experienced during the past year (t(115) = 0.195, P = 0.85; Table 1). However, the number of days the animals were singly housed during the prior year was greater at Facility 1 (t(115) = 2.274, P < 0.05) while the number of location changes the animals experienced during the prior year was greater at Facility 2 (t(115) = −3.909, P < 0.001; Table 1).
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Correlations were conducted on the independent variables for each facility separately. At Facility 1, the number of location changes was negatively correlated with age (r = −0.346, P < 0.05) and days singly housed during the prior year (r = −0.346, P < 0.05). At Facility 2, females were older (r = 0.466, P < 0.001), had more sedations (r = 0.446, P < 0.001) and more location changes (r = 0.268, p < 0.05). In addition, the number of location changes was correlated with the number of days singly housed (r = 0.219, P < 0.05) and age (r = 0.222, P < 0.05).
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Alopecia
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At Facility 1, the subjects in the “high alopecia” group were missing hair from an average of 50.1% of their bodies (range: 16.4 – 85.8%) while the “low alopecia” group subjects were missing hair from an average of 0.32% of their bodies (range: 0–1.44%). At Facility 2, the subjects overall were missing hair from an average of 6.25% of their bodies (range: 0– 38.8%). Age, the number of days singly housed, and the age×number of days singly housed interaction contributed to alopecia expression at both facilities. No other predictors were significant (Table 2). Examination of the raw data and predicted model values revealed a crossover interaction between age and the number of days singly housed. As animals increased in age and days singly housed, the probability of having high levels of alopecia also increased (Figure 1).
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Hair Cortisol At Facility 1, hair cortisol levels averaged 77.7 ± 6.3 pg/mg. Sex and number of location changes contributed significantly to levels of hair cortisol, explaining a total of 44.4% of the variance. Females had higher levels of hair cortisol than males, and animals with more location changes had increased levels of hair cortisol. At Facility 2, the hair cortisol levels averaged 56.1 ± 2.4 pg/mg. The number of sedations was the only predictor of hair cortisol, explaining 28.5% of the variance; animals with more sedations had an increase in hair cortisol levels (Table 2). Relationship between Alopecia and Hair Cortisol
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At Facility 1, animals with high levels of alopecia had significantly higher levels of hair cortisol than did those with low levels of alopecia (98.6 ± 11.8 vs. 63.1 ± 4.8 pg/mg; t(32) = 3.118, p < 0.005), but there was no relationship between alopecia and hair cortisol at Facility 2 (r = −0.117, P = 0.292).
Discussion This study investigated alopecia and hair cortisol at two National Primate Research Centers. Because the subjects were not all randomly selected and because of the cross-center variability in the variables being studied, analyses were conducted separately for each facility and therefore do not indicate true differences in facility populations.
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At Facility 1, the “high alopecia group” had significantly higher levels of hair cortisol than the “low alopecia group”, demonstrating some evidence that alopecia may be associated with hair cortisol levels. However, there was no association at Facility 2, suggesting that alopecia is not a consistent marker of chronic stress as indicated by hair cortisol levels. These differential results are similar to those of Novak et al. (2014), which used some of the same subjects. The reason for this facility difference in association remains unclear and may be due to differences in research protocols, animal management practices (e.g., the number of days the animals were singly housed), or genetic differences in the two populations. Any given relationship between alopecia and cortisol, however, is not necessarily a causal
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relationship. Stress may result in hair loss, but alternatively, hair loss (and its potential effect on thermoregulation) may result in an increase in stress [30]. Hair loss and stress may have interacted differentially at the two facilities, resulting in different outcomes. Sex effect
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Overall, there was no significant effect of sex on alopecia. This result is in contrast to many previous studies on alopecia that report a significant sex difference, typically with more females than males showing hair loss [8, 21 22, 25, 38]. This sex difference has been attributed in part to pregnancy [4, 13]. Although some of the animals in the present study were recently removed from breeding groups, all were housed singly or in non-breeding pairs at the time of data collection, and it is unlikely that any females were pregnant at the time of sampling. Therefore, the lack of sex difference in alopecia may be due in part to an absence of pregnant females in the population. This result is not unique, however. For example, Crockett et al., (2007) also reported no sex difference in alopecia. Sex alone may therefore only play a minor role in the extent of alopecia.
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In contrast, there was a significant effect of sex on hair cortisol; however, this was only evident at Facility 1. Crockett et al. (1993) reported that female longtailed macaques tended to have higher cortisol values than males, especially in response to potentially stressful events such as room change, sedation, and tethering procedures, but the sex difference was reduced once the animals were habituated, suggesting that there may be instead a sex difference in reactivity. The reason for the differing results at the two facilities in the present study is unknown. There was no facility difference in number of sedations, and the subjects at Facility 1 actually had fewer room changes than those at Facility 2. Perhaps the females at Facility 1 were more reactive and/or more greatly affected by housing conditions or research protocols that were not assessed in the present study. Further research in this area needs to be conducted. Age and Single Housing effect
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In previous studies, alopecia has been reported to increase with age [4, 21, 31]; older animals tended to have greater amounts of alopecia and hair thinning than their younger counterparts [19, 31]. However, this relationship is not consistent across studies. For example, Luchins et al. (2011) reported no age effect, and Kroeker et al. (2014) reported that the oldest animals actually had a better coat than the younger adult subjects. In the present study, we found a significant age × number of days singly housed interaction at both facilities. As animals increased in age and the time they were singly housed, the probability of having high levels of alopecia or being in the “high alopecia” category also increased. This finding is perhaps more remarkable since information from only the past year of each animal’s social history was used in the analysis. This age effect may be related to factors such as hair-pulling or friction from cage contact. For example, in a study of singly housed rhesus monkeys, older animals were more likely than younger animals to pull out their own hair [26]. In addition, some patterns of alopecia have been reported to match cage mesh patterns and may be due to the friction caused by leaning against the cage sides [30]. This may be more likely to occur in singly housed and older animals, because they tend to be less active than their socially housed or younger counterparts [2, 34]. Therefore, although hair
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pulling, activity, and cage friction were not directly assessed in the present study, they may have been contributors to hair loss, especially in older animals. Number of Sedations
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The number of sedations during the prior year was not associated with alopecia at either facility. However, it was associated with an increase in hair cortisol at Facility 2. Sedation procedures generally involve capture and/or restraint, which alone can result in activation of the HPA axis. The disorientation that occurs before the animal is fully sedated as well as the temporary discomfort of the injection may also play a role [35]. For example, short-term stress from a single sedation via darting has been shown to increase serum cortisol in chimpanzees (Pan troglodytes) [1]. Sedation has also resulted in an increase in serum cortisol in baboons (Papio spp.) [5] and adult Cebus monkeys (Cebus apella) [23]. However, not all sedations resulted in an increase in cortisol [5, 27, 40]. In a study of adult male rhesus monkeys, cortisol increased in the animals that received three injections of ketamine over a period of two hours, but not in monkeys that received a single injection [33]. One factor that may play a role in different results may be whether the monkeys observed other animals undergo restraint and sedation. In male (but not female) rhesus monkeys there was a positive correlation between levels of plasma cortisol and the order in which they were sedated in a colony room. When the room was arranged so the animals could not see each other, this effect was not observed [15]. Perhaps the different results at the two facilities occurred because of differences in the timing or location of the procedures performed during sedation. In addition, the drugs utilized for sedation may also have played a role. For example, ketamine and Telazol were shown to have differential effects on plasma cortisol. In rhesus macaques, ketamine had little effect on cortisol, but Telazol was shown to reduce cortisol in morning samples [5]. Telazol was involved in 4.3% of the sedations at Facility 1, but only 0.4% of the sedations at Facility 2. Perhaps the type of drug utilized for sedation played some role in the differing results. The effect of sedation on cortisol is complex and may be influenced by a number of factors including sedation procedures, familiarity of the subjects with the procedures, drug type, dose, and time of day [5]. In addition, the reasons for sedation (routine colony maintenance, clinical or research needs, etc.) may themselves have contributed independently to hair cortisol levels. The complexity of and contrasting results in sedation effects on stress demonstrate the need for further study. Number of Location Changes
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The number of location changes during the prior year was not associated with alopecia, but it was associated with an increase in hair cortisol at Facility 1. The movement of an animal to a novel location has been used as a stressor in a number of studies [6, 7, 16]. Although the location changes in the present study were limited to within-facility moves, they included moves either to a different room or to a different building, for husbandry or research purposes. Such relocations included not only changes to the animal’s physical environment, but also to the social environment, as previous social partners are left behind while new social contacts are made. It is therefore not surprising that these moves are also associated with an increase in hair cortisol. The impact of location changes on stress has been reported in a number of cases, with stress increasing as measured both behaviorally and physiologically. Relocation can result in behavioral changes lasting days to weeks after the J Med Primatol. Author manuscript; available in PMC 2017 August 01.
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move [18, 29]. Whether the move is within a facility or between facilities, the impact on the HPA axis is also evident. For example, relocation to a new facility resulted in significantly higher levels of fecal cortisol in Garnett’s bushbabies (Otolemur garnettii) on the day of the move, which returned to baseline one week after the move [41]. Similarly, after moving to a new building within a facility, male rhesus monkeys had significantly elevated serum cortisol levels between one hour to seven days after the move [11, 32], and elevated hair cortisol 4 months post-move [11]. The reason for a difference in results between the two facilities in the present study is unclear. However, the number of location changes at Facility 1 was negatively correlated with age. The younger animals may have been more greatly impacted by the moves than were the older animals. In addition, the number of relocations was significantly greater at Facility 2. Perhaps because of this, each move at this facility had less of an effect on the animals. Some animals at this facility were also moved in groups rather than individually. This may have helped to modulate the stressfulness of relocation, as the presence of a familiar companion has been reported to reduce the stress response [43].
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Conclusion
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The results of this study demonstrate that alopecia is not an uncommon occurrence in populations of captive nonhuman primates and that it is related in part to stress as measured by hair cortisol. However, facility differences were evident in the association between alopecia and cortisol and in risk factors associated with these variables. Although potential contributing factors to these facility differences have not been identified, they may include differences in variables such as husbandry procedures, research protocols, or genetic makeup of the subjects. Both intrinsic and environmental risk factors contributed to levels of alopecia and hair cortisol, but their contributions differed; age and proportion of the year singly housed played significant roles in alopecia, while sex, number of sedations, and number of location changes had a greater impact on hair cortisol. Therefore, alopecia and hair cortisol may be impacted differentially by intrinsic and environmental variables. However, all variables should be considered when making decisions regarding animal management. For example, days singly housed, the number of sedations, and the number of location changes should be limited whenever possible.
Acknowledgments We would like to thank Brittany Peterson (SNPRC), Nicola D. Robertson (ONPRC), and Daniel Gottlieb (ONPRC) for assistance with data collection. This research was supported by grants R24OD01180-15 to Melinda Novak at the University of Massachusetts, P51OD011133 to Texas Biomedical Research Institute (SNPRC), P51OD010425 to WaNPRC, and P51OD011092 to ONPRC.
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Age × Days singly housed interaction for Facility 1 (top) and Facility 2 (bottom). For Facility 2, the alopecia groups (low vs. high) were based on a median split.
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Table 1
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Mean ± SE of each of the variables for the different facilities Variable
Facility 1
Facility 2
Age (Years)
10.1 ± 0.8
9.0 ± 0.4
Number of days singly housed during the prior year*
209.3 ± 24.5
148.9 ± 14.1
Number of sedations during the prior year
6.9 ± 0.7
6.7 ± 0.6
Number of location changes during the prior year*
1.5 ± 0.3
3.9 ± 0.4
*
Significant Facility differences
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Facility 2
Facility 1
b = 28.576 P < 0.01
Hair Cortisol
Facility 2
Facility 1
Alopecia
Sex
b = −1.093 P < 0.005
b = −0.201 P = 0.234
Age
b = −0.054 P < 0.005
b = −0.022 P < 0.05
Number of Days Singly Housed
b = 2.060 P < 0.001
Number of Sedations
b = 6.688 P < 0.05
Number of Location Changes
b = 0.004 P < 0.05
b = 0.002 P < 0.05
Days Singly Housed × Age
Beta values and associated significance levels for terms included in best fit models
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Table 2 Lutz et al. Page 15
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