Recognizing the Impact of Environmental Stressors on Corticoid Levels in Captive Giant Pandas
Institutions that hold populations of captive species in hopes of breeding them must consider the impacts of physiologic stress on reproductive status. Physiologic stress can be measured in an individual by assessing levels of corticoids.1-4 Measuring physiologic stress is particularly important when the populations are endangered and have a poor track record for captive propagation. Pinpointing the potential source of stress and subsequent elevation of stress is of primary importance and needs to be considered from a variety of sources.
The aim of this study was to characterize the urinary cortisol response to environmental stressors, behavior, and health care management and to also investigate the relationship between stressor and behavioral expression of stress in giant pandas (Ailuropoda melanoleuca). We considered potential stressors from environmental sources (ambient noise); husbandry and veterinary requirements (including anesthesia), and the health of the animal in question. To further evaluate the impact of these stressors on the physiologic condition of the animals, we also looked at the correlation between behavioral stress and elevated cortisol levels.
The current study reflects data gathered primarily from two giant pandas (a 20-yr-old wild caught male, and a 7-yr-old captive bred female) housed at the San Diego Zoo (SDZ). Additional hormonal data were collected at the Giant Panda Breeding Center in Wolong China. Behavioral data was collected at the SDZ for 2 hr, twice daily, 5 days/wk. Activity budgets were determined using scan sampling, at 1-min intervals. The ethogram contains over 100 behaviors related to feeding, locomotion, stress, courtship/social interactions, stereotypies, etc. Stress behaviors include the following: pacing, door-directed behavior, and scratching. Ambient noise levels were recorded continuously using a Cel Instruments 573 sound meter. Urine samples, when possible, were collected daily, during the period of September 1996 through April 1999 at SDZ and between April 1997 through July 1997 at Wolong. Samples were kept frozen at -20°C until analysis. Urinary cortisol levels were determined by radioimmunoassay as previously described.4 Duplicate 10 µl aliquots from each urine sample were directly analyzed using cortisol antibody (Lot #R2-P, ICN Biomedicals Inc., Costa Mesa, California). Cross-reactivity was 100% with cortisol, 11.4% with 21-desoxycorticosterone, 8.9% with 11-desoxycortisol, 1.6% with corticosterone and <1% with other urinary metabolites. Detection limits were 7.8 to 1000 pg/tube. Variation in urine concentration were corrected relative to creatinine (Cr) concentration. Samples with Cr value <0.05 mg Cr/ml were not used.
In this preliminary study, mean basal urinary cortisol concentrations ranged from 50 ng/mg Cr (at Wolong) to 100 ng/mg Cr (at SDZ). There was a 5–10 fold increase in cortisol levels following routine health exams (650–1,335 ng/mg Cr), artificial insemination (647 ng/mg Cr), and initial medical treatment for epistaxis with propanolol (elevated levels returned to baseline 2 days following treatment). Elevated cortisol levels (200–600 ng/mg Cr) were occasionally noted following the occurrence of mucous stools. Additionally, preliminary analysis of the relationship between ambient noise levels (decibels) and cortisol levels in the San Diego female have shown a positive interaction between the two (Mann-Whitney U: z=-2.75; n=30; p=0.006). There was also a positive correlation between the percent time spent engaged in stress related behaviors and cortisol levels (elevated cortisol: 3.76±1.02 SE; Normal cortisol: 1.76±0.42 SE), but this correlation was not significant (Mann-Whitney R: z=-1.41; n1=53; n2=61; p=0.15). Correlation between behavioral stress and ambient noise level was also positive. But weak (Low db: 4.17±2.06 SE; High dB: 5.12±1.52 SE). This correlation was not significant (Mann-Whitney U: z=-1.19; n=30; p=0.23).
1. Carlstead K, JL Brown, SL Monfort, R Killens, DE Wildt. 1992. Urinary monitoring of adrenal responses to physiological stressors in domestic and nondomestic felids. Zoo Biology. 11:165–176.
2. Czekala NM, VA Lance, M Sutherland-Smith. 1994. Diurnal corticoids excretion in the human and gorilla. Am J Primatology. 4:29–34.
3. Monfort SL, KL Mashburn, BA Brewer, SR Creel. 1998. Evaluating adrenal activity in African wild dogs (Lycon pictus) by fecal corticosteroid analysis. J. Zoo and Wildl. Med. 29(2):129–133.
4. Robbins MM, NM Czekala. 1997. A preliminary investigation of urinary testosterone and cortisol levels in wild male mountain gorillas. Am J Primatology. 43:51–64.