A Comparative Study of Blood Lipids and Stress Levels Between Captive and Semi-Captive Orangutans (Pongo pygmaeus) Under Tropical Conditions
American Association of Zoo Veterinarians Conference 2007
Choy Foon Seng; Goh Yong Meng, DVM, PhD; Rasedee Abdullah, MSc, PhD
Faculty of Veterinary Medicine, Universiti Putra Malaysia, Selangor Darul Ehsan, Malaysia


Blood samples were collected from 27 orangutans (Pongo pygmaeus) (14 captive and 13 semi-captive) and were analyzed for triglycerides, total cholesterol, high density lipoprotein cholesterol (HDLC), low density lipoprotein cholesterol (LDLC), glucose, cortisol levels, total red blood cells (RBC), white blood cells (WBC), and WBC differential count. There were significant differences (p<0.05) in total cholesterol and HDLC level between groups where semi-captive males had the highest level while the lowest were the captive male orangutans. When the blood lipid values were compared across age groups, the triglyceride, total cholesterol, and HDLC levels of adult animals differ significantly (p<0.05) from the younger age groups. Finally, captive orangutans had higher (p<0.05) serum cortisol level and N:L ratio as compared to semi-captive orangutans suggesting that captive orangutans are in more stressful states. Based on the results, captive orangutans tend to have “less” desirable blood lipids and are “potentially” more stressed than semi-captive orangutans. In this study, it is evident that nutrition plays a sizable role in determining the blood lipid levels. Other factors that affect blood lipids are gender and age. It was postulated that the lack of stimulating environment and enrichment programs in captive environment, may have led to the increase in stress indicators.


The major challenge that is faced by keeping any animal in captivity would be to simulate a diet and habitat that is as natural as possible. However, limited knowledge of the physiology and natural diet of the orangutan has led to the feeding of a diet that is quantitatively and qualitatively different from their natural diet.8 Many captive orangutans had been fed an urbanized diet that is typically high in fat and carbohydrate.9 Captive orangutans may also be subjected to an unenriched and non-stimulating environment that may result in stressful states. Consequently, many captive orangutans end up being overweight and suffer from excessive boredom. Obesity, hypercholestremia, HDLC/ LDLC imbalance, and chronic stress are among the risk factors for atherosclerosis, coronary heart disease, hypertension, diabetes mellitus, and myocardial infarction that have been identified in human populations.10 However, these risk factors have never been studied or identified in orangutans. Therefore, this study was conducted to assess and compare the blood lipid profile and stress levels of captive and semi-captive orangutans as well as to contribute towards the database for blood lipids and stress levels in captive orangutans kept under tropical conditions.

Materials and Methods

Animals and Blood Collection

A total of 27 Bornean orangutans (Pongo pygmaeus) of various sex and age were included in this study where 14 animals were sampled from captive location (National Zoo of Malaysia & Sabah Zoological and Botanical Garden, Malaysia) while 13 animals from a semi-captive location (Sepilok Orangutan Rehabilitation Center, Malaysia). General anaesthesia was induced by using tiletamine and zolazepam/ Zoletil 100® (Virbac Laboratories, NSW, Australia) at the dosage of 3–5 mg/kg intramuscularly via hand syringe, blowpipe, or air-pressured pistols. Following immobilization, a physical examination was performed to ensure the good health of the animal. 10 ml of blood were collected from either the brachial, cephalic, or femoral vein and 3 ml of blood are placed in EDTA (Vacutainer® K2 EDTA, Becton-Dickinson & Co, Franklin Lakes, NJ, USA) and the remaining in serum separator tubes (SST™, Becton-Dickinson & Co, Franklin Lakes, NJ, USA), stored in 4°C and processed within 24 hours. Serum was obtained after centrifuging the blood samples at 5000 G for 5 minutes. The serum samples were kept at -20°C in 1.5 ml microcentrifuge tubes (Eppendorf®, Hamburg, Germany) for subsequent serum biochemistry and cortisol assay.

Hematology and Serum Biochemistry

Total white blood cells (WBC) were manually quantified using the hemocytometer techniques. Thin blood films were also made, air dried and stained with Wright’s stain (Sigma®, Sigma-Aldrich Corporation, MO, USA). WBC differential count was performed after Wright staining. The neutrophil: lymphocyte (N:L) ratio was calculated from the differential counts. Serum biochemistry results were obtained by processing the thawed frozen serum on an automated analyzer (Hitachi® 902, Roche Diagnostics, GmBH, Germany). The parameters that were analyzed included total cholesterol, triglyceride, high density lipoprotein cholesterol (HDLC), and low-density lipoprotein cholesterol (LDLC), sodium, potassium, chloride, calcium, and phosphate. Serum cortisol was measured using a cortisol test kit (Coat-A-Count®, Diagnostic Product Corporation, Los Angeles, CA, USA). Glucose was measured using a portable glucometer immediately after the blood samples were collected.


Differences in blood lipid values were compared across management status, gender, and ages using one way ANOVA procedure meanwhile differences in stress indicators were compared using two tailed t-test. Significant different means were then elucidated using Duncan’s New Multiple Range test. All statistical analyses were performed using SPSS version 14.0 at 95% confidence level.



The blood lipid values of orangutans segregated according to management system and sex are shown in Table 1. There were significant differences (p<0.05) in total cholesterol and HDLC levels between groups where semi-captive males had the highest level while the lowest was in the captive male orangutans. When the blood lipid values were compared across age groups, the triglyceride was found to be significantly higher (p<0.05) while the total cholesterol and HDLC levels were significantly lower (p<0.05) in adult orangutans. In fact, there was a strong correlation of triglyceride with the age of the animal (Pearson’s correlation = 0.493, p=0.009). A trend was seen in the blood lipid profiles in male and female orangutans. Male orangutans had higher levels of triglyceride, total cholesterol, LDLC, and Chol/HDLC ratio compared to female orangutans. These results will be compared to the ISIS normal ranges.5

Table 1. Blood lipid values of orangutans based on management system and sex (values expressed as mean ± SEM)




Blood lipid values










Total Cholesterol




















Chol/HDLC ratio





a,bMeans in the same row with different superscripts are significantly different (p<0.05)

Stress Levels

Captive orangutans had significantly higher (p<0.05) levels of serum cortisol and neutrophil:lymphocyte ratio (N:L ratio) as compared to semi-captive orangutans (Table 2). The serum cortisol level of captive orangutans was almost two times higher than semi-captive specimens. However, there were no differences in glucose and cholesterol levels. These results will be compared to the ISIS normal ranges.5

Table 2. Stress indicators of orangutans based on management system (values expressed as mean ± SEM)

Stress indicators



Serum Cortisol



Neutrophil: Lymphocyte ratio









a,bMeans in the same row with different superscripts are significantly different (p<0.05).



The differences in the lipid profile of the captive and semi-captive orangutans could be mainly due to the differences in nutritional management. One of the captive locations feeds the animal with high carbohydrate and triglyceride food items such as coconut, cocoa bread, milk, and sugar cane. Carbohydrates tend to raise serum triglyceride and decrease LDLC levels especially if it comprises at least 60% of the total calories.4 The cocoa bread and milk contains butter and milk fat which can potentially elevate the triglyceride and cholesterol levels. Furthermore, coconut is a major source of myristic and lauric acid, both potent cholesterol-raising fatty acids.3 Meanwhile, only bananas and milk are offered as a supplementary feed only in the semi-captive location. The amounts offered were designed not to fulfill daily caloric requirements. This would promote more foraging activities and help in achieving the objectives of the rehabilitation program.

Semi-captive orangutans have an easier access to food items that are high in dietary and structural fibers. There is a strong inverse correlation between dietary fiber and coronary heart disease. Soluble fibers such as β-glucan (found in oats, barley, and yeast), psyllium (found in husks of blonde psyllium seed), and pectin (found in fruits) have been demonstrated to effectively lower blood cholesterol levels.4 When compared across age groups, older orangutans have higher triglycerides, LDLC and Chol/HDLC ratio and lower HDLC/LDLC ratio. It is believed that the age of the patient reflects the cumulative exposure to atherogenic risk factors throughout its life.10

Stress Levels

Responses to stressors often involve changes in physiologic function (biochemical, neuroendocrine, metabolic), immunity, reproductive, histopathology, psychologic state, behaviour, and toxicology status.1,6 In this study, only endocrine (cortisol), immunology (N:L ratio), and to a certain extent, metabolic (glucose and cholesterol) and behavioural parameters were measured and evaluated. However, behavioural changes were only subjectively accessed by comparing the natural behaviour between semi-captive and captive orangutans and, therefore, were not conclusive in this study. One of the factors that could have elevated the stress indicators in captive orangutans is the lack of stimulating environment and activities. By nature, the orangutan’s feet are adapted to life in the tree than on the ground.2 Many zoo managements fail to provide the orangutans with sufficient vertical space and structures that allow arboreal locomotion. Besides that, captivity has removed much of the complexity and seasonality of food sources. Without understanding the importance of seasonal availability of food in the feeding ecology of an animal, captive animals are typically fed discrete meals at predictable times, year in and year out.7 In this study, the influence of the diet that differs dramatically from their natural diet in terms of quantity and quality on the stress levels of the animals has yet to be investigated.


In conclusion, captive orangutans had “less” desirable blood lipids and are “potentially” more stressed than semi-captive orangutans. In this study, is evident that nutrition plays a sizable role in determining the blood lipids. Other factors that affect blood lipids are gender and age. As for the stress levels, it was postulated that the lack of stimulating environments and the limited enrichment programs may have led to the increased stress indicators seen among captive orangutans in this study.

Literature Cited

1.  Balm PH. Preface. In: Balm PH, eds. Stress Physiology in Animals. Sheffield, England: Sheffield Academic Press; 1999.

2.  Benneth EL. The Natural History of Orang-utan, 2nd ed. (Borneo) Malaysia: Natural History Publication; 2002.

3.  Grundy SM, Denke MA. Dietary influences on serum lipids and lipoproteins. J Lipid Res. 1990;31:1149–1172.

4.  Hilpert KF, Griel AE, Psota T, Gebauer S, Coa Y, Kris-Etherton PM. New insights on the role of lipids and lipoproteins. In: Moffatt RJ, Stamford B, eds. Lipid Metabolism and Health, 1st ed. London, England: CRC Press; 2006:211–264.

5.  International Species Information System. 2002. Physiological Reference Value for Pongo pygmaeus. International Species Information System, Apple Valley, MN.

6.  National Research Council. Recognition and Alleviation of Pain and Distress in Laboratory Animals. Washington, DC: National Academy Press; 1992.

7.  Oftedal OT, Allen ME. Nutrition and dietary evaluation in zoos. In: Kleiman DG, Allen ME, Thompson KV, Lumpkin S, eds. Wild Mammals in Captivity: Principles and Techniques, 1st ed. Chicago, IL: The University of Chicago Press; 1996:109–128.

8.  Robbins CT. Wildlife Feeding and Nutrition, 2nd ed. New York, NY: Academic Press; 1993.

9.  Schmidt D. Nutrition. Orangutan Husbandry Manual. Brookfield, IL: Chicago Zoological Society; 2004.

10.  Third Report of the National Cholesterol Education Program. Expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III). Circulation. 2002;106:3143–3422.


Speaker Information
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Choy Foon Seng
Universiti Putra Malaysia
Serdang, Selangor Darul Ehsan, Malaysia

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