Assessment of Cortisol Hormone Levels among Captive Gorilla Using Saliva and Urine Cortisol

Mountain gorillas (Gorilla berengei berengei) and Lowland gorillas (Gorilla berengei graueri) are the world's most endangered ape species. Both species have experienced poaching of adults and illegal trade. Confiscation of infants from illegal holders resulted in gorillas being kept in captivity at Kinigi in Rwanda, thus changing their natural environment. In captivity, gorillas have to cope with changes as a result of the design of enclosure, changes in food presentation, and social structures. Cortisol concentrations may rise in situation of stress and could be used as an indicator of an animal’s welfare. This study examined cortisol levels by quantifying cortisol in saliva and urine among captive gorillas at Kinigi. Saliva and urine samples were collected from eight orphan gorillas in the quarantine facility at Kinigi. The orphans were composed of six female and two males, aged between 4-8 years. Saliva samples were collected by swabbing the mouth with cotton swabs. Urine samples were collected from the ground or leaves using a syringe, immediately after urination. A total of ten urine and eight saliva samples were collected from each gorilla in the morning and evening and analysed using competitive ELISA. There was a significantly higher (p=0.001) saliva cortisol levels in female than male in the morning, meanwhile there was no significant difference (p=0.05) between female and male saliva cortisol levels in the evening samples. There was also a significantly higher (p=0.036) urine cortisol levels in the male than female in the morning, while there was no significant difference (p=0.05) between female and male urine cortisol levels in the evening. In conclusion female saliva cortisol was significantly higher in the morning and declined in the evening, and for male cortisol was low in the morning and significantly higher in the evening. For urine cortisol both male and female cortisol levels were high in morning and declined in the evening. No correlation between the urine and saliva samples in all samples collected in both morning and evening.