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Research Papers

These studies could not have been conducted without generous assistance from Kh. Sompast Meepan.  He provided advice on bull behavior, as well as giving guidance to mahouts on elephant handling for sampling, particularly when bulls were in musth. Access to Kh. Sompast's uniquely large population of tractable adult bulls, along with the participation of well-trained and extremely supportive mahouts, in combination with Kh. Sompast's vast knowledge of elephant behavior, enabled this work to take place.                        Lisa Yon

“A longitudinal study of LH, gonadal and adrenal steroids in four intact Asian bull elephants (Elephas maximus) and one castrate African bull (Loxodonta africana) during musth and non-musth periods”

During musth, a number of hormones in the body are increased. Until now, the only hormones studied have been the male sex hormones, testosterone, androstenedione and dihydrotestosterone. All of these hormones are produced by the testes in the bull elephant.

Musth can be seen as a very stressful time for a bull elephant. Bulls in musth decrease their food intake, greatly increase their territories (so they roam over a much larger range), fight more with other elephants (and with other species), and at the height of musth they lose large amounts of water to urine dribbling (they become 'incontinent' and dribble urine almost constantly; this is probably to leave specific chemicals behind to communicate their state to other elephants). The adrenal glands are involved in the stress response in most species studied to date, and it is reasonable to think that they would be active during the stressful time of musth.

The adrenal glands produce the hormone cortisol in times of stress, but they can also produce some sex hormones, including testosterone, androstenedione and the weaker male sex hormones (androgens) androstenediol and DHEA.  These last two hormones are produced in large part by the adrenal glands, not by the testes. The purpose of this study was to determine if the adrenal glands increase their hormone production during musth. Weekly blood samples were taken from two adult Asian bull elephants at the Ayutthaya Elephant Palace and Royal Kraal, and from two Asian bull elephants at the Oregon Zoo in the United States over a period of 11-15 months, during musth and non-musth periods. Samples were measured for levels of cortisol, testosterone, dihydrotestosterone, DHEA, androstenedione and androstenediol. In three of the four bulls, all of the hormones studied increased during musth, including those mostly produced by the adrenal glands. This suggests that the adrenal glands are actively producing hormones during musth in the Asian bull elephant. The significance of this adrenal hormone production is unknown.

“ACTH stimulation in four Asian bull elephants (Elephas maximus): An investigation of androgen sources in bull elephants”

This study was conducted to further explore the role of the adrenal glands in musth. The classical pathway for activating the adrenal glands in times of stress involves production and release of the hormone ACTH (adrenocorticotropic hormone) from the pituitary gland in the brain. This hormone then stimulates the adrenal glands to produce cortisol (a stress hormone), as well as some sex steroids (as mentioned above).

Synthetic ACTH was given to four adult Asian bull elephants at the Ayutthaya Elephant Palace and Royal Kraal. Blood samples were taken and measured for levels of cortisol and the male sex hormones (androgens) mentioned above (testosterone, androstenedione, androstenediol, and DHEA). Cortisol increased as expected in response to ACTH. The response of the androgens to the ACTH was quite different from the pattern seen during musth: DHEA doubled, androstenedione and androstenediol showed no consistent pattern of response, and testosterone actually decreased in all the bulls. During musth, by contrast, all of these hormones increased (testosterone markedly so). This pattern of results suggests that the classical adrenal gland activation pathway, which is triggered by stress, is not the route which is stimulating hormone production by the adrenal glands during musth.

Lisa Yon, BSc, DVM, PhD, MRCVS
Lecturer in Zoo and Wildlife Medicine
School of Veterinary Medicine and Science University of Nottingham,
Sutton Bonington

Head of Research
Twycross Zoo - East Midlands Zoological Society

University of Nottingham :
Tel. +44 (0) 115 951 6358
Fax +44 (0) 115 951 6440
email: lisa.yon@nottingham.ac.uk

Twycross Zoo:
Tel. +44 (0) 182 788 3136
email: lisa.yon@twycrosszoo.org

 







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