Effects of a GnRH Vaccine on the Estrous Cycle of an Asian Elephant (Elephas maximus)
American Association of Zoo Veterinarians Conference 2009
Nancy C. Boedeker1, DVM; Suzan Murray1, DVM, DACZM; David M. de Avila2; Janine L. Brown1, PhD
1National Zoological Park, Smithsonian Institution, Washington, DC, USA; 2Department of Animal Sciences, Washington State University, Pullman, WA, USA


Repro-BLOC® gonadotropin-releasing hormone (GnRH) vaccine (Amplicon Vaccine LLC, Pullman, WA) is effective at suppressing estrous cyclicity in heifers.3,8 The production of antibodies to a GnRH fusion protein neutralizes GnRH, thereby preventing follicle-stimulating hormone and luteinizing hormone (LH) release from the anterior pituitary, leading to sterility in both genders. GnRH vaccines have been evaluated as a management tool in horses, ruminants, cervids, swine, dogs, and cats.2,5-7,9 GnRH vaccination has been used in male African4 and Asian (Thomas Hildebrandt, personal communication) elephants to decrease aggression.

Repro-BLOC® was administered to a geriatric female Asian elephant for management of suspected uterine leiomyomas associated with anemia and hemorrhage, although leiomyomas are not uncommon in this species and typically benign.1 We speculated that GnRH vaccination would be effective at suppressing ovarian activity in female elephants and would thereby reduce the size of the leiomyomas and minimize the risk of further hemorrhage. Five vaccinations in increasing doses from 3 to 30 mg were administered over 20 months before efficacy was documented. Serial serum analyses showed estrous cycle suppression in association with a rise in GnRH antibody binding and a decrease in progesterone and LH. Ultrasonographic examinations were performed to evaluate uterine changes. The hematocrit normalized soon after the initial hemorrhage with no recurrence of anemia. To the authors’ knowledge, this is the first reported use of a GnRH vaccine in a female elephant. GnRH vaccination in elephants shows great potential for reversible contraception and management of uterine pathology in older females and warrants further investigation.


We would like to thank Drs. Jerry Reeves, Valeria Conforti, Dennis Schmitt, and Thomas Hildebrandt, as well as the National Zoo’s elephant keeper and curatorial staff for their invaluable assistance with this case. We would also like to thank Amplicon Vaccine for their generous donation of the Repro-BLOC® vaccine and for covering the costs of GnRH titer analysis.

Literature Cited

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2.  Botha AE, Schulman ML, Bertschinger HJ, Guthrie AJ, Annandale CH, Hughes SB. The use of a GnRH vaccine to suppress mare ovarian activity in a large group of mares under field conditions. Wildl Res. 2008;35:548–554.

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5.  Dowsett KF, Pattie WA, Knott LM, Jackson AE, Hoskinson RM, Rigby RP, Moss BA. A preliminary study of immunological castration in colts. J Reprod Fertil Suppl. 1991;44:183–190.

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8.  Stevens JD, Sosa JM, De Avila DM, Oatley JM, Bertrand KP, Gaskins CT, Reeves JJ. Luteinizing hormone-releasing hormone fusion protein vaccines block estrous cycle activity in beef heifers. J Anim Sci. 2005;83:152–159.

9.  Turkstra J, Meloen R. Active immunization against gonadotropin-releasing hormone, an active tool to block the fertility axis in mammals. Accessed 2006. http://www.vetscite.org/publish/articles/000062/article.html. (VIN editor: link was not accessible as of 1/6/2021.)


Speaker Information
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Nancy C. Boedeker, DVM
National Zoological Park
Smithsonian Institution
Washington, DC, USA

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