Elephant immunocontraception: evaluation of a GnRH immunological for the management of reproductive pathology in Asian elephants (Elephas maximus)

Many aging female elephants develop uterine pathologies (cystic endometrial hyperplasia, leiomyomas). Though often benign, these lesions can be associated with bloody discharge, colic, anemia, and decreased fertility.... [ view full abstract ]

Many aging female elephants develop uterine pathologies (cystic endometrial hyperplasia, leiomyomas). Though often benign, these lesions can be associated with bloody discharge, colic, anemia, and decreased fertility. Increased reproductive cycles and hormone exposure experienced by captive compared to wild elephants may be important factors in development of these pathologies. GnRH immunologicals stimulate anti-GnRH antibody production that blocks binding of GnRH to receptors, thereby inhibiting release of FSH and LH and halting ovarian steroidogenic activity and reproductive cyclicity. We hypothesized that cessation of elephant ovarian cyclicity through GnRH immunization would decrease the progression and negative impacts of reproductive tract pathologies by decreasing uterine size and vascularity. Ten non-breeding female elephants diagnosed with reproductive tract pathologies each received a GnRH immunological injection (Improvest®, Zoetis, Kalamazoo, MI), repeated up to 3 times, to determine time to effect and reversibility. They were monitored by pre- and post-immunization rectal ultrasound evaluation of reproductive pathologies, weekly serum progesterone levels and GnRH antibody titers, and monthly CBCs, blood chemistries and urinalyses. All but one elephant developed titers and progesterone remained at baseline for 2 to 9 months following an initial series of 3 or 4 Improvest® injections. After cycling resumed, 5 elephants were boostered with 2 or 3 injections, inducing and maintaining baseline progesterone levels for 2 to >24 months. Reproductive tract pathologies did not progress and in some cases appeared to regress post-immunization. Side effects were limited to localized injection site reactions. In this study, immunization with Improvest® appeared safe and effective in female Asian elephants. Time to effect and duration of effect are variable after the initial series; booster injections tend to have a more rapid, longer lasting effect. In addition to managing reproductive pathologies, there is potential for use of GnRH immunization for contraception where suitable elephant habitat to sustain large populations is limited.