Naturally occurring and melengestrol acetate-associated reproductive tract lesions in zoo canids

Vet Pathol. 2009 Nov;46(6):1117-28. doi: 10.1354/vp.08-VP-0293-M-FL. Epub 2009 Jul 15.


As husbandry practices have improved, safe and effective contraception for captive wildlife management has become a necessity. Melengestrol acetate (MGA), a synthetic progestin, is highly effective and has been used in many zoo species. Long-term use of MGA has been associated with uterine lesions in zoo felids, but effects in zoo canids have not been evaluated. This retrospective study documented spontaneously occurring lesions and investigated the impact of MGA on the reproductive health of zoo canids. Reproductive tracts from adult females were submitted by US zoos to the Association of Zoos & Aquariums' Wildlife Contraception Center Health Surveillance Program. Reproductive tracts were sampled and processed for histopathologic examination following standard protocols. Microscopic evaluations were performed without prior knowledge of MGA treatment status. Prevalence of uterine lesions was evaluated and compared between MGA-treated animals (n = 20) and control (untreated) animals (n = 61). Common lesions within the study population as a whole included endometrial hyperplasia (predominantly cystic) (53%), hydrometra (33%), and adenomyosis (25%). Treatment with MGA was a risk factor for endometrial hyperplasia, hydrometra, fibrosis, and adenomyosis. Uterine mineralization occurred exclusively in MGA-treated animals. Results indicate that MGA contraception can lead to lesions that may permanently impair the fertility of females. Therefore, if long-term contraception of zoo canids is necessary, the use of alternate methods of reproductive control such as gonadotropin-releasing hormone (GnRH) analogs or GnRH vaccines that reduce gonadal hormone exposure should be pursued.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Animals, Zoo
  • Canidae*
  • Contraceptive Agents, Female / adverse effects*
  • Female
  • Melengestrol Acetate / adverse effects*
  • Odds Ratio
  • Ovarian Diseases / chemically induced
  • Ovarian Diseases / pathology
  • Ovarian Diseases / veterinary*
  • Risk Factors
  • Uterine Diseases / chemically induced
  • Uterine Diseases / pathology
  • Uterine Diseases / veterinary*


  • Contraceptive Agents, Female
  • Melengestrol Acetate