Abstract

Many species, including canids, are effectively contracepted with progestins, and melengestrol acetate (MGA) has been widely used for zoo species. Chronic use of progestins has been associated with significant gynecologic lesions in felids. This project investigates whether progestin contraceptives also affect reproductive health in canids by comparing uterine lesions in MGA-treated and untreated (control) zoo canids. Reproductive tracts from adult canids at United States zoos were obtained from submissions to the Association of Zoos & Aquariums Wildlife Contraception Center Health Surveillance Program. Reproductive tracts were sampled following standard protocols and processed routinely for histopathology. Microscopic evaluations were performed without knowledge of treatment. Ovaries were examined for tertiary follicles or corpora lutea and uteri were evaluated for endometrial hyperplasia (EH), metritis, pyometra, hydrometra, mineralization, endometrial atrophy, and adenomyosis. Lesion prevalence was compared between treated and control groups, controlling for age and parity. Ninety-one cases (68 controls and 23 treated) representing 13 species were included. Advanced EH, hydrometra, and mineralization were more prevalent in treated than control groups (39% vs. 9%; 70% vs. 22%; 52% vs. 0% resp). An additional 47% of treated animals (vs. 3% controls) had such severe hydrometra or pyometra that EH could not be graded. Endometrial hyperplasia, mineralization, and hydrometra were associated with MGA exposure. Because these lesions can permanently impair the fertility of females, long-term use of MGA for contraception of genetically valuable canids is not recommended.

Acknowledgments

The authors thank all participating institutions, as well as the veterinarians, curators, technicians, and registrars that have sent reproductive tracts as well as the information necessary to include the cases in this study. This project was partially funded by the Association of Zoos and Aquariums Conservation Endowment Fund.