Abstract

Contraception is commonly used to manage captive breeding programs. Yet, like any other pharmaceutical, contraceptives are not without risk. In order to define and characterize such risks, contraception is evaluated by comparing the occurrence of adverse reactions in contracepted animals to those occurring in control animals. Because zoo species are usually not included among those for which the label is approved, similar to most of the drugs used by zoo veterinarians, contraceptives are used off-label and efficacy and safety information are gathered while they are being used. Veterinarians rely on this type of information to oversee the health of each individual, but in the case of reproductive health, the species will also benefit.

Since its inception by Dr. Linda Munson, the Contraceptive Health Surveillance Program has played an important role in documenting adverse effects of contraceptives such as melengestrol acetate (MGA) through gross pathology and histopathology. Examples of this are the increased risk of endometrial hyperplasia and mineralization in felids and canids with MGA exposure, the risk of mammary adenocarcinomas in MGA-treated animals,^5,8,9 and the inflammatory response in felids to pZP vaccination.⁶ The program has also played a key role in documenting that certain conditions are not associated with contraceptive use, such as leiomyomas in felids,³ ovarian lesions in felids and canids,^7,8 and cystic endometrial hyperplasia in elephants.¹ Currently the effects of deslorelin in canids are being evaluated in collaboration with the Wildlife Contraception Center and Species Survival Plans.^4,10

Historically, contracepted animals have been compared to non-contracepted as controls; however, more recently it has become clear that there is a difference between non-contracepted parous and non-contracepted nulliparous animals.² Non-contracepted females that are housed alone may be exposed to repeated infertile cycles and concomitant endogenous hormones. The time since the last parturition (number of barren cycles) may be a risk factor for certain lesions.

Presently, the Contraceptive Health Surveillance Project tissue archive contains more than 2000 reproductive tracts. Most of them are female, but as newer methods are used such as deslorelin in males, it becomes even more important to continue to contribute to this archive. In spite of the large number of cases, there are some species which are poorly represented, for example hyenas, rodents (porcupines and beavers), small carnivores, and bears. These findings and the ability of the Reproductive Health Surveillance Program to provide information on adverse effects and normal aging pathology of the reproductive tract are possible, thanks to the veterinarians who have submitted the reproductive tracts of contraceptive-treated and non-treated animals along with their complete reproductive histories.

Literature Cited

1.  Agnew, DW, L Munson, EC Ramsey. 2004. Cystic endometrial hyperplasia in elephants. Vet. Pathol. 41: 179–183.

2.  Asa, CS, L Penfold, D Powell, and K Traylor-Holzer, K. 2011. AZA session “Use it or lose it” Annual conference Atlanta, September, 2011.

3.  Chassy, LM, IA Gardner, ED Plotka, L Munson. 2002. Genital tract smooth muscle tumors are common in zoo felids but are not associated with melengestrol acetate contraceptive treatment. Vet. Pathol. 39: 379–385.

4.  Devery S. 2010. A retrospective study of pyometra and endometrial hyperplasia in captive African wild dogs (Lycaon pictus), bush dogs (Speothos venaticus) and fennec foxes (Vulpes zerda) in North America. MSc Thesis, University of London.

5.  Harrenstien LA, Munson L, Seal US, American Zoo Aquarium Association Mammary Cancer Study Group. 1996. Mammary cancer in captive wild felids and risk factors for its development: a retrospective study of the clinical behavior of 31 cases. J Zoo Wildl Med 27:468–476.

6.  Harrenstien LA, Munson L, Chassy LM, Liu IK, Kirkpatrick JF. 2004. Effects of porcine zona pellucida immunocontraceptives in zoo felids. J Zoo Wildl Med. 35:271–9.

7.  Kazensky CA, Munson L, Seal US. 1998. The effects of melengestrol acetate on the ovaries of captive wild felids. J Zoo Wildl Med. 29:1–5.

8.  Moresco A, L Munson, IA Gardner. 2009. Naturally occurring and melengestrol acetate associated reproductive tract lesions in zoo canids. Vet. Pathol. 46: 1117–1128.

9.  Munson L, Gardner IA, Mason RJ, Chassy LM, Seal US. 2002. Endometrial hyperplasia and mineralization in zoo felids treated with melengestrol acetate contraceptives. Vet Pathol 39:419–427.

10.  Zordan, M. 2012. Occurrence of endometrial hyperplasia, hydrometra and pyometra in four species of captive canids with seasonal reproduction. Doctor of Veterinary Medicine Thesis. Veterinary Sciences, University of Chile.