Weighing the options for limiting surplus animals
Abstract
The unsustainability of many animal programs managed by zoos and aquariums has brought renewed attention to unresolved questions about various management strategies. Solving the "sustainability crisis" for many species will require housing more adults and producing more offspring than there are existing spaces in accredited zoos and aquariums. Careful reproductive management is central to addressing this challenge, but opinions differ about which management strategies are best for an individual, for a species, for an institution, or for a country or region. The primary options for limiting the number of animals that would be surplus to the population are to prevent reproduction or to euthanize. However, there is much misunderstanding about methods for controlling reproduction, in particular about contraceptives and species differences in their effects. Careful weighing of all the options is called for. Lifetime Reproductive Planning may help increase breeding success through careful reproductive management but cannot eliminate production of surplus animals. Limiting reproduction does not address the problem of animals already in the population. Despite best efforts and planning, consistently hitting target numbers for a population may never be achieved. Increasing capacity provides a temporary patch when targets are exceeded, but is not a long-term solution, since each generation potentially produces even more individuals needing even more space. Welfare considerations should…
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Due to population size constraints and logistical, financial, and practical challenges related to translocations, many healthy, fertile animals may never reproduce, even for highly endangered species.
“Due to the inherent population size constraints associated with housing animals in zoos and the logistical, financial, and practical challenges related to translocations, many healthy, fertile animals may never reproduce, even for highly endangered species [33].”
From The Concept of Agency, Animal Wellbeing, and the Practical Realities of Ex Situ Breeding Programs in Zoos and Aquariums (2024) · cites this paper as [33]
Cites
Human longevity at the cost of reproductive success
Westendorp, R. G. J., & Kirkwood, T. B. L. (1998) · Nature · doi:10.1038/25519 · Cited by 607 · see citing works
Reproductive effort decreases antibody responsiveness
Deerenberg, C. M., Arpanius, V., Daan, S., & Bos, N. A. (1997) · Proceedings of the Royal Society B Biological Sciences · doi:10.1098/rspb.1997.0141 · Cited by 442 · see citing works
Progesterone action in breast, uterine, and ovarian cancers
Diep, C. H., Daniel, A. R., Mauro, L. J., Knutson, T. P., & Lange, C. A. (2015) · Journal of Molecular Endocrinology · doi:10.1530/jme-14-0252 · Cited by 191 · see citing works
Safety concerns and health benefits associated with oral contraception
Burkman, R. T., Schlesselman, J. J., & Zieman, M. (2004) · American Journal of Obstetrics and Gynecology · doi:10.1016/j.ajog.2004.01.061 · Cited by 188 · see citing works
Reproductive problems directly attributable to long-term captivity--asymmetric reproductive aging
Hermes, R., Hildebrandt, T. B., & Göritz, F. (2004) · Animal Reproduction Science · doi:10.1016/j.anireprosci.2004.05.015 · Cited by 155 · see citing works
EFFECTS OF MATERNAL AND PEER SEPARATIONS ON YOUNG MONKEYS
Suomi, S. J., Collins, M. L., Harlow, H. F., & Ruppenthal, G. C. (1976) · Journal of Child Psychology and Psychiatry · doi:10.1111/j.1469-7610.1976.tb00382.x · Cited by 117 · see citing works
Sexual Motivation in the Male Rat: The Role of Primary Incentives and Copulatory Experience
López, H. H., Olster, D. H., & Ettenberg, A. (1999) · Hormones and Behavior · doi:10.1006/hbeh.1999.1535 · Cited by 111 · see citing works
Hermes, R. E., Hildebrandt, T. B., Walzer, C., Göritz, F., Patton, M. L., Silinski, S., Anderson, M. J., Reid, C., Wibbelt, G., Tomasova, K., et al. (2005) · Theriogenology · doi:10.1016/j.theriogenology.2005.09.002 · Cited by 108 · see citing works
Penfold, L. M., Powell, D., Traylor‐Holzer, K., & Asa, C. S. (2013) · Zoo Biology · doi:10.1002/zoo.21104 · Cited by 89 · see citing works
Self-citationMunson, L. (2006) · Theriogenology · doi:10.1016/j.theriogenology.2006.03.016 · Cited by 85 · see citing works
Dinh, A., Sriprasert, I., Williams, A. R. W., & Archer, D. F. (2015) · Contraception · doi:10.1016/j.contraception.2015.01.008 · Cited by 75 · see citing works
Suppression of the oestrous responses of bitches to the GnRH analogue deslorelin by progestin.
Wright, P. J., Verstegen, J., Onclin, K., Jochle, W., Armour, A., Martin, G. B., & Trigg, T. E. (2001) · PubMed · Cited by 67 · see citing works
Crosier, A. E., Comizzoli, P., Baker, T., Davidson, A., Munson, L., Howard, J., Marker, L. L., & Wildt, D. E. (2011) · Biology of Reproduction · doi:10.1095/biolreprod.110.089417 · Cited by 66 · see citing works
Asa, C. S., Bauman, K. L., Devery, S., Zordan, M., Camilo, G. R., Boutelle, S., & Moresco, A. (2014) · Zoo Biology · doi:10.1002/zoo.21069 · Cited by 51 · see citing works
Self-citationComparing the Health Risks and Benefits of Contraceptive Choices
Kost, K., Forrest, J. D., & Harlap, S. (1991) · Family Planning Perspectives · doi:10.2307/2135450 · Cited by 49 · see citing works
Wachter, B., Thalwitzer, S., Hofer, H., Lonzer, J., Hildebrandt, T. B., & Hermes, R. E. (2010) · Conservation Letters · doi:10.1111/j.1755-263x.2010.00142.x · Cited by 48 · see citing works
Naturally Occurring and Melengestrol Acetate-associated Reproductive Tract Lesions in Zoo Canids
Moresco, A., Munson, L., & Gardner, I. A. (2009) · Veterinary Pathology · doi:10.1354/vp.08-vp-0293-m-fl · Cited by 43 · see citing works
Proliferative Endometrial Lesions in a Group Of Seba's Short-Tailed Bats (Carollia perspicillata)
Napier, J. E., Caron, S., Reavill, D. R., Murphy, H. W., & Garner, M. M. (2009) · Journal of Zoo and Wildlife Medicine · doi:10.1638/2007-0161.1 · Cited by 13 · see citing works
Wiese (2000) · doi:10.1002/1098-2361(2000)19:5
Flagged first, then by citations
Cited by
Sorted by citations
Herrick, J. R. (2019) · Biology of Reproduction · doi:10.1093/biolre/ioz025 · Cited by 158 · see citing works
Advances in Applied Zoo Animal Welfare Science
Ward, S. J., Sherwen, S., & Clark, F. E. (2018) · Journal of Applied Animal Welfare Science · doi:10.1080/10888705.2018.1513842 · Cited by 78 · see citing works
No Room at the Zoo: Management euthanasia and animal welfare
Browning, H. (2018) · Journal of Agricultural and Environmental Ethics · doi:10.1007/s10806-018-9741-8 · Cited by 27 · see citing works
Issues Surrounding Surplus Animals in Zoos
Bertelsen, M. F. (2018) · Elsevier eBooks · doi:10.1016/b978-0-323-55228-8.00023-0 · Cited by 25 · see citing works
Integrating individual animal and population welfare in zoos and aquariums
DiVincenti, L., McDowell, A., & Herrelko, E. S. (2023) · Animals · doi:10.3390/ani13101577 · Cited by 17 · see citing works
Sterilization and contraception increase lifespan across vertebrates
Garratt, M., Lagisz, M., Staerk, J., Neyt, C., Stout, M. B., Isola, J. V. V., Cowl, V. B., Driver-Ruiz, N., Franklin, A. D., McDonald, M. M., et al. (2025) · Nature · doi:10.1038/s41586-025-09836-9 · Cited by 9 · see citing works
Hybrid apes in the Anthropocene: Burden or asset for conservation?
Palmer, A., Sommer, V., & Msindai, J. N. (2021) · People and Nature · doi:10.1002/pan3.10214 · Cited by 9 · see citing works
“Killing in the Name of 3R?” The Ethics of Death in Animal Research
Persson, K., Perez, C. R., Louis-Maerten, E., Müller, N. D., & Shaw, D. (2024) · Journal of Agricultural and Environmental Ethics · doi:10.1007/s10806-024-09936-y · Cited by 8 · see citing works
Challenges of operating a multi‐species breeding‐for‐release facility at Perth Zoo, Australia
Mawson, P. R., & Lambert, C. (2016) · International Zoo Yearbook · doi:10.1111/izy.12150 · Cited by 8 · see citing works
Norman, M., & Brando, S. (2024) · Journal of Zoological and Botanical Gardens · doi:10.3390/jzbg5040038 · Cited by 7 · see citing works
“Due to the inherent population size constraints associated with housing animals in zoos and the logistical, financial, and practical challenges related to translocations, many healthy, fertile animals may never reproduce, even for highly endangered species [33].”
Hutchins, M., Wiese, R. J., & Smith, B. (2018) · Cambridge University Press eBooks · doi:10.1017/9781108183147.001 · Cited by 6 · see citing works
Tibary, A. (2017) · Frontiers in Veterinary Science · doi:10.3389/fvets.2017.00114 · Cited by 5 · see citing works
Giraud, G., Wandia, I. N., Hambuckers, A., Nagelmackers, F. D. T., Deleuze, S. C., Huynen, M., & Brotcorne, F. (2025) · International Journal of Primatology · doi:10.1007/s10764-025-00520-3 · Cited by 3 · see citing works
Consolacion, J., Ceacero, F., Ny, V., Kotrba, R., Illek, J., Škorič, M., Serralle, M., Soria‐Meneses, P. J., Soler, A. J., & Kokošková, T. (2025) · Reproductive Biology · doi:10.1016/j.repbio.2025.100997 · Cited by 2 · see citing works
Picone, S. L., Sherman, W. C., Sadler, R. A., France, N. R., Herman, A., Kinzley, C., & Minier, D. E. (2024) · Zoo Biology · doi:10.1002/zoo.21863 · Cited by 2 · see citing works
The Growing Pain of Animal Welfare Weaponization: Get the Ghost Out of the Machine
Powell, D., & Watters, J. V. (2025) · Zoo Biology · doi:10.1002/zoo.70044 · Cited by 1 · see citing works
Female Infertility in Zoo Animals
Christensen, B. W. (2018) · Elsevier eBooks · doi:10.1016/b978-0-323-55228-8.00021-7 · Cited by 1 · see citing works
Changes in Reproductive Management
Asa, C. S. (2018) · Elsevier eBooks · doi:10.1016/b978-0-323-55228-8.00022-9 · Cited by 1 · see citing works
Self-citation
- Authors
- Asa, C.
- Affiliations
- Saint Louis Zoo (US)
- Corresponding author
- Asa, Cheryl
- Venue
- Zoo Biology
- Publisher
- Wiley
- Published
- 2016-05
- Volume
- 35
- Issue
- 3
- Pages
- 183-186
- ISSN
- 0733-3188 (ISSN-L)
- OpenAlex
- W2402019012
- Cited by
- 18
- References
- 19
- Citations by year
- 2025: 4 · 2024: 3 · 2023: 1 · 2021: 1 · 2019: 1 · 2018: 6 · 2017: 1 · 2016: 1
- FWCI
- 4.60
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Zoo Biology (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Veterinary › Small Animals › Animal Behavior and Welfare Studies
- Physical Sciences › Environmental Science › Management, Monitoring, Policy and Law › Conservation, Ecology, Wildlife Education
- Physical Sciences › Environmental Science › Ecology › Wildlife Ecology and Conservation
- Keywords
- zoo animal management, aquarium animals, reproductive management, contraception, euthanasia, breeding objectives, population sustainability, animal welfare, captive breeding
- MeSH terms
- Animals, Animal Husbandry, Animals, Zoo, Breeding, Conservation of Natural Resources, Housing, Animal
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