Register      Login
Wildlife Research Wildlife Research Society
Ecology, management and conservation in natural and modified habitats
RESEARCH ARTICLE

Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations

Meeghan E. Gray A B E , David S. Thain A , Elissa Z. Cameron C and Lowell A. Miller D
+ Author Affiliations
- Author Affiliations

A Department of Animal Biotechnology, University of Nevada, Reno, 1664 North Virginia Street MS 202, Reno, NV 89557, USA.

B Program in Ecology, Evolution and Conservation Biology, University of Nevada, Reno, Reno, NV 89557, USA.

C Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, 0002 Pretoria, South Africa.

D National Wildlife Research Center, USDA/-APHIS/WS/NWRC, Fort Collins, CO 80521, USA.

E Corresponding author. Email: mgray@cabnr.unr.edu

Wildlife Research 37(6) 475-481 https://doi.org/10.1071/WR09175
Submitted: 15 December 2009  Accepted: 28 August 2010   Published: 18 October 2010

Abstract

Context.: Contraception is increasingly used as a management technique to reduce fertility in wildlife populations; however, the feasibility of contraceptive formulations has been limited until recently because they have required multiple treatments to achieve prolonged infertility.

Aims.: We tested the efficacy and evaluated potential side effects of two contraceptive formulations, a porcine zona pellucida (PZP) formulation, SpayVac® and a gonadotrophin-releasing hormone (GnRH) formulation GonaCon-B™, in a population of free-roaming feral horses (Equus caballus). Both formulations were developed to provide several years of infertility with one injection.

Methods.: Females were treated in June 2005 with either GonaCon-B (n = 24), SpayVac (n = 20), adjuvant only (n = 22), or received no injection (n = 18). Females were monitored for fertility status year round for 3 years after treatment.

Key results.: Both contraceptive treatments significantly reduced fertility for 3 years. Fertility rates for GonaCon-B mares were 39%, 42% and 31%, respectively, and 37%, 50% and 44% for SpayVac mares. During the same seasons, 61%, 67% and 76% of control females were fertile. We found no significant effects from contraceptive treatment on the sex ratio of foals, birthing season or foal survival.

Conclusions.: These results demonstrated that both vaccines are capable of significantly reducing fertility for several years without boosters.

Implications.: Contraceptive vaccines examined in the present study represent a useful tool for the management of feral horses, because of their being efficacious for 3 years in the absence of booster immunisations.

Additional keywords: field study, GnRH vaccine, immunocontraception, population control, PZP vaccine, side effects, wild horses.


References

Asa, C. S., Fischer, M. T., Bauman, J. E., Houston, E. W., Bauman, K. L., Hagbag, P. K., and Read, B. W. (1996). Ovulatory cycles and anovulatory periods in the addax (Addax nasomaculatus). Journal of Reproduction and Fertility 107, 119–124.
Ovulatory cycles and anovulatory periods in the addax (Addax nasomaculatus).Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK28XmtFOlurs%3D&md5=6d26a40fe557d9c9aa9fa9debfca3e14CAS | 8699424PubMed |

Asa, C. S., Bauman, J. E., Houston, E. W., Fischer, M. T., Read, B., Brownfield, C. M., and Roser, J. F. (2001). Patterns of excretion of fecal estrodial and progesterone and urinary chorionic gonadotropin in Grevy’s zebra (Equus grevyi): ovulatory cycles and pregnancy. Zoo Biology 20, 185–195.
Patterns of excretion of fecal estrodial and progesterone and urinary chorionic gonadotropin in Grevy’s zebra (Equus grevyi): ovulatory cycles and pregnancy.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3MXmvVagtbk%3D&md5=343eb11d6f911da84d11c5eedcb5bdeeCAS |

Baker, D. L., Wild, M. A., Conner, M. M., Ravivarapu, H. B., Dunn, R. L., and Nett, T. M. (2002). Effects of GnRH agonist leuprolide on reproduction and behavior in female wapiti Cervus elaphus nelsoni. Reproduction (Supplement) 60, 155–167.
| 1:CAS:528:DC%2BD38XnsFGksL8%3D&md5=dbbbc213c150641c7d1d84d34f85e899CAS |

Bartholow, J. (2007). Economic benefit of fertility control in wild horse populations. Journal of Wildlife Management 71, 2811–2819.
Economic benefit of fertility control in wild horse populations.Crossref | GoogleScholarGoogle Scholar |

Beever, E. A., and Brussard, P. F. (2000). Examining ecological consequences of feral horse grazing using exclosures. Western North American Naturalist 60, 236–254.

Beever, E. A., and Brussard, P. F. (2004). Community- and landscape-level responses of reptiles and small mammals to feral-horse grazing in the Great Basin. Journal of Arid Environments 59, 271–297.
Community- and landscape-level responses of reptiles and small mammals to feral-horse grazing in the Great Basin.Crossref | GoogleScholarGoogle Scholar |

Beever, E. A., and Herrick, J. E. (2006). Effects of feral horses in Great Basin landscapes on soils and ants: direct and indirect mechanisms. Journal of Arid Environments 66, 96–112.
Effects of feral horses in Great Basin landscapes on soils and ants: direct and indirect mechanisms.Crossref | GoogleScholarGoogle Scholar |

Berger, J. (1986). ‘Wild Horses of the Great Basin.’ (University of Chicago Press: Chicago, IL.)

Brown, R. G., Bowen, W. D., Eddington, J. D., Kimmins, W. C., Mezei, M., Parsons, J. L., and Pohajdak, B. (1997). Evidence for a long-lasting single administration contraceptive in wild grey seals. Journal of Reproductive Immunology 35, 43–51.
Evidence for a long-lasting single administration contraceptive in wild grey seals.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK2sXms1eqs74%3D&md5=7c00904bcb7bb999c75fcc01a341faa1CAS | 9373857PubMed |

Cameron, E. Z. (2004). Facultative adjustment of mammalian sex ratios in support of the Trivers–Willard hypothesis: evidence for a mechanism. Proceedings. Biological Sciences 271, 1723–1728.
Facultative adjustment of mammalian sex ratios in support of the Trivers–Willard hypothesis: evidence for a mechanism.Crossref | GoogleScholarGoogle Scholar |

Cameron, E. Z., and Linklater, W. L. (2000). Individual mares bias investment in sons and daughters in relation to their condition. Animal Behaviour 60, 359–367.
Individual mares bias investment in sons and daughters in relation to their condition.Crossref | GoogleScholarGoogle Scholar | 11007645PubMed |

Cameron, E. Z., and Linklater, W. L. (2007). Extreme sex ratio variation in relation to change in condition around conception. Biology Letters 3, 395–397.
Extreme sex ratio variation in relation to change in condition around conception.Crossref | GoogleScholarGoogle Scholar | 17439844PubMed |

Conner, M. M., Baker, D. L., Wild, M. A., Powers, J. G., Hussain, M. D., Dunn, R. L., and Nett, T. M. (2007). Fertility control in free-ranging elk using gonadotropin-releasing hormone agonist leuprolide: effects on reproduction, behavior, and body condition. Journal of Wildlife Management 71, 2346–2356.
Fertility control in free-ranging elk using gonadotropin-releasing hormone agonist leuprolide: effects on reproduction, behavior, and body condition.Crossref | GoogleScholarGoogle Scholar |

Conover, M. R., and Chasko, G. G. (1985). Nuisance Canada goose problems in the eastern United States. Wildlife Society Bulletin 13, 228–233.

Curtis, P. D., Pooler, R. L., Richmond, M. E., Miller, L. A., Mattfeld, G. F., and Quimby, F. W. (2002). Comparative effects of GnRH and porcine zona pellucida (PZP) immunocontraceptive vaccines for controlling reproduction in white-tailed deer (Odocoileus virginianus). Reproduction (Supplement) 60, 131–141.
| 1:CAS:528:DC%2BD38XnsFGksL4%3D&md5=cb0846e61586c4975b0d4c5dd70869e0CAS |

Delsink, A. K., van Altena, J. J., Kirkpatrick, J., Grobler, D., and Fayrer-Hosken, R. A. (2002). Field applications of immunocontraception in African elephants Loxodonta africana. Reproduction (Supplement) 60, 117–124.
| 1:STN:280:DC%2BD38vmtFCjsw%3D%3D&md5=ea613e7681ff3af1857330277263aaa1CAS |

Fayrer-Hosken, R. A., Grobler, D., van Altena, J. J., Bertschinger, H. J., and Kirkpatrick, J. F. (2000). Immunocontraception of African elephants. Nature 407, 149.
Immunocontraception of African elephants.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3cXmsl2gtr4%3D&md5=88449597cf79c07ae9fea4c2795ccc23CAS |

Fayrer-Hosken, R. A., Barber, M. R., Crane, M., Collins, T., and Hodgden, R. (2002). Differences in immunocontraceptive responses in white-tailed deer (Odocoileus virginianus) and goats (Capra hircus). Reproduction (Cambridge, England) Supplement 60, 125–129.
| 1:STN:280:DC%2BD38vmtFCjsA%3D%3D&md5=d7557697ec6d9d598414c41eba22ad1eCAS | 12220152PubMed |

Feist, J. D., and McCullough, D. R. (1975). Reproduction in feral horses. Journal of Reproduction and Fertility. Supplement 23, 13–18.
| 1060766PubMed |

Fraker, M. A., Brown, R. G., Gaunt, G. E., Kerr, J. A., and Pohajdak, B. (2002). Long-lasting, single-dose immunocontraception of feral fallow deer in British Columbia. Journal of Wildlife Management 66, 1141–1147.
Long-lasting, single-dose immunocontraception of feral fallow deer in British Columbia.Crossref | GoogleScholarGoogle Scholar |

Frank, K. M., Lyda, R. O., and Kirkpatrick, J. F. (2005). Immunocontraception of captive exotic species IV. Species differences in response to the porcine zona pellucida vaccine, timing of booster inoculations, and procedural failures. Zoo Biology 24, 349–358.
Immunocontraception of captive exotic species IV. Species differences in response to the porcine zona pellucida vaccine, timing of booster inoculations, and procedural failures.Crossref | GoogleScholarGoogle Scholar |

Garrott, R. A., and Taylor, L. (1990). Dynamics of a feral horse population in Montana USA. Journal of Wildlife Management 54, 603–612.
Dynamics of a feral horse population in Montana USA.Crossref | GoogleScholarGoogle Scholar |

Garrott, R. A., Cook, J. G., Bernoco, M. M., Kirkpatrick, J. F., Cadwell, L. L., Cherry, S., and Tiller, B. (1998). Antibody response of elk immunized with porcine zona pellucida. Journal of Wildlife Diseases 34, 539–546.
| 1:STN:280:DyaK1czntFymsA%3D%3D&md5=21c66d670ec409ea91d666b5d29b3cb0CAS | 9706563PubMed |

Gray, M. E., and Cameron, E. Z. (2010). Does contraceptive treatment in wildlife result in side-effects? A review of quantitative and anecdotal evidence. Reproduction 139, 45–55.
Does contraceptive treatment in wildlife result in side-effects? A review of quantitative and anecdotal evidence.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXovVWntQ%3D%3D&md5=7156de5f649887ddf4f1c5f517e49a19CAS | 19656957PubMed |

Heilmann, T. J., Garrott, R. A., Cadwell, L. L., and Tiller, B. L. (1998). Behavioral response of free-ranging elk treated with an immunocontraceptive vaccine. Journal of Wildlife Management 62, 243–250.
Behavioral response of free-ranging elk treated with an immunocontraceptive vaccine.Crossref | GoogleScholarGoogle Scholar |

Henderson, D. W., Warren, R. J., Cromwell, J. A., and Hamilton, R. J. (2000). Responses of urban deer to a 50% reduction in local herd density. Wildlife Society Bulletin 28, 902–910.

Hernandez, S., Locke, S. L., Cook, M. W., Harveson, L. A., Davis, D. S., Lopez, R. R., Silvy, N. J., and Fraker, M. A. (2006). Effects of SpayVac® on urban female white-tailed deer movements. Wildlife Society Bulletin 34, 1430–1434.
Effects of SpayVac® on urban female white-tailed deer movements.Crossref | GoogleScholarGoogle Scholar |

Houston, A. I., McNamara, J. M., Barta, Z., and Klasing, K. C. (2007). The effect of energy reserves and food availability on optimal immune defence. Proceedings. Biological Sciences 274, 2835–2842.
The effect of energy reserves and food availability on optimal immune defence.Crossref | GoogleScholarGoogle Scholar |

Keiper, R., and Houpt, K. (1984). Reproduction in feral horses: an eight year study. American Journal of Veterinary Research 45, 991–995.
| 1:STN:280:DyaL2c3ivFGnsg%3D%3D&md5=c2079eeb28de9709d4321cf0b824ab74CAS | 6732036PubMed |

Killian, G., Miller, L., Rhyan, J., and Doten, H. (2006). Immunocontraception of Florida feral swine with a single-dose GnRH vaccine. American Journal of Reproductive Immunology 55, 378–384.
Immunocontraception of Florida feral swine with a single-dose GnRH vaccine.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD28Xltlehtr4%3D&md5=7dd009c3b143ef233270846a1b9f6cf1CAS | 16635212PubMed |

Killian, G., Thain, D., Diehl, N. K., Rhyan, J., and Miller, L. (2008). Four-year contraception rates of mares treated with single-injection porcine zona pellucida and GnRH vaccines and intrauterine devices. Wildlife Research 35, 531–539.
Four-year contraception rates of mares treated with single-injection porcine zona pellucida and GnRH vaccines and intrauterine devices.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXht1KrtLjJ&md5=1a4bb122fa70e163f23706154cfc45deCAS |

Kirkpatrick, J. F. (2007). Measuring the effects of wildlife contraception: the argument for comparing apples with oranges. Reproduction, Fertility and Development 19, 548–552.
Measuring the effects of wildlife contraception: the argument for comparing apples with oranges.Crossref | GoogleScholarGoogle Scholar |

Kirkpatrick, J. F., and Turner, J. W. (1991). Compensatory reproduction in feral horses. Journal of Wildlife Management 55, 649–652.
Compensatory reproduction in feral horses.Crossref | GoogleScholarGoogle Scholar |

Kirkpatrick, J. F., and Turner, A. (2003). Absence of effects from immunocontraception on seasonal birth patterns and foal survival among barrier island wild horses. Journal of Applied Animal Welfare Science 6, 301–308.
Absence of effects from immunocontraception on seasonal birth patterns and foal survival among barrier island wild horses.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2cXhvVOju7g%3D&md5=af2b0f55e48145a8789081509c873c97CAS | 14965784PubMed |

Kirkpatrick, J. F., Liu, I. K. M., and Turner, J. W. Jr. (1990). Remotely-delivered immunocontraception in feral horses. Wildlife Society Bulletin 18, 326–330.

Kirkpatrick, J. F., Liu, I. K. M., Turner, J. W., Naugle, R., and Keiper, R. (1992). Long-term effects of porcine zonae pellucidae immunocontraception on ovarian function in feral horses Equus caballus. Journal of Reproduction and Fertility 94, 437–444.
Long-term effects of porcine zonae pellucidae immunocontraception on ovarian function in feral horses Equus caballus.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK38XktVWitro%3D&md5=dc67a85d48cc45f9a560b252ae1b1f7eCAS | 1317449PubMed |

Kirkpatrick, J. F., Calle, P. P., Kalk, P., Liu, I. K. M., and Turner, J. W. (1996). Immunocontraception of captive exotic species 2: Formosan sika deer Cervus nippon taiouanus, axis deer Cervus axis, Himalayan tahr Hemitragus jemlahicus, Roosevelt elk Cervus elaphus roosevelti, Reeves’ muntjac Muntiacus reevesi, and sambar deer Cervus unicolor. Journal of Zoo and Wildlife Medicine 27, 482–495.

Lane, V. M., Liu, I. K. M., Casey, K., vanLeeuwen, E. M. G., Flanagan, D. R., Murata, K., and Monro, C. (2007). Inoculation of female black bears (Ursus americanus) with partially purified porcine zona pellucidae limits cub production. Reproduction, Fertility and Development 19, 617–625.
Inoculation of female black bears (Ursus americanus) with partially purified porcine zona pellucidae limits cub production.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD2sXos1Kgt78%3D&md5=a97ab567e63e6ea084644af2518b435aCAS |

Lauber, T. B., Knuth, B. A., Tantillo, J. A., and Curtis, P. D. (2007). The role of ethical judgments related to wildlife fertility control. Society & Natural Resources 20, 119–133.
The role of ethical judgments related to wildlife fertility control.Crossref | GoogleScholarGoogle Scholar |

Levin, P. S., Ellis, J., Petrik, R., and Hay, M. E. (2002). Indirect effects of feral horses on estuarine communities. Conservation Biology 16, 1364–1371.
Indirect effects of feral horses on estuarine communities.Crossref | GoogleScholarGoogle Scholar |

Lucas, Z., Raeside, J. I., and Betteridge, K. J. (1991). Noninvasive assessment of the incidences of pregnancy and pregnancy loss in the feral horses of Sable Island. Journal of Reproduction and Fertility. Supplement 44, 479–488.
| 1:STN:280:DyaK387nslamtA%3D%3D&md5=955437a4ee9df0ef7a4a83ca1fc38e58CAS | 1795292PubMed |

Massei, G., Cowan, D. P., Coats, J., Gladwell, F., Lane, J. E., and Miller, L. A. (2008). Effect of GnRH vaccine GonaCon on the fertility, physiology and behavior of wild boar. Wildlife Research 35, 540–547.
Effect of GnRH vaccine GonaCon on the fertility, physiology and behavior of wild boar.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXht1KrtLjP&md5=4490e4008ec6b3ecb6831494b84fbdbaCAS |

McShea, W. J., Monfort, S. L., Hakim, S., Kirkpatrick, J., Liu, I., Turner, J. W. Jr, Chassy, L., and Munson, L. (1997). The effect of immunocontraception on the behavior and reproduction of white-tailed deer. Journal of Wildlife Management 61, 560–569.
The effect of immunocontraception on the behavior and reproduction of white-tailed deer.Crossref | GoogleScholarGoogle Scholar |

Miller, L. A., Johns, B. E., and Killian, G. J. (2000a). Immunocontraception of white-tailed deer with GnRH vaccine. American Journal of Reproductive Immunology 44, 266–274.
Immunocontraception of white-tailed deer with GnRH vaccine.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DC%2BD3M7lt1Gnug%3D%3D&md5=ebd98e412805199d18c771a4e0b7b7b4CAS | 11125787PubMed |

Miller, L. A., Johns, B. E., and Killian, G. J. (2000b). Immunocontraception of white-tailed deer using native and recombinant zona pellucida vaccines. Animal Reproduction Science 63, 187–195.
Immunocontraception of white-tailed deer using native and recombinant zona pellucida vaccines.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD3cXmtlOmtLw%3D&md5=08c90e8688d784a237beaccbce2a004fCAS | 10989229PubMed |

Miller, L. A., Rhyan, J. C., and Drew, M. (2004). Contraception of bison by GnRH vaccine: a possible means of decreasing transmission of brucellosis in bison. Journal of Wildlife Diseases 40, 725–730.
| 1:CAS:528:DC%2BD2MXhsV2ht74%3D&md5=c9bf706c2068a19116f85927d709cdfeCAS | 15650090PubMed |

Miller, L. A., Gionfriddo, J. P., Fagerstone, K. A., Rhyan, J. C., and Killian, G. J. (2008). The single-shot GnRH immunocontraceptive vaccine (GonaCon™) in white-tailed deer: comparison of several GnRH preparations. American Journal of Reproductive Immunology 60, 214–223.
The single-shot GnRH immunocontraceptive vaccine (GonaCon™) in white-tailed deer: comparison of several GnRH preparations.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BD1cXhtFKrsbzP&md5=66115397852b0d6287e1000b36f7c66cCAS | 18782282PubMed |

Monard, A. M., Duncan, P., Fritz, H., and Feh, C. (1997). Variations in the birth sex ratio and neonatal mortality in a natural herd of horses. Behavioral Ecology and Sociobiology 41, 243–249.
Variations in the birth sex ratio and neonatal mortality in a natural herd of horses.Crossref | GoogleScholarGoogle Scholar |

Munson, L., Bauman, J. E., Asa, C. S., Jochle, W., and Trigg, T. E. (2001). Efficacy of the GnRH-analogue deslorelin for suppression of the oestrous cycle in cats. Journal of Reproduction and Fertility. Supplement 57, 269–273.
| 1:CAS:528:DC%2BD3MXktF2qtrk%3D&md5=f9f43d7e7697cf8e151a78afc4dbddfbCAS | 11787161PubMed |

Naugle, R. E., Rutberg, A. T., Underwood, H. B., Turner, J. W., and Liu, I. K. M. (2002). Field testing of immunocontraception on white-tailed deer (Odocoileus virginianus) on Fire Island National Seashore, New York, USA. Reproduction (Cambridge, England) Supplement 60, 143–153.
| 1:STN:280:DC%2BD38vmtFCjtg%3D%3D&md5=f97e967666cff1443be050a2ca6485c0CAS | 12220154PubMed |

Nettles, V. F. (1997). Potential consequences and problems with wildlife contraceptives. Reproduction, Fertility and Development 9, 137–143.
Potential consequences and problems with wildlife contraceptives.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaK2s3mt12qtA%3D%3D&md5=84aacde3fea3cf13e06ae9a54f8b3f74CAS |

Oogjes, G. (1997). Ethical aspects and dilemmas of fertility control of unwanted wildlife: an animal welfarist’s perspective. Reproduction, Fertility and Development 9, 163–167.
Ethical aspects and dilemmas of fertility control of unwanted wildlife: an animal welfarist’s perspective.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaK2s3mt12quw%3D%3D&md5=a14d7f36606ad7a04e1f8d473bbdeb03CAS |

Rogers, G. M. (1990). Kaimanawa feral horses and their environmental impacts. New Zealand Journal of Ecology 15, 49–64.

Rutberg, A. T., Naugle, R. E., Thiele, L. A., and Liu, I. K. M. (2004). Effects of immunocontraception on a suburban population of white-tailed deer Odocoileus virginianus. Biological Conservation 116, 243–250.
Effects of immunocontraception on a suburban population of white-tailed deer Odocoileus virginianus.Crossref | GoogleScholarGoogle Scholar |

Shideler, S. E., Ortuno, A. M., Moran, F. M., Morrman, E. A., and Lasley, B. L. (1993). Simple extraction and enzyme immunoassays for estrogen and progesterone metabolites in the feces of Macaca fascicularis during non-conceptive and conceptive ovarian cycles. Biology of Reproduction 48, 1290–1298.
Simple extraction and enzyme immunoassays for estrogen and progesterone metabolites in the feces of Macaca fascicularis during non-conceptive and conceptive ovarian cycles.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK3sXkvVKgt7k%3D&md5=6f04d7003884faafa5d4673ac055bf99CAS | 8318583PubMed |

Stout, R. J., Knuth, B. A., and Curtis, P. D. (1997). Preferences of suburban landowners for deer management techniques: a step towards better communication. Wildlife Society Bulletin 25, 348–359.

Turner, A., and Kirkpatrick, J. F. (2002). Effects of immunocontraception on population, longevity and body condition in wild mares (Equus caballus). Reproduction (Supplement) 60, 187–195.
| 1:CAS:528:DC%2BD38XnsFGksLo%3D&md5=408eacc0d55f8f757feb0215ff8aa883CAS |

Turner, J. W., Liu, I. K. M., and Kirkpatrick, J. F. (1996). Remotely delivered immunocontraception in free-roaming feral burros (Equus asinus). Journal of Reproduction and Fertility 107, 31–35.
Remotely delivered immunocontraception in free-roaming feral burros (Equus asinus).Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DyaK28XmtFOltbo%3D&md5=72d9e9bb239f058daf7f9dc3bc431b4cCAS | 8699431PubMed |

Turner, J. W., Liu, I. K. M., Rutberg, A. T., and Kirkpatrick, J. F. (1997). Immunocontraception limits foal production in free-roaming feral horses in Nevada. Journal of Wildlife Management 61, 873–880.
Immunocontraception limits foal production in free-roaming feral horses in Nevada.Crossref | GoogleScholarGoogle Scholar |

Turner, J. W., Liu, I. K. M., Flanagan, D. R., Rutberg, A. T., and Kirkpatrick, J. F. (2001). Immunocontraception in feral horses: one inoculation provides one year of infertility. Journal of Wildlife Management 65, 235–241.
Immunocontraception in feral horses: one inoculation provides one year of infertility.Crossref | GoogleScholarGoogle Scholar |

Turner, J. W., Liu, I. K. M., Flanagan, D. R., Bynum, K. S., and Rutberg, A. T. (2002). Porcine zona pellucida (PZP) immunocontraception of wild horses (Equus caballus) in Nevada: a 10 year study. Reproduction (Cambridge, England) Supplement 60, 177–186.
| 1:CAS:528:DC%2BD38XnsFGksL0%3D&md5=409f6701d98a0e527a7c0ce8a9b5299bCAS | 12220157PubMed |

Turner, J. W., Liu, I. K. M., Flanagan, D. R., and Rutberg, A. T. (2007). Immunocontraception in wild horses: one inoculation provides two years of infertility. Journal of Wildlife Management 71, 662–667.
Immunocontraception in wild horses: one inoculation provides two years of infertility.Crossref | GoogleScholarGoogle Scholar |

Tutt, J. F. D. (1968). The examination of the mouth for age. In ‘Veterinary Notes for Horse Owners’. (Ed. M. M. Hayes.) pp. 512–526. (Stanley Paul: London.)

Wagner, F. H. (1983). Status of wild horse and burro management on public rangelands. In ‘Transactions of the Forty-eighth North American Wildlife and Natural Resources Conference’. (Ed. K. Sabol.) pp. 116–133. (Wildlife Management Institute: Washington, DC.)

Walter, W. D., Perkins, P. J., Rutberg, A. T., and Kilpatrick, H. J. (2002). Evaluation of immuno contraception in free-ranging suburban white-tailed deer herd. Wildlife Society Bulletin 30, 186–192.

Warren, R. J. (1997). Special issue – deer overabundance. Wildlife Society Bulletin 25, 213–600.

Whyte, I., van Aarde, R., and Pimm, S. L. (1998). Managing the elephants of Kruger National Park. Animal Conservation 1, 77–83.
Managing the elephants of Kruger National Park.Crossref | GoogleScholarGoogle Scholar |

Zalba, S. M., and Cozzani, N. C. (2004). The impact of feral horses on grassland bird communities in Argentina. Animal Conservation 7, 35–44.
The impact of feral horses on grassland bird communities in Argentina.Crossref | GoogleScholarGoogle Scholar |