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spayvac for humane wildlife population control

Three single-dose deer trials with SpayVac pZP vaccine demonstrated fertility control

 Deer in urban and suburban areas can contribute to animal-vehicle collisions, disease transmission, and damage to

vegetation. Immunocontraception is an attractive management tool for these populations. Three SpayVac trials in deer

demonstrated fertility control:

- 41 free-ranging fallow deer (Dama dama) were vaccinated with a single injection of SpayVac, and none of them

became pregnant for 3 years following treatment compared to 97% of untreated deer found pregnant each year year (see Fraker et al., 2002 for details).

- 38 free-ranging white-tailed deer (Odocoileus virginianus) were given a single injection of SpayVac, and none of

them became pregnant during the first 2 years after vaccination compared to 78% of untreated deer found pregnant each year (see Locke et al., 2007 for details).

- 5 captive white-tailed deer were given a single injection of SpayVac, and none of them became pregnant during

the next 3 years of the study compared to 100% of the control deer (see Miller et al., 2009 for the full report).

Three trials in horses demonstrate fertility control with SpayVac

There are currently over 75,000 feral horses (Equus ferus caballus) and burros (E. asinus) on U.S. public lands, but the appropriate management level is set at 27,000.  Concerns about the impacts that these free-ranging horses have on shared rangelands has prompted the Bureau of Land Management to remove over 45,000 horses to off-range holding facilities, which costs approximately $50 million per year.  Certain Native-American lands have an equally or bigger population of wild horses. Immunocontraception offers a humane alternative to managing these free-ranging horse populations, and three SpayVac trials in horses demonstrated fertility control:

- 12 captive mares were given a single injection of SpayVac, which dropped pregnancy rates to 0, 17, 17 and 17% for 1 to 4 years post-treatment, respectively, compared to 75, 75, 88 and 100% for untreated mares.  Killian et al., 2008 provides additional details about this study.

- 14 captive mares were given a single injection of SpayVac, and 3-4 months post-vaccination, 93% of the mares stopped cycling compared to control mares that continued to cycle.  This study was also designed as a safety trial and demonstrated no adverse health effects to any treated mares – vaccine effects were solely localized to the ovaries (see Bechert et al., 2013 for more information).

- 30 feral mares maintained in holding facilities were given a single injection of SpayVac, and fertility rates in the treated group dropped to 13, 47, and 43% compared to 100, 98 and 100% in controls for 1 to 3 years post-vaccination, respectively (see Roelle et al., 2017 for additional details).


Other Species



Although grey seals (Halichoerus grypus) were hunted earlier, pup production on Sable Island in Nova Scotia has been increasing exponentially at an annual rate of 12.8% for the past four decades (Bowen et al., 2003, Journal Marine Science 60(6): 1265–1274).  SpayVac immunocontraception offers a humane alternative to culling to control these populations.  In 1992, 101 wild female grey seals were treated with a single injection of SpayVac, and fertility rates dropped from an average of 70% for controls to 12% for treated animals for 10+ years.  See Brown et al. 1997 for details about the initial 5-year study.



As free-ranging populations of African (Loxodonta africana) and Asian elephants (Elephas maximus) become increasingly confined to smaller ranges, concerns grow about human–elephant conflicts and negative impacts on flora and fauna.  A group of 6 captive African elephants were vaccinated with a single injection of SpayVac, and pZP antibody titers were first detected 4 weeks post-vaccination but did not peak until 1 year, after which they remained consistently elevated through 7+ years.  Additional research is needed to determine actual contraceptive efficacy in these animals and how SpayVac could work in Asian elephants.  See Bechert and Fraker, 2016 for details about this promising initial trial.



SpayVac has the potential to serve as a single-dose, multi-year contraceptive vaccine in a variety of different mammalian species.  For example, Rhesus macaques (Macaca mulatta) are viewed as overabundant pest species in India, and introduced free-ranging macaques in Florida pose a health danger to humans, because 25% of the population surveyed are infected with herpesvirus, which can spread to humans.  SpayVac is a humane tool that could be applied to both of these populations to keep numbers in check, reduce human-animal conflict, and diminish the risk of disease transmission.  


Bilbiography of Studies


Bechert and Fraker 2018. Twenty Years of SpayVac® Research: Potential for Regulating Feral Horse and Burro Populations in the U.S.  Human Wildlife Interactions 12(1)13: 

Roelle et al. 2017. Efficacy of SpayVac® as a contraceptive in feral horses. Wildlife Society Bulletin 41(1):107-15.-----

Bechert and Wagner. 2017. Identifying immunocontracepted mares using IgG isotypes. Proceedings from the 8th International Wildlife Fertility Control Conference-----

Bechert and Fraker. 2016. The response of African elephants to a single-dose of SpayVac®, a pZP contraceptive vaccine, over a 7-year period. Pachyderm 57:97-108.-----

Bechert et al. 2013. Effects of two porcine zona pellucida immunocontraceptive vaccines on ovarian activity in horses. Journal of Wildlife Management 77(7):1386-1400. --

Miller et al. 2009. Factors contributing to the success of a single-shot, multiyear pZP immunocontraceptive vaccine for white-tailed deer. Human-Wildlife Conflicts 3(1):103-15. -----

Killian et al. 2008. Four-year contraception rates of mares treated with single-injections porcine zona pellucida and GnRH vaccines and intrauterine devices. Wildlife Research 35:103-15. ----

Kirkpatrick and Turner. 2008. Achieving population goals in a long-lived wildlife species (Equus caballus) with contraception. Wildlife Research 35:513-19. -----

Locke et al. 2007. Effectiveness of SpayVac® for reducing white-tailed deer fertility. Journal of Wildlife Diseases 43(4):726-30.-----

Kirkpatrick and Turner 2007. Immunocontraception and increased longevity in equids. Zoo Biology 26:237-44.-----

Hernandez et al. 2006. Effects of SpayVac® on urban female white-tailed deer movements. Wildlife Society Bulletin 34:1430-34.-----

Fraker et al. 2002. Long-lasting, single-dose immunocontraception of feral fallow deer in British Columbia. Journal of Wildlife Management 66:1141-47.-----

Brown et al. 1997. Evidence for a long-lasting single administration vaccine in wild grey seals. Journal of Reproductive Immunology 35:43–51.-----

Brown et al. 1997. Temporal trends in antibody production in captive grey, harp and hooded seals to a single administration of immunocontraceptive vaccine. Journal of Reproductive Immunology 35:53–64.

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If you want to discuss SpayVac or what is new with pZP vaccine, we can usually be reached during the following hours.  (All times are Eastern Time Zone)

SpayVac for Wildlife Inc.

725 University Row-- Ste. #439 Madison, WI 53705 USA

1 (877) 510-6812



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