Subscribe here for SpayVac info

Wild Horses


Three single-dose trials in horses demonstrate fertility control with SpayVac

There are currently over 81,000 feral horses (Equus ferus caballus) and burros (E. asinus) on U.S. public lands managed by BLM, but the appropriate management level is set around 25,000. Concerns about the impacts that these free-ranging horses have on shared rangelands has prompted the Bureau of Land Management to remove over 55,000 horses to off-range holding facilities, where costs exceed $50 million per year.  Certain Native-American lands have an equal or larger population of wild horses. Navajo Nation may have the largest population of wild horses and burros in the USA.  Hopi Nation and Yakima Nation are also struggling with wild horse and wild burro populations.  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).



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).



Other Species: Seals, SpayVac, Macaques



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.  One-hundred one (n=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 with a single-dose.  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.


More information on trials done with SpayVac on Macaques in Hong Kong and  in  Puerto  Rico  will be posted here soon.

The SpayVac Technology Advantage

The Key is Antigen Presentation to Immune Cells


SpayVac is formulated in a patented, leading-edge delivery platform that is the cornerstone of our vaccine development pipeline.  The platform is DepoVax.  DepoVax is a patented vaccine delivery formulation that provides controlled and prolonged exposure of antigens plus adjuvant to the immune system. The result is a strong, specific, and sustained immune response with the capability for single-dose effectiveness.  It offers a robust and scalable engine for delivering many different targets that activate and direct immuneocontraception in a controlled, impactful way.

Why this matters:


Our proprietary advantage starts with a groundbreaking delivery formulation that is a powerful mechanism to present the pZP antigen to the animal's immune system, and sustain this presentation over a long timeframe. This platform utilizes a proprietary, extraordinarily stable “NO-RELEASE” delivery system utilizing highly engineered liposomes, which mitigates the propensity for antigens to break down, thereby extending the stimulation of the immune response. 

What is a liposome?


A liposome is a small sphere, made out of the same material as a cell membrane. Liposomes can be filled with drugs, and used to deliver antigens for vaccines.   There are many advantages of liposomes.  The biggest advantage is the cell membrane and the liposome membrane consist of the same phospholipid bilayer. This biocompatibility makes the targeted cells readily available to accept the active content (pZP in the case of SpayVac).

What is VacciMax®


VacciMax is a patented vaccine delivery formulation that provides controlled and prolonged exposure of antigens plus adjuvant to the immune system. The result is a strong, specific, and sustained immune response with the capability for single-dose effectiveness, which was proven in multiple trials with SpayVac.

What is DepoVax™


DepoVax is a modified water-free version of VacciMax. The DepoVax platform is a combination of antigens, plus adjuvant (immune enhancers) formulated in liposomes and then in oil. Having access to both versions allows SFW to offer vaccine as either a lyophilized cake or in pre-filled syringes.

The Superior Immune Response


Resuspending liposomes in oil instead of aqueous solutions has recently been shown to dramatically increase the level and persistence of an immune response and forms the basis of the novel vaccine formulations, Vaccimax and Depovax , which we can apply to SpayVac pzp vaccine for wildlife



Bilbiography of Studies

Bechert, Rohde, Freer, Wagner. 2018.  IgG4/7 responses correlate with contraception in mares vaccinated with SpayVac.  Theriogenology 121:168-174

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.

Contact Us

If you want to contact us for more information, fill out the form below

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

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.

Fitchburg, Wisconsin, USA and Victoria, BC, Canada

1 (877) 510-6812



09:00 am – 07:00 pm


09:00 am – 07:00 pm


09:00 am – 07:00 pm


09:00 am – 07:00 pm


09:00 am – 07:00 pm