The ~Texas~ Mustang Project's Blog

Working for better management options and cohabitation through compromise and communication for the American Wild Mustang

SpayVac Fertility Control Study Begins at Pauls Valley, OK

Posted by Texas Mustang Project on April 27, 2011

(Links and resources at the end of BLM’s Press Release)

Bureau of Land Management

Contacts: Paul McGuire (Oklahoma) (405-794-9624) Heather Emmons (Nevada) (775-384-7966) Tom Gorey (Washington, D.C.) (202-912-7420)

For release: Tuesday, April 26, 2011

BLM, USGS Begin New Wild Horse Fertility Control Study

The Bureau of Land Management and the United States Geological Survey  (USGS) have begun a five-year wild horse contraceptive study at the BLM’s short-term holding facility in Pauls Valley, Oklahoma.  The pasture breeding study will test the effectiveness of two formulations of the investigational contraceptive vaccine SpayVac® to determine if the treatment can reduce foaling rates in wild horse mares.
The goal is to see if SpayVac®, a novel formulation of a glycoprotein called porcine zona pellucida (PZP), will provide a longer-term effect than other PZP vaccines currently used by the BLM.  If the vaccine is found to reduce foaling in this controlled setting, it will be considered for use with free-roaming horses to help control population growth rates on the
As the primary agency responsible for management of wild horses on U.S. public lands, the BLM has a need for a long-lasting contraceptive agent to control herd growth rates.  Given the protection afforded by the Wild Free-Roaming Horses and Burros Act of 1971 and a general lack of natural predators, wild horse populations increase at an average rate of 20 percent a year and can quickly exceed the carrying capacity of their ranges.
The BLM, as part of its development of a new wild horse and burro management strategy, has been stepping up its efforts to reduce population growth rates in wild horse herds using contraceptive agents.  A main limitation of the agents currently available is that they are of relatively short duration or need to be administered annually.  Maximizing the duration of contraceptive effectiveness is especially important in wild horses, which in most cases must be captured in order for the treatment to be successfully administered.
In the BLM-USGS study, 90 mares have been treated with either one of two formulations of the vaccine or a placebo.  The mares will be followed for five years to measure anti-PZP antibody levels and compare the foaling rates between treated horses and controls.  Although breeding is not usually allowed to occur in BLM facilities, a clinical trial in this controlled environment will provide critical information on how well SpayVac® works as a contraceptive.
The mares and stallions enrolled in the study were selected from horses already in BLM holding facilities.  They are being housed in three 30-acre pastures and will be together during the next five breeding seasons.  Foals that are born during the study will be offered for adoption each fall after they have been weaned.  At the conclusion of the study, all adult horses
will be returned to the BLM’s Adopt-A-Horse Program or placed in long-term pasture facilities.
The BLM has an interagency agreement with the USGS for research and scientific support, and this study is a collaborative effort with scientists from the USGS, veterinarians with the Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS), and TerraMar Environmental Research LLC.

Crooks and Liars: Nevada Agriculture Director Scuttles Birth Control Study October 17, 2008

SpayVac® Immunocontraception in Feral Horses


Q – Why doesn’t BLM consider other fertility control agents such as SpayVac or Gonacon?
A – GonaCon™ is an experimental fertility control vaccine. Presently, applications of GnRH are being researched in controlled field studies for potential use as a wildlife management tool for deer. Tests of the GnRH vaccine are ongoing in several states and countries, involving a wide range of wildlife and feral species, including horses. At present, the effectiveness of GonaCon™ as a fertility control agent appears similar to or less than PZP-22 which BLM is currently using, suggesting limited potential for development of an effective longer-lasting fertility control agent.
SpayVac™ is an experimental fertility control vaccine using PZPantigens. A single vaccination with SpayVac™ has maintained a high level of contraception throughout the 4-year Nevada estray horse study. There is no regulatory approval for the management or investigational use of SpayVac™ through EPA or FDA. There is no SpayVac™ available for investigational use and no one is currently making it. Data is not available that describes the impact of SpayVac™ on the behavior and physical health of the mares. SpayVac™ may have potential for use as an effective, longer-lasting fertility control agent in the future. It may also offer an alternative to spaying mares in the future. However, additional research over the next 5-10 years would be needed before it could be used on a population-management basis. 

Evaluation of Three Contraceptive Approaches for Population Control in Wild Horses (pdf)

WILD HORSE BIRTH CONTROL WITH PZP from Dianne Nelson of The Wild Horse Sanctuary, Shingletown, CA

A Similar Vaccine, American Herds Blog Post, October 02, 2010


14 Responses to “SpayVac Fertility Control Study Begins at Pauls Valley, OK”

  1. Linda H said

    What dosage are they applying? 1 year, 2 years, 4 years? It seems to me that 10 years is a more advantageious time for the study to get good end result research of this drug. How many mares are permanently sterile and at what age is the optimum time for efficacy to keep mares fertile when the drug wears off, ect. How are the social dynamics disturbed by mares constantly cycling–compared to a control gorup? There are all questions that are unanswered and we would all like some real research from USGS.

  2. Jan said

    why does blm still use that 20 percent growth rate of herds – according to most horse biologists and people who know that percentage rate is way too high – think blm needs to get accurate counting of wild horses in the wild to see if it really is 20 percent

  3. Donna Buscemi said

    Why does BLM still call them feral when equine fossils have been found in many Western US locations proving that horses are native to America????????????

    • Fossils or not, most of the Mustangs in the American West living wild are in fact “feral” due to the fact that most were brought in by the American settlers 200 or so years ago. What wasn’t brought in by them were brought in by the Conquistadors and/or Native Americans. Yes, there are fossils of the horse in every stage of evolution on the North American continent. No, the modern Mustang of today is not a LIVE line descendant because at one point in history the entire species of Equus living in North America died. Yes they are native, and yes they are reintroduced.
      This is why I’ve never gotten the argument of feral vs. wild based on the fossils.

      • Shirleyvh said

        As I understand it, they did not all die. Many crossed the land bridge that connected this land to what we now consider to be Russia, and then onward. There has been DNA proof that many Mustangs carry the DNA of these horses that are now considered “SPanish”
        So the link goes back and forth.

        • Agreed. However, my own humble theory (for whatever its worth LOL) is that those who crossed the land bridge did so in retreat from whatever it was that caused the mass dying of those left on the North American continent. By doing so, those members of the species accomplished the ultimate goal of evolution: survival.
          There has been much speculation in the science world as to what caused the demise of the North American “Mustang” of many centuries ago, everything from mass disease resultant of a mutated strain of bacteria to asteriod impaction. Bottom line is that those who remained here did not remain for long.

          • sandra said

            There was a die off of most species at the time..most likely climate change.. similar to what is going on in texas only then it was the cold end of the spectrum..LOL..we have geological finds here of sabertooth tigers as big as a house..along with palm trees and tropical fauna in is now desert and juniper

      • sandra said

        They did not die off but migrated across the land bridge to asia, there were a million horses in texas alone that were wild horses before texas was a state..they were not turned loose by settlers

        • sandra said

          people did not turn their horses loose back in those days..horses were a necessity not a luxury….while people turned horses out to breed and some escaped to the wild herds..the wild horses had been breeding for hundreds of years to amass the totals that were said to exist in the west when settling began to take off..and at that time there were wolves and big cats aplenty to contend with

    • That’s why they’re REintroduced, not introduced.

  4. Marybeth Devlin said

    BLM recently announced immediate plans to inoculate virtually all female mustangs one year old and up that are captured then released with the Porcine Zona Pellucida (PZP-22) fertility control drug. Please note: This mass application of PZP is being undertaken concurrently with the subject five-year study. BLM has it backwards, no? Isn’t the proper order: study, then implement based on findings? This inverted approach is sure to result in mass sterilizations based on what is already known about PZP.

    First, PZP is classified as a biohazard while GonaCon is not. Surely such a fact points to GonaCon as the preferred agent. Second, PZP is classified as a sterilant — not merely a temporary contraceptive — while GonaCon is reversible. PZP’s use is predicated on the concept of every female mustang making her “genetic contribution” via one foal and then being shut down. Thus, mares would foal when it was their “turn.” In theory, each filly would be inoculated with PZP to keep her from foaling at too young an age, then not inoculated until she produced that one foal, and then sterilized through repeated administrations of PZP. If only it worked that way in practice. In fact, fillies under two years old can become sterilized after the initial injection and never recover their fertility. BLM’s plan to inoculate all fillies from the age of one year increases the odds of sterilizing most of them. Moreover, if fillies or mares are in excellent health and condition at the time they are treated, PZP can cause too strong an immune response, resulting in long delays in restoring fertility or outright sterilization after even the initial injection. Ironically, PZP works less well in fillies and mares that are in ill health or poor condition — they are likely to conceive despite PZP treatment. Thus, the fittest don’t reproduce while the least fit ones — the immuno-compromised — may, raising the possibility of selecting for immuno-compromised individuals. For these reasons, much care must be taken when administering PZP. Again, it should not be given to fillies under two years old and never administered for four years consecutively, but the announced plan would do both. I concede that, as an alternative to euthanasia or slaughter, sterilization is preferable. However, wild horse advocates may wish to see self-sustaining mustang herds live on. BLM’s plan will eventually exterminate the herds.

    The superior solution for preventing an overpopulation of wild horses — while still having viable herds — is to re-introduce apex predators to the range from which they were deliberately exterminated. The next step is to restore the millions of acres of herd areas from which BLM has improperly barred mustangs. A stop-gap measure would be fertility control using a reversible agent such as GonaCon, which has fewer side effects than PZP.

    • MaryBeth,
      During research on this subject, we came across an article in one of the online newspapers where your comments were quite interesting, mainly because of the amount of actual science behind them. We would be very interested in some of your research findings if you would like to share.

  5. LisaN. said

    Why is $41 million dollars of hard earned tax dollars being used for fertility control on an endangered species? 20% population growth rate is not scientific (pryor mt. herd had zero growth rate last year) and numbers left in the wild are at critically low levels (way below safe number for genetic viability). There are less than 10,000 wild equines left in over 10 states. Why don’t you just admit you’re exterminating the species period. When they are gone you can expect higher & more rapid rate of dessertification and catastrophic wild fires. Then what will those 7 million cattle eat & drink?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: