#Pesticide PZP is dangerous for the last American herds of wild horses and burros

PM PZP Injection

The old hypothesis — that PZP merely blocks sperm attachment — has been disproved.

Kaur & Prabha (2014) found that the infertility brought on by PZP is ” … a consequence of ovarian dystrophy rather than inhibition of sperm-oocyte interaction.” They reported that PZP’s antibodies induce ovarian dystrophy, oophoritis (inflammation of the ovaries), destruction of oocytes in all growing follicles, and depletion of resting follicles.

Despite all the hype about PZP being non-hormonal, the manufacturer himself knew that it had an adverse hormonal effect — significantly-lowered estrogen. In 1992, he reported that ” … three consecutive years of PZP treatment may interfere with normal ovarian function as shown by markedly depressed oestrogen secretion.” Thus, PZP is an endocrine disruptor.

Worse yet, Sacco et al. (1981) found that PZP antibodies are transferred from mother to young via the placenta and milk. The transferred antibodies cross-react with and bind to the zonae pellucidae of female offspring. This is bad news because BLM regularly administers PZP to pregnant and lactating mares, who transfer the destructive antibodies to their filly-foals. Thus, the fillies get their first treatment with PZP in utero, while nursing, or both.

Nettles (1997) found an association between PZP and stillbirths. In 2015, the International Society for the Protection of Mustangs and Burros reported that 7 mares previously treated with PZP, when taken off it, were able to get pregnant. However, 6 of those 7 mares — that is, 86 percent — produced foals that were stillborn. All other ISPMB mares that had not been previously injected with PZP successfully birthed healthy foals. Environmental and other conditions were identical. The only variable was PZP. Meanwhile, over on the East Coast, the Corolla herd, long-managed with PZP, has recently experienced birth defects among its newborns.

Gray & Cameron (2010) questioned the supposed benefit of PZP-sterilized mares living much longer than their normal life expectancy, and and Knight & Rubenstein (2014) warned of unintended consequences of PZP’s ironic effect of extended longevity. Ultra-elderly mares take up scarce slots within AML-restricted herds. They consume resources but no longer contribute to the gene-pool. It is detrimental to a population’s genetic viability to carry significant numbers of sterile herd-members way-beyond their normal life-span. Meanwhile, those few foals that are born have to be removed to achieve AML because they’re more adoptable.

Ransom et al. (2013) conducted a longitudinal study of three herds currently being managed by PZP — Little Book Cliffs, McCullough Peaks, and Pryor Mountain. They found that the the birthing season lasted 341 days — nearly year-round — which puts the life of mares and foals in jeopardy. Nature designed the equine birthing-season to occur in Spring, not year-round, and certainly not in the dead of Winter.

Ransom et al. also found that, after suspension of PZP, there was a delay lasting 411.3 days (1.13 years) per each year-of-treatment before mares recovered their fertility. They warned: “Humans are increasingly attempting to manage the planet’s wildlife and habitats with new tools that are often not fully understood. The transient nature of the immunocontraceptive PZP can manifest into extraordinary persistence of infertility with repeated vaccinations, and ultimately can alter birth phenology in horses. This persistence may be of benefit for managing overabundant wildlife, but also suggests caution for use in small refugia or breeding facilities maintained for repatriation of rare species.”

PZP’s manufacturer conceded that it could take up to eight years to recover fertility after just three consecutive PZP treatments.

The study on PZP by Knight & Rubenstein (2014) found that ” … three or more consecutive years of treatment or administration of the first dose before sexual maturity may have triggered infertility in some mares.” These findings are particularly troubling. They suggest that, actually, only two consecutive PZP-treatments may be reversible. Except, that is, in the case of fillies who have not yet reached puberty — they could be sterilized by just one injection.

PZP’s manufacturer was quoted describing PZP as “so safe it is boring.” Independent research shows otherwise — that PZP is a powerful hormone disruptor that could sterilize a female with just one injection. If staff and volunteers believe that PZP is boringly safe, they will be less likely to protect themselves adequately from this dangerous pesticide. Indeed, many of the volunteers are women and, therefore, at risk. Accidental self-injection with PZP could cause them to suffer diseased ovaries and depressed estrogen-levels — in addition to infertility and, potentially, sterility. Consider the magnitude of the risk — the PZP-in-question is a horse-size dose.

~ Marybeth Devlin, Wild Horse Advocate

Protect Mustangs is an organization who protects and preserves native and wild horses.

Native wild horses are not pests ~ Stop managing them to extinction

Dear Friends of Wild Horses and Burros

Protect Mustangs is a national nonprofit organization making grassroots count. Our mission is to protect and preserve native and wild horses. Besides engaging mostly in outreach and education about the wild horse crisis, we advocate for holistic land management, self-sustaining herds and reserve design. We are calling for a 10 year moratorium on roundups for the herds to recover from the roundups and for studies to form good management plans. Right now there are no accurate census counts on the range so we don’t even have a clear picture of the few wild horses left living in freedom.

Our members don’t see an overpopulation or “excess” of wild horses on public land, even if the population is over BLM’s biased appropriate management level (AML). Livestock outnumbers wild horses more than 50 to 1 on the range. Yet wild horses are always scapegoated for damage by special interest groups.

We are deeply concerned that the use of FDA approved “restricted use pesticides” such as PZP–an immunocontraceptive made from pig ovaries that people call birth control–sterilizes mares after multiple uses and should never be used on nonviable herds, those herds with less than 150 wild horses. Genetic diversity is essential for survival and using PZP surely will curtail that. There is one herd in Nevada currently being treated by wild horse advocates that seems to have less than 50 wild horses. This worried us.

Wild horses are a native species and not pests. Sadly there are factions who are treating wild horses as individuals and ignoring the herd element and other factions treating wild horses as invasive pests.

Despite decades of experimental research on wild mares, the FDA would not approve PZP as safe. Eventually the EPA approved it as a restricted use pesticide. You can see the pesticide fact sheet here: http://www.epa.gov/pesticides/chem_search/reg_actions/pending/fs_PC-176603_01-Jan-12.pdf

How can drugging mares with restricted use pesticides be honoring their freedom? Most of the time the BLM will need to round them up to dart them anyway. You can hear the BLM official speak about that here: http://www.thespectrum.com/videos/news/local/cedar-city/2014/08/06/13698391/

We are also concerned PZP and other sterilants affect behavior and that mares will be subjected to live in unnatural situations.

Ruining survival of the fittest and natural selection is our biggest concern if man chooses who breeds and how many foals are born. The herds must adapt to upcoming environmental and climate changes in order to survive, therefore genetic variability is essential at this pivotal time.

You can read about PZP on these various posts: http://protectmustangs.org/?s=PZP+&submit=Search

Here you can read about Gonacon on these posts: http://protectmustangs.org/?s=gonacon&submit=Search

This is also a good post to read about the ISPMB and Princeton study that shows wild horse herds with functional social structures contribute to low herd growth compared to BLM managed herds: http://protectmustangs.org/?p=6057

You can search other topics you might have questions about in our search bar too: http://protectmustangs.org

We are 100% volunteer and are working to help the wild horses without any conflict of interest as far as we can tell. We do not receive funding from influencers, corporations or organizations connected with the drug PZP, the pharmaceutical industry, Big Oil and Gas or other energy, ranching and mining sources. That’s why your donations are so important.

Our vision is to speak out for the voiceless, stop the BLM from being cruel to wild horses and work towards a solution for healthy management keeping wild horses on the range based on good science. We have a petition out for the 10 year moratorium on all roundups. Please sign and share it here: http://www.change.org/petitions/sally-jewell-urgent-grant-a-10-year-moratorium-on-wild-horse-roundups-for-recovery-and-studies

Thank you for reaching out to us. It’s important to do the research and find the answer for yourself so you can feel good about taking action to help save the last of the wild horses and burros.

We are grateful you care so deeply about saving America’s wild ones.

Many blessings,


Anne Novak
Executive Director
Protect Mustangs
San Francisco, California

Read about native wild horses: http://protectmustangs.org/?page_id=562

Twitter: https://twitter.com/TheAnneNovak
Facebook: https://www.facebook.com/ProtectMustangs
In the news: http://protectmustangs.org/?page_id=218

Protect Mustangs is a national nonprofit organization who protects and preserves native and wild horses.