Who are the traitors in wild horse advocacy?

Who is exploiting wild horses now? 

CLUE: FOIA the contracts, the agreements and their emails with BLM

Do you realize who has betrayed America’s wild horses? Do you know who is who? Do you know who are the BLM supporters and partners now? Do you know who is pretending to work for “solutions” but is really working for the livestock industry? Do you know who is making back-room deals pushing pesticides for birth control, experiments and slaughter on underpopulated wild horses and burros?

Do you know who is really for the wild horses and burros now?

FACT SHEET: The Truth about PZP

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PZP — The Pesticide

Porcine zona pellucida (PZP aka ZonaStat-H or Native PZP) is an EPA-registered pesticide derived from the ovaries of slaughtered pigs. PZP is approved for use on wild horses “in areas where they have become a nuisance ….” [20]

Some persons argue that, because PZP does not kill the mare, it is not really a “pesticide.” Actually, PZP does kill. As will be documented in this report, its use is associated with stillborn foals. In the long term, PZP will weaken a herd immunologically, which could swiftly lead to its extinction. So, yes, PZP is a real pesticide.

PZP — an Anti-Vaccine

While touted as a “vaccine,” PZP is actually a perversion of what a true vaccine is supposed to be. Instead of preventing disease, PZP causes disease — auto-immune disease. Thus, PZP is an anti-vaccine.

PZP’s Mode of Action as Stated in the Pesticide Registration Is a Disproved Hypothesis

The registrant of PZP advised the Environmental Protection Agency (EPA) that, based on information from the pesticide’s researcher-manufacturer, PZP works by generating antibodies that “block sperm attachment.” This representation of PZP as a sort of chemical condom was not fact but merely an untested hypothesis, postulated three decades ago. The old hypothesis was disproved by subsequent research. PZP’s manufacturer knew, or should have known, this. The manufacturer should also have been informed and up-to-date regarding the side effects and unintended consequences of PZP. Yet, the manufacturer continued to cite the disproved hypothesis and to deny that PZP has any adverse effects. [7 and 13]

PZP’s True Mode-of-Action

So how does PZP really work? PZP tricks the immune system into waging war on the ovaries. In a meta-analysis of ZP-type contraceptives, Kaur & Prabha (2014) reported that the infertility brought on by such products is ” … a consequence of ovarian dystrophy rather than inhibition of sperm-oocyte interaction.” Thus, PZP’s antibodies “work” not by blocking sperm attachment but by destroying the ovaries. Kaur & Prabha further disclosed that ” … histological examination of ovaries of immunized animals revealed the presence of atretic follicles with degenerating oocytes.” [5] [Atretic follicles are ovarian follicles in an undeveloped state due to immaturity, poor nutrition or systemic disease; manifested by prolonged anestrus.]

Kaur & Prabha’s review concluded that PZP’s antibodies induce ovarian dystrophy, oophoritis (inflammation of the ovaries), destruction of oocytes in all growing follicles, and depletion of resting follicles. The manufacturer of PZP as well as Bureau of Land Management (BLM) should have been aware of these and other findings about the pesticide. Yet they ignored or disregarded any information that was contrary to their personally-preferred but obsolete and false description of PZP’s mode-of-action.

PZP Manufacturer’s Own Research Found Markedly Depressed Estrogen Secretion

In a telling study published back in 1992, the manufacturer of Native PZP, along with colleagues, reported that ” … three consecutive years of PZP treatment may interfere with normal ovarian function as shown by markedly depressed oestrogen secretion.” [6] Thus, despite all the hype about PZP being non-hormonal, the manufacturer knew that ZonaStat-H has an adverse hormonal effect, causing significantly-lowered estrogen. Thus, PZP is an endocrine disruptor. [21] The plummeting estrogen-levels may also reflect the ovarian dystrophy and oophoritis now known to be caused by PZP. Despite personally discovering negative hormonal impacts 23 years ago, PZP’s manufacturer continued to cite misinformation regarding the product’s mode-of-action and endocrine-disruptor side-effects.

PZP Causes Ovarian Cysts

In their 2010 meta-analysis, Gray & Cameron cited a number of studies that found ” … alterations to ovarian function, oophoritis, and cyst formation with PZP treatment (Mahi-Brown et al.1988, Sehgal et al. 1989, Rhim et al. 1992, Stoops et al. 2006, Curtis et al. 2007).” [4] These findings support those of Kaur & Prabha while introducing yet another adverse effect: ovarian cysts. Gray & Cameron’s review also noted that increased irritability, aggression, and masculine behavior had been observed in females following PZP-treatment.

PZP → Endocrine Disruptor → Elevated Testosterone → Masculinizing Effects

Recall that PZP has endocrine-disrupting effects that result in lowered estrogen. Per the observed masculine behavior of treated mares, PZP seems to have a testosterone-elevating effect too. A deficit of estrogen alone would not necessarily manifest in the masculinization of treated females, but an excess of testosterone would. So, it appears that PZP disrupts at least two hormones: estrogen — by substantially lowering it — and testosterone — by substantially elevating it. Adverse effect: Unnatural behavior.

PZP → Ovarian Cysts → Elevated Testosterone → Masculinizing Effects

As discussed above, PZP correlates with abnormal masculine behavior on the part of treated females, a side-effect likely due to elevated testosterone. But in addition to the endocrine-disruption caused by PZP, there could be a second way for testosterone levels to become elevated. Recall that PZP causes ovarian cysts. An Internet search on “ovarian cysts and testosterone” yielded results for polycystic ovary syndrome (PCOS) in women. Interestingly, one of the symptoms of PCOS is high testosterone levels. [12 and 22] The connection between ovarian cysts and elevated testosterone suggests that the ovarian cysts caused by PZP could — either alone or in combination with PZP’s endocrine-disruptor effects — lead to high testosterone levels in treated females, as evidenced by their masculinized behavior.

PZP Causes Additional Adverse Effects

Gray & Cameron’s review also disclosed that, when PZP was administered to the females of a herd, males lost body condition while the oft-claimed improvement in female body condition did not hold up. Further, mares remained sexually active beyond the normal breeding season and had more estrus events.

PZP Selects for Weak Immune Function

Gray & Cameron’s analysis raised the possibility of PZP selecting for immuno-compromised individuals. Here’s why. Because PZP stimulates the immune system, it ironically works “best” — sterilizes faster — in mares that have strong immune-function. Such mares respond to the anti-vaccine and produce quantities of PZP antibodies that destroy their ovaries. But, conversely, PZP may not work at all in mares whose immune-function is weak or depressed. Those mares fail to respond to PZP. They keep getting pregnant and producing foals who, like their dam, suffer from weak immune-function. So, the PZP pesticide works against the very horses that Nature has best equipped for survival against disease while favoring and selecting for the immuno-compromised. Thus, a herd being treated with PZP is undergoing selective breeding for weak immunity, which puts the population at risk for disease — and ultimately, for extinction.

PZP Confers Dubious “Benefit” of Increased Longevity

Gray & Cameron also cited a study that found that “… PZP treated feral horse mares lived longer, resulting in a new age class (>25 years) not present before treatment ….” Exceptionally-long life is an ironic effect of PZP treatments. PZP’s manufacturer actually boasts about it, as if the anomaly were a good thing. However, Gray & Cameron questioned the supposed benefit of mares living much longer than their normal life expectancy. Indeed, such mares take up scarce slots within size-restricted populations. The ultra-elderly mares continue to consume resources for many years, but they 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.

Research on Wildlife Contraceptives Revealed Stillbirths and Auto-Immune Oophoritis from PZP

There was an even earlier, definitive meta-analysis on wildlife contraceptives. Nettles (1997) reviewed 75 studies available at that time on the subject. Among his findings regarding PZP-use across different species, including horses, were: Stillbirths; altered ovarian structure and cyclicity; interference with normal ovarian function; permanent ovarian damage; and some cases of irreversible sterility due to auto-immune oophoritis, which suggested that PZP can be selective against a certain genotype in a population. [10] Many of these findings were confirmed by Kaur & Prabha as well as by Gray & Cameron. Please keep in mind these key findings: Stillbirths, and auto-immune oophoritis.

Recent Stillbirths Correlated with PZP

There is recent evidence confirming Nettles’ finding of a correlation between PZP treatments and subsequent stillbirths. In June 2015, Karen Sussman, President of the International Society for the Protection of Mustangs and Burros, reported that 7 mares previously treated with PZP at ISPMB, when taken off PZP, 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 injected with PZP successfully birthed healthy foals. Thus, given that environmental and other conditions were identical, the only variable was PZP. The dead foals have been sent to a university pathology department for autopsy. [18]

Autoimmune Oophoritis Induced by PZP

Research by the Rose-Cihakova-Caturegli Laboratory at Johns Hopkins Pathology found: “Automimmune oophoritis can be induced by immunization with testis and ovarian antigen murine human zona pellucida 3 peptide (pZP3) in adjuvant.” [16] Here again, is causation of autoimmune disease by a ZP-type product. This finding confirms other research cited herein.

Autoimmune Oophoritis and Risk of Other Autoimmune Diseases

A study by Varras et al. disclosed that, in humans, autoimmune oophoritis carries the risk of the patient developing other autoimmune diseases. [23] The correlation between autoimmune oophoritis and subsequent other autoimmune disorders weighs against injecting fillies and mares with PZP repeatedly and en masse.

Prolonged Breeding Season, Unusually-late Parturition Dates with PZP

Nettles’ meta-analysis on PZP disclosed other adverse effects: A prolonged breeding season and unusually-late parturition dates. (Parturition is the formal term for “giving birth.”) These findings have recently been confirmed, as is discussed below.

Parturition-Season Extends to Nearly Year-Round When a Herd Is Treated with PZP

A longitudinal study (Ransom et al. 2013) of three herds currently being managed by PZP — Little Book Cliffs, McCullough Peaks, and Pryor Mountain — found that the the parturition season lasted 341 days. [15] Ransom et al.’s finding of a nearly year-round birthing season supports the earlier finding by Nettles. Thus, during its period of potential reversibility, PZP’s effects wear off unpredictably. Out-of-season births put the life of both the mare and the foal in jeopardy. Nature designed the equine birthing-season to occur in Spring, not year-round, and certainly not in the dead of Winter.

Prolonged Delay in Recovery of Fertility

The same longitudinal study by Ransom et al. 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. What this means is that it takes that long, on average, for the ovaries to heal, to clear out all those cysts, and to regain some degree of normal hormonal function.

The question is: How is the delay in recovery-of-fertility addressed by BLM management practices? Answer: BLM ignores it. For instance, BLM currently administers PZP to Pryor Mountain’s fillies and mares starting at age 1½ — whom BLM artfully describes in the Environmental Assessment as fillies “becoming two year olds” — through age four. Thus, these fillies and mares receive intentional treatments for four consecutive years before being allowed the privilege of reproductive potentiality. Per Ransom et al.’s study, the Pryor Mountain fillies and mares would be expected to need 1,645.2 days (4.51 years) to regain reproductive capacity. But BLM gives the Pryor Mountain mares only 5 years off PZP before they are put back on it again — for the rest of their life. Thus, these fillies and mares might have just a six-month window — at best — in which to conceive. Due to the unpredictable timing of PZP’s wearing off, for some mares that window of fertility will close before they get a chance to produce a foal. Those mares’ genetic contribution will be zero.

As if the above scenario were not bad enough, PZP’s manufacturer conceded that it could take up to eight years to recover fertility after just three consecutive PZP treatments. [13]

Ransom Advises Proceeding with Caution regarding PZP

The Ransom et al. study 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.” [15]

Because BLM keeps over 70 percent of the herds at levels below minimum-viable population (MVP), most herds qualify as “small refugia.” Pryor Mountain WHR is a small, isolated refuge, and its wild horses carry genes with rare alleles.

Ransom’s Exclusion of Seven Mares Evidences PZP’s Non-Effect on Immunocompromised Mares

In the “Data Collection” methodology section of the Ransom et al. report, the authors advised: “We omitted data for one female from the Little Book Cliffs and six females from McCullough Peaks because they produced offspring in every treatment year and thus were never effectively contracepted.”

This fact is important because it evidences PZP’s lack-of-efficacy on immunocompromised fillies and mares. To review: Because PZP activates the immune system, mares with naturally-low or depressed immune function do not “respond” to the treatment. It’s as if they had been injected with saline — their immune system is so weak that it does not react to the PZP by producing antibodies. The good news is such mares’ ovaries are saved from PZP’s destructive effects. The bad news is that these mares continue to become pregnant year after year, producing foals that will also tend to inherit low immune-function. Over time, the herd will become populated with more such low-immune horses because those with strong immunity get sterilized. Thus, PZP selects for horses with low immune function, which is bad for a herd in the long term. Even a routine infection could spread quickly and wipe out a population of horses with weak immune-function. If the goal is to preserve a herd, the use of PZP constitutes a worst management-practice.

BLM Was Fully-Aware of the Ransom Study but Suppressed the Findings

In their report, the authors of the Ransom et al. study gave a shout-out to BLM “for administrative and technical support throughout this project.” Thus, BLM was fully aware of the multi-year study while it was in progress and even lent support to it administratively and technically. Yet, in the case of the Pryor Mountain herd, BLM omitted this important report as a reference for the 2015 Environmental Assessment, which proposed intensifying the PZP “prescription.” Thus, BLM pretended that there was no such report and unethicallly suppressed it. Consequently, the public could not comment knowledgeably and appropriately on the continued use of — let alone the accelerated application of — PZP.

Three PZP Injections Can Trigger Sterility in Mares, or Just One Shot in Fillies Before Puberty

Disturbingly, another recent study on PZP (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. [9]

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. Recall the Pryor Mountain fillies, whose PZP treatments begin when they are just 1½ years old. They may not have reached puberty when they are initially treated. [1] And as we shall see later in this report, that first shot of PZP may not be their first shot of PZP.

Researchers Again Express Concerns about the Abnormal Life-Spans of Sterilized Mares

Knight & Rubenstein warned: “Inducing sterility, while relieving the mares from the energetic costs of lactation and reducing the stress from harem switching, may have unintended consequences on population dynamics by increasing longevity and eliminating the mares’ ability to contribute genetically.”

Knight & Rubenstein’s concerns support those of Gray & Cameron, who also questioned the supposed benefit of sterile mares’ extended life-spans. The abnormal numbers of aged, sterile mares count for census-purposes; but their presence disadvantages the younger horses, who become tageted for removal in order for BLM to achieve arbitrary management levels. Further, such mares no longer belong to the viable gene-pool.

PZP’s Destructive Antibodies Are Transmitted via the Placenta and Mother’s Milk

It gets worse. Sacco et al. reported that, per radioimmunoassay, 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, as demonstrated by immunofluorescent techniques. [17] These findings were disclosed in 1981. PZP’s manufacturer must have known about this dangerous effect, and certainly BLM should have investigated on its own whether there was any risk to the unborn or the nursing foal. Yet, the manufacturer continued to insist that there was no danger to the foal, whether born or unborn. [7 and 13] And in fact, BLM regularly administers PZP to pregnant and lactating mares, who transfer the destructive antibodies to their fetus, via the placenta, and to their foal, via mother’s milk.

Recall again the Pryor Mountain fillies. If their dams were injected with PZP while pregnant or nursing, such fillies will already have PZP antibodies cross-reacted with and bound to their zonae. Therefore, when those same fillies are injected at age 1½, it will be their second treatment, or potentially even their third. In fact, they could already have been sterilized in utero or while nursing, the treatment having been received prior to puberty, about which Knight & Rubenstein warned.

PZP Weakens Herd-Immunity, Posing Risk of Stochastic Events Leading to Herd-Extinction

To be self-sustaining, a herd needs to possess good immunity to withstand random catastrophes — known as stochastic events — such as contagious infections. There was such an event recently in Kazakhstan, where 120,000 endangered Saiga antelope — half the world’s population — died off suddenly and inexplicably within a two-week period. Scientists think a common bacterial infection was the cause of this mass-mortality event, but are unsure why the antelope were unable to fight off the disease immunologically. [14]

Imagine if such a catastrophe were to befall the Pryor Mountain horses, whose herd-immunity is being eroded by PZP. Note that the Saiga deaths involved antelope-mothers and their calves. If Pryor Mountain’s few fertile mares and their foals perished all of a sudden, that would leave just stallions and sterile old mares. The herd would be composed of the living dead, reproductively speaking, its rare alleles extinguished. BLM is failing to proactively manage the Pryor Mountain herd with stochastic events taken into consideration. That is malfeasance. PZP is a tool of immunological destruction, not of proper management.

PZP Continues the Use of Roundups and Removals

If the promise of PZP were true — if PZP really did eliminate the need to remove “excess” wild horses from the range — removals would have ended long ago in the Pryor Mountain Wild Horse Range, where PZP has been in use for approximately two decades. Yet removals are scheduled there with regularity every three years, the latest one in 2015.

Risks to Humans Who Administer PZP Injections

For staff and volunteers who inject wild horses with PZP, EPA’s Pesticide Fact Sheet advises that Personal Protective Equipment requirements include long sleeved shirt and long pants, gloves and shoes plus socks to mitigate occupational exposure. EPA specifically warns that pregnant women must not be involved in handling or injecting ZonaStat-H, and that all women should be aware that accidental self-injection may cause infertility. [20]

However, EPA’s Fact Sheet, the manufacturer’s training, and BLM’s operating procedures fail to inform pregnant women why it is so important that they strictly avoid PZP — because PZP’s antibodies cross the placenta and cross-react with and bind to an unborn female child’s own little zonae pellucidae. The baby-girl could be “anti-vaccinated” with PZP and even sterilized before birth.

EPA’s Fact Sheet, the manufacturer’s training, and BLM’s operating procedures fail to warn lactating women to avoid PZP and why — because PZP’s destructive antibodies would be passed along to a nursing female child via mother’s milk. The baby-girl could be “anti-vaccinated” with PZP and possibly sterilized simply from nursing.

EPA’s Fact Sheet, the manufacturer’s training, and BLM’s operating procedures fail to warn all women of the risk of ovarian dystrophy, oophoritis, ovarian cysts, and elevated testosterone-levels — in addition to infertility and, potentially, sterility — from unintentional self-injection.

EPA’s Fact Sheet, the manufacturer’s training, and BLM’s operating procedures fail to emphasize the magnitude of the risk — the PZP-in-question is a horse-size dose.

But Is There a Mandate to Practice Scientific Integrity?

Yes. The Department of the Interior’s (DOI) Code of Scientific and Scholarly Conduct applies to all staff members as well as to contractors, partners, permittees, and volunteers. The Code states: “Scholarly information considered in Departmental decision making must be robust, of the highest quality, and the result of as rigorous scientific and scholarly processes as can be achieved. Most importantly, it must be trustworthy.” [19]

BLM has ignored and suppressed independent scientific findings about PZP’s adverse effects and unintended consequences. Instead, BLM continues to rely almost exclusively on the manufacturer’s claims — shown and known to be false — regarding PZP’s safety for use on horses and for handling by humans. BLM is thus non-compliant with the Policy and malfeasant in its responsibilities to protect staff, volunteers, and the wild horses under its jurisdiction. BLM is also misleading and disinforming Congress and the American public about the PZP pesticide.

The manufacturer of PZP — a partner to BLM — misrepresented the pesticide as safe for use on animals by humans. The manufacturer knew or should have known that the former hypothesis regarding PZP’s mode-of-action had been disproved, and that PZP has dangerous side effects, safety-issues, and unintended consequences. Yet he hid and denied that information and failed to warn about PZP’s adverse effects. The manufacturer cited his own research as if it were definitive, and aggressively criticized independent researchers whose findings did not fully support his claims. Indeed, he recently submitted an Op-ed to The Salt Lake Tribune wherein he belittled the research of fellow scientists whose studies on PZP yielded results somewhat different from his own. [8] His accusations were so unreasonable that the scientists felt it necessary to submit an Op-ed in response to defend the integrity and validity of their work. [11] The manufacturer also disparaged members of the public — one of whom was a member of the Pennsylvania Game Commission — who expressed concerns about PZP. He dismissively accused them of “an attempt to mislead,” of “hyperbole,” of “knowingly manipulating information,” of “attempts to frighten people,” and of indulging in an “anti-intellectual approach to debates.” [7] By these actions, the manufacturer violated the DOI’s Code of Scientific and Scholarly Conduct.

PZP Manufacturer Misled Trainees into Believing that PZP Was Safe

BLM staff and volunteers receive their training from PZP’s manufacturer in how to handle and administer the pesticide. BLM is remiss in delegating the training to the manufacturer without verifying the adequacy of the instruction and the truthfulness of it. Two comments recorded recently in the media suggest that PZP’s manufacturer misled not just the public-at-large but those who received training therefrom in how to administer PZP.

First, the manufacturer has been quoted as saying that PZP is “so safe it is boring.” [3] Independent research shows otherwise — that PZP is a powerful hormone disruptor that could sterilize a female with just one injection. If trainees believe that PZP is boringly safe, they will be less likely to protect themselves adequately from this dangerous pesticide. Indeed, many of the trainees are women and, therefore, particularly at risk. Likewise, wild-horse advocates are lulled into complacency, trusting that PZP is harmless to the Pryor Mountain horses and their rare genetic alleles. Of course, none of that is true.

Second, a PZP supporter, who self-identified as a recent completer of the PZP-darting training program conducted by the manufacturer, said in a comment posted to a news article: “I just received my FDA certification to handle and administer Native PZP. Would you be so kind to provide a link to the study you keep referencing? To my knowledge, and those teaching the Native PZP certification class, there are no side effects of the PZP produced by Dr. Kirkpatrick and his team, which is Native PZP.” [2] Key words: “no side effects.” It is disturbing that a person who was, no doubt, motivated by a desire to help the horses has been disinformed regarding PZP’s safety-hazards to humans as well as to horses.

BLM Fails to Maintain Proper Supervision of the PZP Volunteers

The issue of safety is not the only concern. As BLM has admitted, volunteers darted the wrong mares on Pryor Mountain. These errors evidence that BLM has failed to maintain supervisory control over the volunteer-inoculators, allowing them to conduct the PZP-darting by themselves. The mistakes further evidence that the volunteers do not understand what is expected of them. Who can say whether other procedures were not complied with either. The fact that mares were darted who were ineligible for PZP per the then-current protocol, but who would be eligible under the proposed-but-not-yet-promulgated new “prescription,” suggests that the volunteers may have concluded — from BLM’s open contempt for the Constitution and disrespect for the NEPA process — that was okay for them to start darting otherwise-ineligible mares right away. Not surprisingly, BLM blames the volunteers for these mistakes, but probably has not informed them that they are being made to take the rap for management’s shortcomings.


PZP is appropriately categorized as a pesticide by the EPA. PZP “works” by tricking the immune system into attacking and destroying the ovaries. PZP has many adverse effects as well as unintended consequences. PZP presents safety-hazards to humans who handle it. PZP is a dangerous pesticide whose use is antithetical to the spirit and intent of the Wild and Free-Roaming Horses and Burros Act. BLM’s continuing to use PZP while ignoring and suppressing the evidence of its harmful effects constitutes malfeasance.


This report was completed by Marybeth Devlin on December 24, 2015. Copyright Marybeth Devlin and Protect Mustangs 2015.


1. EquiMed staff. (2010, March 13) Equine Reproductive Maturity in Mares and Stallions. Puberty in Equines. Retrieved from http://equimed.com/health-centers/reproductive-care/articles/equine-reproductive-maturity-in-mares-and-stallions

2. EWCS. (2015, November 10). Re: “Contraceptive could reduce taxpayer costs for wild horses.” Retrieved from http://wyomingpublicmedia.org/post/contraceptive-could-reduce-taxpayer-costs-wild-horses#comment-2352628323

3. Ferguson, Mike. (2015, June 4) “Police called as group protests wild horse contraceptives.” The Billings Gazette. Retrieved from http://billingsgazette.com/news/state-and-regional/montana/police-called-as-group-protests-wild-horse-contraceptives/article_81462303-e128-5ee8-a7ef-2c8b098450f6.html

4. 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. Online publication date: 1-Jan-2010. Retrieved at http://www.reproduction-online.org/content/139/1/45.full

5. Kaur, Kiranjeet and Prabha, Vijay. (2014) “Immunocontraceptives: New Approaches to Fertility Control,” BioMed Research International, vol. 2014, Article ID 868196, 15 pages, 2014. doi:10.1155/2014/868196. Retrieved from http://downloads.hindawi.com/journals/bmri/2014/868196.pdf

6. Kirkpatrick, J. F., I. K. M. Liu, J. W. Turner, Jr., R. Naugle, and R. Keiper. 1992a. Long-term effects of porcine zonae pellucidae immunocontraception on ovarian function of feral horses (Equus caballus). J. Reprod. Fert. 94:437-444. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/1317449

7. Kirkpatrick, Jay. 2007. “Response to PA [Pennsylvania] Game Commission.” Posted on PNC’s Wildlife Forever Home Page. Retrieved from http://www.pzpinfo.org/home.html

8. Kirkpatrick, Jay F. (2015, May 16). Op-ed: Wild-horse contraceptives are based on sound science. The Salt Lake Tribune. Retrieved from http://www.sltrib.com/opinion/2517266-155/op-ed-wild-horse-contraceptives-are-based-on?fullpage=1

9. Knight, Colleen M., Rubenstein, Daniel I. 2014. The Effects of Porcine Zona Pellucida Immunocontraception on Health and Behavior of Feral Horses (Equus caballus). Princeton University Thesis, Ecology and Evolutionary Biology. Retrieved from http://dataspace.princeton.edu/jspui/handle/88435/dsp01vt150j42p

10. Nettles, Victor F. (1997) Potential consequences and problems with wildlife contraceptives. Reproduction, Fertility and Development 9(1) 137 – 144. Retrieved from http://www.publish.csiro.au/paper/R96054.htm Accessed full pdf text via purchase of a copy from Csiro Publishing.

11. Nuñez, Cassandra, Jim Adelman and Dan Rubenstein. (2015, July 3). Op-ed: Wild horse contraception not without unintended consequences. The Salt Lake Tribune. Retrieved from http://www.sltrib.com/opinion/2653298-155/op-ed-wild-horse-contraception-not-without

12. PCOS Foundation. (2015) What Causes PCOS? Retrieved from http://www.pcosfoundation.org/what-is-pcos

13. PNC, Inc. (Pity Not Cruelty). PZP FAQs. (2006) “Frequently Asked Questions on Immunocontraception.” (Special thanks to Jay Kirkpatrick and Rick Naugle for additions and corrections). Retrieved from http://www.pzpinfo.org/pzp_faqs.html

14. Raab. Lauren. (2015, May 31) “120,000 endangered saiga antelopes die mysteriously in Kazakhstan.” Los Angeles Times. Retrieved from http://www.latimes.com/science/sciencenow/la-sci-sn-saiga-antelope-die-off-20150531-story.html

15. Ransom JI, Hobbs NT, Bruemmer J (2013) Contraception Can Lead to Trophic Asynchrony between Birth Pulse and Resources. PLoS ONE 8(1): e54972. doi:10.1371/journal.pone.0054972. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/23383018

16. Rose-Cihakova-Caturegli Laboratory. (n.d.) Autoimmune Oophoritis. Johns Hopkins Pathology. Retrieved from http://pathology.jhu.edu/department/RCCLab/Oophoritis.cfm

17. Sacco AG, Subramanian MG, Yurewicz EC. (1981) Passage of zona antibodies via placenta and milk following active immunization of female mice with porcine zonae pellucidae. J Reprod Immunol. 1981 Dec;3(6):313-22. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/7328557

18. Sussman, Karen. (2015 June 6) “Suspicious Deaths with Use of Anti-Fertility Drugs.” International Society for the Protection of Mustangs and Burros. Retrieved from http://www.ispmb.org/BirthControlDeaths.html

19. United States Department of the Interior. Integrity of Scientific and Scholarly Activities Policy. Code of Conduct. Retrieved from https://www.doi.gov/scientificintegrity

20. United States Environmental Protection Agency. Office of Chemical Safety and Pollution Prevention. Pesticide Fact Sheet. Porcine Zona Pellucida (PZP). New Chemical. Nonfood Use. January 2012. Retrieved from

21. U.S. Department of Health and Human Services. National Institutes of Health. Endocrine Disruptors. Retrieved from http://www.niehs.nih.gov/health/topics/agents/endocrine/

22. U.S. National Library of Medicine. National Institutes of Health. Ovarian overproduction of androgens. Retrieved from https://www.nlm.nih.gov/medlineplus/ency/article/001165.htm

23. Varras M, Anastasiadis A, Panelos J, Balassi E, Demou A, Akrivis CH. (2013) Autoimmune oophoritis: Clinical presentation of an unusual clinical entity. OA Case Reports 2013 Jan 31;2(1):7. Retrieved from http://www.oapublishinglondon.com/article/369#

Pm PZP Darts


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

Equine reproductive immunology Ph.D speaks out in 2010 against using PZP on wild horses

PM President Obama Listen to the Science

November 27, 2010

Jared Bybee, Wild Horse and Burro Specialist

Department of the Interior

Bureau of Land Management

Billings Field Office

5001 Southgate Drive

Billings, Montana 59101-4669

VIA FAX: 406-896-5281

RE: Pryor Mountain Wild Horse Range Fertility Control Preliminary Environmental
Assessment Tiered to the Pryor Mountain Wild Horse Range Environmental Assessment and Herd Management Area Plan May 2009 EA DOI-BLM-MT-0010-2011-0004-EA

Dear Jared Bybee:


I appreciate the opportunity to submit comments on the Pryor Mountain Wild Horse Range
Fertility Control Preliminary Environmental Assessment Tiered to the Pryor Mountain Wild
Horse Range Environmental Assessment and Herd Management Area Plan May 2009 EA DOI-BLM-MT-0010-2011-0004-EA. My background is in equine reproductive immunology and wildlife conservation. I applaud the Billings Field Office of the Bureau of Land Management (BLM) for a thoughtful approach to this issue. Cover letter 4700 (010.JB) dated November 2010 and signed by James M. Sparks, Field Manager states that the BLM would consider comments and revision to the EA or unsigned FONSI as appropriate. I urge a “no action alternative” as outlined on page 7 and 8 of the EA. This request is based on two pieces of new scientific evidence about effects of current immuno-contraception use.

Porcine Zona Pellucida (PZP) Contraception

The proposed action as stated on page 7 of this EA would exempt “mares ages 5-10 unless they have produced foals, or are part of a large bloodline.” This is reminiscent of the approach taken with the Assateague Island wild horse population. It is a compromise approach to this issue, in comparison to placing all mares on PZP. However a recent study shows that mitochondrial DNA diversity is low in the Assateague Island horse herd (Eggert et al. 2010). Since mitochondrial DNA is inherited from the mother (mare), this is evidence that female inherited genetics on Assateague Island wild horses is under represented. It is imperative that this be assessed before rolling out a similar management plan for the Pryor Mountain wild horses.

There is a recent Princeton University study on PZP effects. Consecutive PZP applications, analogous to the proposed action plan in this EA, showed that mares gave birth later in the season, and were cycling into the fall months (Nunez et al. 2010). In a state like Montana where freezing temperatures are found in the fall, this can have serious and long term effects on foal survivorship.

I must include a statement on long term consecutive use of PZP. Any form of PZP contraception is not completely reversible in mares depending on the length of use of PZP. Contraception can only be reversed when the antibody titer decreases to 50-60% of the positive reference sera (Liu et al. 2005). Mares treated for 7 consecutive years do not return to viable fertility (Kirkpatrick and Turner 2002; Kirkpatrick et al. 2009). The issue of reversible contraception is very important to be able to maintain wild equines in the United States. Long term treatment with PZP has inherent negative potential for this herd.

I am requesting a new look at the proposed fertility control action for the Pryor Mountain wild horses.


Christine DeCarlo, Ph.D.

Lori S. Eggert, David M. Powell, et al. (2010). “Pedigrees and the Study of the Wild Horse
Population of Assateague Island National Seashore.” Journal of Wildlife Management
74(5): 963-973.

J. F. Kirkpatrick, A. Rowan, et al. (2009). “The practical side of immunocontraception: zona
proteins and wildlife.” J Reprod Immunol 83(1-2): 151-7.

J. F. Kirkpatrick and A. Turner (2002). “Reversibility of action and safety during pregnancy of immunization against porcine zona pellucida in wild mares (Equus caballus).” Reprod
Suppl 60: 197-202.

I. K. Liu, J. W. Turner, Jr., et al. (2005). “Persistence of anti-zonae pellucidae antibodies
following a single inoculation of porcine zonae pellucidae in the domestic equine.”
Reproduction 129(2): 181-90.

Cassandra M. V. Nunez, James S. Adelman, et al. (2010). “Immunoctraception in Wild Horses (Equus caballus) Extends Reproductive Cycling Beyond the Normal Breeding Season.” PLos ONE 5(10): 1-10.

(Posted for educational purposes)


Science proves PZP is sterilizing wild horses

The truth

The Effects of Porcine Zona Pellucida Immunocontraception on Health and Behavior of Feral Horses (Equus caballus)

Authors: Knight, Colleen M.
Advisors: Rubenstein, Daniel I.
Department: Ecology and Evolutionary Biology

The horse population on Shackleford Banks, a barrier island off the coast of North Carolina, has been controlled using a program of porcine zona pellucida immunocontraception since 2000. Prior studies found no negative physiological effects of the immunization, but suggested some adverse effects on behavior such as increased harem switching and extended reproductive season. Although no mares were immunized in the year of study (2013), we examined the effects of past contraception and foaling on health and behavior of the mares in an attempt to better understand its impacts on both the individual and the population. Current lactation was found to be the best predictor of health and behavior: lactating mares were in worse physical condition, spent more time grazing, and switched harems fewer times. Mares that had never foaled also were in better physical condition than mares that had foaled in the past, but did not differ in behavioral measures. There were indications that the PZP treatment has had effects other than preventing pregnancy: an increased number of years since immunization was correlated with better body condition and fewer harem switches, independent of lactation. Contraception treatment intensity or timing did not have any significant adverse effects on health and behavior on its own. However, three or more consecutive years of treatment or administration of the first dose before sexual maturity may have triggered infertility in some mares. Inducing sterility, while relieving the mares from the energetic costs of lactation and reducing the stress from harem switching, may have unintended consequences on population dynamics by increasing longevity and eliminating the mares’ ability to contribute genetically.

Read more here: http://dataspace.princeton.edu/jspui/handle/88435/dsp01vt150j42p

Sign and share the urgent petition: Grant a 10-year moratorium on wild horse roundups for recovery and studies

PZP is an EPA approved restricted use pesticide and Protect Mustangs is against using it on wild mares especially when there is an underpopulation problem on public land despite government spin. The truth is most wild herds are being threatened with low numbers and a lack of genetic variability.

A dark day for native wild horses ~ National Academy of Science Report published

Photo courtesy BLM

Photo courtesy BLM

The NAS report has been released and is found here.


Statement from Anne Novak, Executive Director of Protect Mustangs

We are grateful that the National Academy of Science (NAS) recommends stopping cruel roundups  but we challenge their decision to control alleged overpopulation like a domestic herd with humans deciding who survives and breeds.

NAS deploys the BLM overpopulation myth to push EPA restricted use PESTICIDES (Immunoconraceptive PZP & GonaCon®) as well as sterilization on Native #WildHorses.

This is part of the plan named after Ken Salazar, the previous Secretary of Interior, whose mission was to wipe wild horses off public land, stockpile them at taxpayer expense and send many into the alleged slaughter pipeline.

The Salazar Plan began in 2009 -10, despite public outrage. Its focus was to remove wild horses and burros to facilitate the energy and water grab on public land.

The renewables market abroad is hot. Fracking and exporting natural gas through pipelines across the West is causing environmental damage. Wild horses would require mitigation so they lobbied for the BLM to get rid of them.

The Salazar Plan feigns an overpopulation crisis to remove most native wild horses from their legally designated ranges and stockpile them in government holding. They are torn from their homes, families and at risk of being sold to probable slaughter.

Overpopulation is a MYTH used to ruin native wild horses. There are maybe 18,000 wild horses left on more than 31.6 million acres of public land designated for their use. They are reproducing at a higher rate because nature knows they face extinction from the gluttony of roundups since 2009. Immunocontraceptives are risky. Sterilizing them is wrong. Put the 50,000 in holding back on the range so they can fill their niche in the ecosystem.

We are witnessing the final attack on the indigenous horse and it must be halted.

Man-made fertility control will domesticate wild horses and wipe them out. Survival of the fittest is Mother Nature’s way to select who breeds to protect the herd.

Domestic horses are manipulated by man. Their weaknesses are evident as a result.

We ask the NAS, the BLM and certain members of the advocate community, “Do you really think man can choose who breeds better than nature? Do you realize that by supporting chemical fertility control many will be sterilized and loose their place in the herd?”  What happens when they all die off?  Will you then realize they were never overpopulated?”

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Statement from Jesica Johnston, MA Environmental Planning

The National Academy of Science’s findings clearly state that the Bureau of Land Management (BLM) has failed to provide accurate estimates of the nation’s population of wild horses and burros. Therefore, the NAS cannot conclude that a state of over-population exists and or provide a recommendation for artificial management considerations such as “rigorous fertility controls” to control populations for which the complex population dynamics are currently unknown. However, the NAS is recommending science-based methods to improve current management practices, population estimates, and the overall health of the ecosystem which could provide key information toward sustainable and effective management that could prevent the removal of wild horses and burros from our public lands.

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Dead wild horse (Photo © Craig Downer)

Dead wild horse (Photo © Craig Downer)

Statement from Craig C. Downer, M.S., Wildlife Biologist, Wild Horse Expert, Author and Founder of the Andean Tapir Fund

BLM plans to use “aggressive birth control” to prevent the expansion of the wild horse/burro populations that remain. Chief among the drugs to be used is PZP (porcine zona pellucida). This injected drug covers the eggs, or ova, of mares, preventing sperm from fertilizing them. It is experimental, however, and has some questionable effects upon the horses themselves, both individually and collectively. For example, its effect leads to mares’ repeatedly recycling into estrous, thus stimulating stallions to repeatedly mount the treated mares — all to no avail. This frustrating situation causes much stress among individuals of both sexes and a general disruption of the social order, both within bands and, as a consequence, within the herds themselves.

Other unintended consequences of PZP are out-of-season births occurring after PZP’s effect has worn off after a year or two.  These births have been observed during the colder late autumn and winter seasons (e.g. Pryor Mountains her by G. Kathrens) and their un-timeliness causes suffering and death among both foals and their mothers.

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The underside of a skull, showing palate and teeth, of Equus scotti is seen in this photo provided by the San Bernardino County Museum. The remains of the Ice Age horse were found for the first time at Tule Springs in Nevada.

The underside of a skull, showing palate and teeth, of Equus scotti is seen in this photo provided by the San Bernardino County Museum. The remains of the Ice Age horse were found for the first time at Tule Springs in Nevada.

Statement from Debbie Coffey, Director of Wild Horse Affairs, Wild Horse Freedom Federation

PZP and other fertility control should NOT be used on non-viable herds.   Most of the remaining herds of wild horses are non-viable.  The NAS and any advocacy groups that are pushing PZP and other fertility control have not carefully studied all of the caveats in Dr. Gus Cothran’s genetic analysis reports along with the remaining population of each herd of wild horses.
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By U.S. Government [Public domain], via Wikimedia Commons

By U.S. Government [Public domain], via Wikimedia Commons

Statement from Jennie Barron, Director of Wild Horse Hub Central

1. Wild horse mares that are darted with PZP can become permanently sterile, making the viability of the herd impossible as the older mares die, there are no mares to have foals.

2.  If the Lead Mares are darted with PZP, they can become sterile, making the family herd disorganized; the stallion does not understand why she won’t foal; and she may leave the family herd she knows because of the disorientated. This has happened with older mares as they are not able to foal and they are the lead mares, leaving no mare to teach them where to graze, find minerals, water, or when to do certain things that wild horse herd families do.

3.  The mares who are pregnant after they have been darted with PZP can and do foal out of season. This means that they can not keep enough milk for the foal; and the winter weather is too harsh for the foal to survive. Prognosis: death.

4.  Considering the consequences stated above, this is too risky a business to lay at the feet of an already depleted wild horse herd. It must be taken into consideration that PZP is just as dangerous as a mountain lion, it is permanent, and it is deadly.

# # #

(Photo © Anne Novak, all rights reserved.)

(Photo © Anne Novak, all rights reserved.)

Statement from Carl Mrozek, Filmmaker of Saving Ass in America

To its credit the extensive review of the BLM’s failed Wild Horse & Burro Program criticized the agency for relying primarily on aggressive culling of wild herds primarily via helicopter roundups which “perpetuate the overpopulation problem by maintaining the number of animals at levels below the carrying capacity of the land, protecting the rangeland and the horse population in the short term but resulting in continually high population growth and exacerbating the long-term problem” the National Academy of Sciences” declared in a preliminary press release.  What they’re referring to is the principle of compensatory reproduction by heavily-stressed wildlife populations needing to rebound from population declines due to many factors.

Unfortunately, they quickly recommend a different intervention as a better solution without considering the ‘ do nothing”  or ‘placebo’ option which is an integral component of every credible field trial for pharmaceutical and other ‘treatment plans. Had they searched for examples of herds which have undergone minimal or no culling in the past decade or so, they would have found multiple examples of herds which appear to have achieved homeostasis (equilibrium) or something approaching it, naturally, i.e. without BLM-sponsored roundups or fertility treatments.

At least two mustang herds I’ve observed and filmed in Nevada and Arizona over the past 5-7 years meet those criteria, and some burro herds as well. The important point to remember, is that all of those herds cost the taxpayer virtually zilch to maintain in the wild. This contrasts with the cash-intensive hands-on management strategy revolving around helicopter roundups, warehousing of captured animals for life in long term and short term corrals and feedlots, as well as the fertility treatments, -the least costly and disruptive of these predominant management methodologies.

The bottom line is that sometimes we can do more, and do better, by doing less, or by letting Mother Nature do what she does best: sow and weed.

Hopefully, this option is explored somewhere in the freshly released report, and will be actively considered by the new hierarchy at BLM and the Dept. of Interior, and with much more intensive collaboration with wild equine afiscionados  committed to the survival of these herds in the wild as intended by the Free Ranging Wild Horse & Burro Act of 1971.

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PM Hazard Foter Public domain Marked Sterilize


Statement from  Jaime Jackson, Executive Director and the founder of the Association for the Advancement of Natural Horse Care Practices

“Whether wild horses are sterilized or chemically “contraceptized”, at stake are the forces of natural selection being usurped by what will be tantamount to a program of “domestication eugenics” — humans determining who gets to breed and who doesn’t in wild horse country. If that door is opened, we will have turned drug companies and profiteers loose on our wild horses. We now know with certainty that such veterinary/medical interventions cause laminitis, colic, and other types of metabolic breakdown and disease. More drugs will then be needed. Thus, more profits will be pocketed. A brutal cycle is unleashed that causes harm to any horse, wild or domesticated.

“…What we are talking about here is the de facto domestication and subsequent contamination and destruction of America’s wild, free-roaming horses. It is bad enough what we’re also doing to another 51,000 who are captured, and stand idly by at tax payers expense in government holding corrals and private “preserves”? Support the misguided’s push to turn wild horses into pathological parodies of their personal horses? No thanks!

“The AANHCP offers another vision for genuine wild horse preservation that clear thinking people should be able to understand. This vision will do all things that eugenics can never do. And humanely so without compromising natural selection or burdening the tax payer. So, if you really want to help our wild horses, say no to the Obama Administration and the National Academy of Science’s “zero them out” for the corporate land grab, say no to [any] eugenics visions, and no to the drug companies and PZP (and other) pharmaceutical patent holders hungering for the ovaries, testes, and DNA of our America’s wild, free-roaming horses in the name of profiteering at the animal’s genetic expense.

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Sam (#3275) is from California's High Rock area (Photo by BLM)

Sam (#3275) is from California’s High Rock area (Photo by BLM)

Statement from Valerie Price, Biological Researcher

PZP is a pathogen derived immunocontraceptive vaccine, it SHOULD be intended for use ONLY in captive animals. PZP stands for Porcine Zona Pellucida. This, and other immunocontraceptive vaccines are derived from pathogenic bacterias. PZP contains Mycobacterium tuberculosis, the organism that causes tuberculosis in humans and many species of livestock, including cattle. The bacterial component of the vaccine is supposed to be a killed form, but due to the potential for bad lots causing live tuberculosis to be transmitted to humans and animals, and due to concern over the possibility of contaminating the food web, PZP would have been unlikely to recieve approval by the FDA. Instead, the EPA approved PZP as a pesticide, leaving public health professionals in ignorance of the biological nature of this vaccine. It remains unclear whether the restrictions for use allow for any PZP treated animals to be released into the wild. While such a release could pose an ongoing threat to public health for both humans and animals, the effectiveness of PZP as an immunocontraceptive vaccine is negated by only 10% immigration or emmigration into treated herds, according to a study conducted by Texas Parks and Wildlife with captive, white tail deer.

A recent clinical study in cats treated with PZP found a high percentage of injection site abscesses. Rumours of abscesses occurring in horses treated with PZP by the BLM has raised the spectre of possible bad lots of vaccine already having been used. Human exposure to tuberculosis could possibly be a concern and it is recommended that all BLM agents and equine advocates who have come in contact with the vaccine, or with treated animals, be tested for tuberculosis, to ensure the bio-security of the public.

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PM Gov Land Map.jpg.jpe

Statement from Lisa LeBlanc, Independent Researcher & Equine Advocate:
We can not depend on ‘estimates’ of on-the-range populations or the accuracy of ‘reports’ of nearly 50,000 in captivity; neither history nor biology support the Bureau’s claims. There is a supposition that wild equine advocates have no notion of the enormity of wild or captive wild populations due to a ‘sympathetic’ response, but we can only base our data on the information we’re given, and the knowledge we already possess. For example:

Absence of any data indicating mortality, either on-the-range or in holding.

Denial of ‘reciprocal’ breeding, that is, the animal’s biological imperative to replace what’s been taken.

Absence of knowledge of specific herds and their behaviors, key factors in determining accuracy of foaling rates, which often fall far below the National average of 20%.

On-the-range herd management must be as accurate as possible, visually documented for Public use and managed through science and study. How can effective management occur if the basis of all aspects is ‘estimate’?

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Check back for more statements from wild horse and burro influencers. We are updating this page.