Wild Horse Education

Facts on PZP and why

Introduction by Laura Leigh. I tell our volunteers to analyze issues, law and tools available. I tell them to look for facts, not farts (I know, brash and inappropriate). A lot of the gas passed has a foul smell like a lot of our riparian areas on public land and is filled with the fictions to justify exploitation. But there are also unicorn farts, the vapid vapors of those disconnected from reality and looking for a utopia of rainbows and jellybeans.

Our volunteers are concerned, justifiably, with the way all of this actualizes on the ground and impacts our wild ones. The following is a piece compiled by one of our volunteers and our board has chosen to share it.

Beth Quigley Lauxen, WHE Volunteer; Laura Leigh and Wild Horse Education have fought hard for our wild horses and burros, and have won amazing court battles. The legal strategy was game changing. We now have the beginning of a humane handling policy that was the result of multiple legal wins against inappropriate conduct at roundups (the only org to ever litigate these issues). A landmark ruling was won for First Amendment Rights of the public to have access to document handling during roundups and in holding. She fought through life-threatening illness, yet never stopped her battles on the ground. WHE began looking for a way to actualize the humane mission on the range, where it matters most. Instead of celebrating the enormous achievements, Laura and WHE have faced relentless attacks, from certain factions/orgs whose agendas seem to be to hurt WHE funding, or against her personal safety. These types of serious threats emanate from users or supporters of competing private interests for the use of public lands. I look for ways to minimize such conflicts that are at minimum distractions from making the progress she saw so critical to progress to save our wild ones.

I have reworked several articles published by WHE in the past into one. The myths surrounding the use of PZP, as well as the myths around why the vast majority of advocates favor it, are many. I am making this attempt to assist with public understanding of the position of Wild Horse Education. Yes it is a long article. The need to keep things to a simple explanation create far more problems than they solve. Take the time, it is the most important thing to give something you care about.

At present Wild Horse Education is active in the pursuit of the use of birth control in the form of PZP and simultaneous data collection on the range, to assess scientifically, existing management plans, and gathering the data needed to change those plans through appropriate processes, in order to preserve and protect wild horses free on the range. The use of a form of PZP (native) has multiple practical purposes for implementation. It slows population growth and allows data collection from herd structure, genetic maps, migratory patterns (that includes boundary issues), and forage utilization. It adds the ability to create and track these aspects of the herd in a “trend map” which can these be used to address the planning process from a scientific basis. Isn’t that what is lacking in the program? Won’t that allow things like genetic bankruptcy to be addressed and any flaws like numbers of horses on the range to be modified? In June of 2013 the National Academy of Sciences (NAS) after conducting a million dollar report, released a report on the BLM Wild Horse and Burro Program. https://wildhorseeducation.org/2013/06/05/nas-report-a-first-look/ This 400 page report essentially delivers a FAILING GRADE to BLM’s wild horse and burro management program, based on a lack of scientific justification for any decision making. One of the NAS admonishments was that BLM failed to use PZP appropriately (often applied at the wrong times of year) and in less than 3% of the wild horse population.

Let’s look at some FACTS on PZP, versus the MYTHS that are perpetuated by others who do not know the facts, or worse, by organizations claiming to be advocates for the mustangs, yet whose agendas are indeed to create and perpetuate PZP Myths, in order to use emotional manipulation of the uneducated public, while offering up no alternatives to use in the fight to actually keep wild horses and burros managed on the range.

What is PZP? (taken from the PNC project for wildlife contraception)
A non-cellular membrane known as the zona pellucida (ZP) surrounds all mammalian eggs. The ZP consists of several glycoproteins (proteins with some carbohydrate attached), one of which, ZP3, is thought to be the sperm receptor (the molecule which permits attachment of the sperm to the egg during the process of fertilization). The PZP vaccine is derived from pig eggs. When this vaccine is injected into the muscle of the target female animal, it stimulates her immune system to produce antibodies against the vaccine. These antibodies also attach to the sperm receptors on the ZP of her own eggs and distort their shape, thereby blocking fertilization (see Paterson and Aitkin 1990).

Thus far PZP has been a promising form of contraception in wildlife because

1. it has prevented pregnancy an average of 90% of the time in treated animals
2. it can be delivered remotely by small darts
3. the contraceptive effects are reversible
4. it is effective across many species
5. there are no debilitating health side-effects even after long-term use
6. it has almost no effects on social behaviors
7. the vaccine cannot pass through the food chain
8. it is safe to give to pregnant animals (see Kirkpatrick et al. 1996b).

So why are these points being either misrepresented or ignored?
It may be the use of terminology used in research and implementation documents. We will try to explain some of the terms and why.

MYTH: “Pesticide.” PZP is not DDT. PZP is a protein that breaks down. That is one of the reasons it is only effective for one year (one reproductive cycle for wild horses, they do not breed like rabbits). The classification is because of the purpose of use and was “put on the books” first in the US for dealing with deer populations for “pest control.” We might not like the term, but the classification is not because this is like DDT or RAID.

MYTH: “Soil and water contamination.” PZP is a protein that breaks down. It has been used for decades in deer, wild horses, elephants etc. We do not have birds and fish and squirrels dying in Assateague from PZP use since 1988 or lions or coyotes from the use on deer and elephants. Scientifically this is purely not the truth.

MYTH: “If you want PZP you believe all horses are feral.” This is another term that can make a wild horse advocate see red. But the use of PZP does not change the legal definition of a horse. A horse (or burro) is legally designated by where it stands on the land. A horse on state land or Fish and Wildlife is legally designated as “feral.” A horse on BLM land has the legal definition of “wild.” Treating a mare at McCullogh Peaks does not change her status to feral under law. So if you read the word in research documents please understand why before reacting to it.

MYTH: “Behavior Changes.” All kinds of behaviors are being attributed to PZP use from gang rape to foal murder. At Assateague we do not see tourists running screaming after watching the horses, we see them taking their children and the community getting a great reputation. In wild, untreated populations, stallions have been documented killing foals (although rare) and mares are mounted by more than one stallion (again rare, but documented). PZP also wears off and any stressor associated with any lack of fertile mares could be relieved in contrast to surgical techniques like those used at Sheldon National Wildlife Refuge (we documented how vasectomies keep males thinking they are fertile and a lack of fertile females due to hysterectomies create an intensity in behavior we, personally, have witnessed nowhere else).

MYTH: “Harder to Catch and will make ‘gathers’ more difficult.” This assertion has no basis in any factual information as no widespread use of PZP has been implemented on any significant portion of the wild horse population on BLM or FS land. And indeed if PZP native is successful, what will be the result? Helicopter removals would be increasingly diminished in any area treated, because remote daring is the primary tool for application.

Some more terms thrown:

“Overpopulation.” This seems to be the most recent “buzz word.” There are accusations that if you support the use of PZP, you agree to “overpopulation.” This is a spin worthy of Maytag. The term overpopulation (in discussions on BLM land) arrives from another term “Appropriate Management Level” or AML. This is the number of animals BLM says the land can sustain. The levels are set in a land use planning process (for decades not engaged by the advocacy community). The term creates a legal definition, not a justified one. If we go back to what WHE has been saying (as an example in court documents on Owyhee) is that AML is not based on any scientific equation. The NAS concurred in their report that also admonished BLM for not using birth control.


The current accuracy of asserted AML is absolutely suspect, but real and legal nonetheless. In order to change AML data must be present. In order to adjust boundary lines data must be present. A significant lack of data has left wild horses and burros vulnerable to competing interests, fighting for control of public land. Those battles have intensified due to drought and pending Sage Grouse plans which are broad and sweeping. The NAS report is currently under review by BLM to determine how they will translate that report into recommendations. NAS’ core recommendations were to utilize birth control (PZP) and data collection to slow population growth while using scientific date to accurately determine AML. More accurate AML recommendations could then be made by BLM as multiple land use plans define Appropriate Management Level (AML) under the law.

“What is so frustrating is that these ‘mathematical notions’, originally used to arrive at AML, only work on one side of an equation,” said Leigh. “If BLMs monitoring is flawed, then it was also flawed in determining AML, making AML an inaccurate barometer of range or herd health. If the data is flawed then it is flawed. BLM can’t claim accuracy in one portion of management to further their agendas, when they base their agenda on the claim of inaccuracy. I agree the data is, and has been flawed. The notion that AML is a ‘truth’ is indeed pure fiction. In many areas the number of wild horses considered ‘appropriate’ is significantly below any real level of genetic sustainability and simply represents the leftovers in the equation.”

BLM uses the term “overpopulated.” That term means that wild horse or burro populations exceed AML (Appropriate Management Level). That is all it means. It does not validate that there are too many horses. It simply means that there are more wild horses on a range than a land use plan prescribed. A land use plan that we know was not based on data. BUT it is an enforceable number because it is the operational standard. WE use the term “overcrowded.” Wild horses and burro ranges are utilized by multiple entities that create artificial and impeded use of wild horse Herd Management Areas (HMA). There are too many users crowding the horses. So how do you deal with both terms? The distinction in meaning becomes rather irrelevant to the steps required to rectify the situation that is at the core of the “crisis” of 50,000 wild horses sitting in holding facilities and our western ranges being used as a “disposable” resource.

Either way you look at it “overpopulation” or “overcrowded” the steps forward to create actual preservation of resource and wild horses and burros are identical. KNOWING the range and the herds that occupy them, based on scientific evaluation of actual data, will erase the game of “too many horses” simply because someone says so. It will erase the accusation of “you don’t know anything; my family has lived here for a hundred years.” It will create management based on an actual truth.

Using PZP for birth control (as recommended by the NAS and advocated for years by those trying to protect wild horses) creates the need to gather utilization data. How do the wild horses and burros use the range? What might be critical habitat to their survival? What is the herd structure? What is the genetic bank involved and how fast is it depleted? Is distribution an issue due to improper boundary lines and limited water sources?

All of those questions can be answered in site specific fashion. In each area an equation can then be developed to determine exactly what is “AML” and adjust those that are not based on anything but “what is left over” after other uses (like massive livestock use or water use). The resources required to protect those populations (as the law intends) will be identified so that their preservation can be fought for.
We ask that YOU keep in mind the “big picture” of 50,000 wild horses in holding facilities, proposals to surgically sterilize wild horses, legal actions against horses by the livestock industry, changing public land policy, with a push from the right to privatize public lands, sage grouse, and drought and water issues. Then we ask that you put PZP in perspective as one of the tools that can be utilized to satisfy legal requirements and gather real data that can then be used to create sound management plans.

If you look at the work of WHE… all of our work… are we spending the vast majority of our time on PZP? Or are we working very hard on multiple levels to actively engage to protect wild horses and burros from abuse, slaughter and extinction? PZP is one tool that we are simply not using as we should.


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Categories: Wild Horse Education