Wild Burros

Drugging wild horses is not sound wildlife policy

The drug PZP can be administered by darts (pictured) or through a hand-delivered jab stick. (Photo by Phil Taylor, E & E Reporter)

Source: Elkodaily.com

Commentary by Michael Ray Harris  (Michael Ray Harris is the director of the Wildlife Law Program for the animal advocacy organization Friends of Animals. He is located in Colorado.)

There is a lot of talk going on regarding whether the fertility drug porcine zona pellucida (PZP) is a magic bullet to control what some believe is an overpopulation of wild horses in the West. Organizations like the Humane Society of the United States and the American Wild Horse Preservation Campaign claim that PZP is a safe and effective way to “responsibly manage” the horses. As such there is a huge push to get state and federal wildlife officials to dart as many wild mares as possible with the drug this year.

The assertion that the use of PZP does not “harm” the horses is, however, scientifically questionable. While scientists associated with the Humane Society have researched the efficacy of the drug on controlling fertility, these pro-PZP researchers have ignored research on the negative effects the drug can cause the horse.

Independent research shows that PZP — which is derived from pig ovaries and is registered as a pesticide by the Environmental Protection Agency — can have lasting adverse effects on wild horses. According to Dr. Cassandra Nuñez, PZP is associated with ovulation failure and can alter the birthing cycle of wild horses, resulting in birth out of season where the foal can die for lack of available food.

Dr. Nuñez also found that PZP has significant consequences on social behavior of wild horses. Normally bands of wild horses are very stable, and mares will stay with males for much, if not all, of their lives. However, when mares have been treated with PZP and cannot get pregnant, they may leave their bands. This creates instability in the bands and effects the health of the group members. The instability caused by PZP causes increased mortality, and can cause the parasite load of animals in the group to go up because of increased stress.

Thus, the fundamental problem with PZP, from an animal activist’s perspective, is that the drug can deprive the horses of what the renowned American philosopher Martha C. Nussbaum has called “species-specific, basic capabilities:” life, bodily health, bodily integrity, play, sense/imagination/thought, emotion, affiliation, and control over one’s environment.

What is ignored by the pro-PZP community is that wild horses darted with PZP to inhibit their ability to naturally reproduce aren’t really, well, “wild” anymore. “Wild,” means “living in a state of nature” as opposed to being “tamed or domesticated” to be more useful to humans. Accordingly, opposition to PZP is based on an ethical belief that wild animals should be free of human manipulation.

Read the rest if this commentary HERE.

Read the EPA Pesticide Fact Sheet HERE.

28 replies »

  1. Hi Priscilla,

    With control of the lands going back to the States we should also have control of our wild animals too. He has taken the power away from the BLM and others. I was told that he also told them no more weapons. This should get very interesting soon. But I don’t believe that it is totally over yet but we are off to a great start.


    Sent from Outlook


    Liked by 1 person

  2. PZP is an EPA registered PESTicide. The term “-cide” comes from the Latin word “to kill.”
    a substance used for destroying insects or other organisms


  3. OMG – and these side effects are worse than being rounded up and held in pens for the rest of their lives or slaughtered??? I am all for PZP control…. please look at the alternatives!! “not managed & free” is not an option here…..


  4. Not sure if this was posted intentionally on this blog – but putting control of the public land in the States hands would seem to be the end of our wild horses AND the beginning of the complete destruction of the range. I’m not going to comment any further on the above email – would most certainly go down the wrong path. I agree with the article – there is NO over-population of wild horses or burros – I understand some groups are grabbing at whatever seems to stop roundups.

    Liked by 1 person

  5. Do not allow the BLM and USFS and Farm Bureau and the extractive and mining giants and the domestic livestock grazing associations to pull the wool over your eyes. There are no excess wild horses and burros on their legally designated land. Per the United States 1971 Congressional Wild Horse and Burro Act, the land is to be devoted principally although not exclusively to the wild horses and wild burros’ welfare in keeping with the multiple-use management concept of public lands. Many tend to view members of the animal kingdom to be valueless unless they can be reduced to mere “commodities;” if the animal cannot be sold or traded, then it is no more than a mere pest to be eradicated to make way for human development.

    There is no reason for these wild horse and burro removals and destruction procedures … because there is no “over-population” of wild horses and burros on their legally designated land. In 1971, when Congress passed the Wild Free-Roaming Horses and Burros Act, these animals were found roaming across 53,800,000 million acres. That amount of acreage could support more than about 250,000 wild horses and burros but even after 22,200,000 acres were stolen from the American people by government agencies the remaining 31,600,000 acres could easily support more than 100,000 wild horses and burros today.

    The recent National Academy of Sciences study found NO evidence of overpopulation of Wild Horses and Wild Burros. Obviously, the government’s actions toward the wild horses and burros needs to be closely and independently investigated and the animals left (and returned) on their legally designated land. There is no reason for these wild horse and burro removals and destruction procedures … because there are no excess wild horses and burros on their congressionally designated legal land.

    I know that different Wild Horse and Burro legal land varies but why aren’t the organizations that support PZP doing independent fly-overs and scientific studies on the TRUE populations? Why? Because there is no evidence of any excess wild horses and burros on their legal land. When there is, then we can talk about contraception but until then …


  6. The author, MaryBeth Devlin, was having internet issues and asked me to post this:

    1. PZP — The Pesticide: PZP is an EPA-registered pesticide manufactured from the ovaries of slaughtered pigs. Some persons argue that, because PZP does not kill the mare, it is not really a “pesticide.” Actually, PZP does kill. Stillbirths are associated with the pesticide’s use, meaning that some of its supposed contraceptive effects are actually feticidal. In addition, over the long term, PZP weakens a herd immunologically, putting it at risk for eventual or even sudden extinction.

    2. PZP — The Disproved Hypothesis: PZP’s manufacturer promoted the product as generating antibodies that “block sperm attachment.” But that marketing-hype was merely an untested hypothesis postulated three decades ago. Independent researchers found that PZP has a different effect, and many adverse effects.

    3. PZP — The Actual Mode-of-Action: Behaving like a perverted vaccine, PZP tricks the mare’s immune system into making antibodies that cause ovarian dystrophy, autoimmune oophoritis, ovarian cysts, and premature ovarian failure. PZP quickly sterilizes mares that have a strong immune system but has no effect on those suffering from weak immunity. Thus, PZP both works and doesn’t work but, in the long run, selects for poor immune function. Weak immunity = weak resistance to infection, which could quickly wipe out a herd. PZP also affects the foals. If a mare is pregnant or nursing when darted, PZP antibodies are transferred to her offspring via the placenta and her milk. So, inadvertently, unborn and newborn foals receive a dose or two of the pesticide when their dams are injected.

    4. PZP — The Danger to Darters: PZP is a powerful endocrine-disruptor. It causes a sharp drop in estrogen levels. Unfortunately, because the manufacturer misrepresented PZP as “so safe it is boring,” volunteer-darters have become lax in following safety-precautions. Accidental self-injection could result in severe adverse effects because the dose-in-question is sized for a horse.

    5. PZP — The Year-Round Birthing-Season: A longitudinal study (Ransom et al. 2013) of three herds currently under treatment with PZP found that the the birthing-season lasts virtually year-round (341 days). Out-of-season births put the life of mares and their foals in jeopardy. Nature designed foals to be born in Spring, not year-round, and certainly not in Winter.

    6. PZP — Prolonged Delay in Recovery of Fertility: Ransom et al. also found that, after suspension of PZP, it takes more than a year per each year-of-treatment before mares recover their fertility. PZP’s manufacturer conceded that it could take up to 8 years to recover fertility after just 3 consecutive years of PZP treatment.

    7. PZP — Scientists Say Proceed with Caution: Ransom et al. warned: “The transient nature of … PZP can manifest into extraordinary persistence of infertility with repeated vaccinations, and ultimately can alter birth phenology in horses. This persistence … suggests caution for use in small refugia ….”

    8. PZP — Contraindicated for Small, Isolated Herds: Several years ago, BLM convened a meeting of scientists on the topic of minimum herd-size for genetic fitness. Conclusion: “Smaller, isolated populations (<200 total census size) are particularly vulnerable …." Per the guidelines of BLM's own geneticist, 83% of the wild-horse herds — and 90% of the wild-burro herds — suffer from arbitrary management levels (AMLs) set below minimum-viable population (MVP).

    9. Slow Herd-Growth: Per independent research, wild-horse herds increase at a rate of only 5% a year; and wild-burro herds, just 2%. Such slow growth does not warrant pesticide treatments administered en masse. BLM knows this but continues to publish fraudulent herd-growth data that are orders-of-magnitude higher than the reproductively possible. Thus, PZP-promoters are, misguidedly, rewarding BLM's criminality and further penalizing the underpopulated and slow-growing herds of wild horses and burros.

    10. Natural Solution: The right way to right-size the wild-horse population is Nature's way — predators. Mountain lions, bears, wolves, and coyotes help the herds by favoring survival-of-the-fittest and the best genetic adaptations. Predators must be protected and allowed to fulfill their role. Cost: $0.


  7. As so often happens when an issue is hotly debated, some essential facts are swept away by emotion. Dr. Kirkpatrick’s original version of the drug, PZP 1 which lasts one year, has an over two-decade track record of successful and healthy herd management in controlled situations such as the Chincoteague Ponies and North Carolina Outer Banks herds. It is also being used successfully by darting with the 130-member herd of wild horses on a private nonprofit reserve in Idaho. BLM demanded and got a stronger version, PZP 22 which lasts three years, and to which he was philosophically opposed. Their failures with this have been as much from improper storage and administration as to the questionable side effects of the drug itself. Whether PZP was originally a pesticide is irrelevant. Many drugs developed for one use find better applications elsewhere. An example horse people will understand is phenylbutazone, which was originally developed as an arthritis medication for humans. Today it is our primary argument for ending equine slaughter. Contraceptive drugs are certainly not the end all solution for wild horse management, but use of the proven version properly can be one more tool in the bag. We are attempting to halt the tribal roundups for slaughter here in Washington State and proper use of PZP 1 for herd management on the reservations is on of our strongest arguments that there are viable alternatives. Working with Dr. Kirkpatrick we actually tried to convince the Yakama Nation to try this several years before the roundups even started, sadly to no avail. In the meantime the debate about this itself has probably proved more damaging the wild horse advocacy than the drug itself ever will, because it has become such a divisive issue among so many people who all have the same ultimate goal, preservation of our wild ones in their natural habitat.

    Liked by 2 people

      • In addition, every time the issue of fertility control is brought up, all wild horse and burro advocates should be hammering the BLM on their bogus population estimates, and calling them out for claiming there is an “overpopulation” of wild horses and burros.

        Liked by 2 people

  8. HOW does this effect the Mares?
    HOW does it effect the band behavior?
    We must not forget that there has also been sex-ration skewing implemented on these Wild Herds, which has negatively effected Wild Horse band behavior.
    The next step, as has been repeatedly done, is to zero out a Herd Management Area because “there are too few Wild Horses or Burros remaining”
    22 Million Acres have completely disappeared from Wild Horse & Burro Herd Areas.
    The Wild Herds have been skewed and the American Tax-paying Public has been screwed.

    Liked by 1 person

  9. Another Wild Horse program we need to make certain doesn’t attempt to bash the Wild Horses for being supposedly overpopulated.


  10. Here are just a few of many wild horse fallacies that BLM publicly publishes and uses to fool the public and Congress (for funding) that there is an “over-population” of wild horses.

    FOX HOG HMA (NW Nevada) supposedly had a 153% increase in ONE year. That would be 144 horses having 220 surviving foals in one year.
    …and in that same year the nearby
    HIGH ROCK HMA supposedly had a 187% increase in ONE year. That would be 124 horses having 232 surviving foals.


  11. Harmonyhorseallen is spot on. Once again, fake facts from Friends of Animals are being used to divide advocates and divert attention from the real issues. FOA is suing local advocate partnerships to stop PZP; their real aim appears to be to bolster the slaughter industry and keep wild horses off the rangelands that are theirs. PZP is like the pill for women: it leaves natural behavior intact, with the only exception being that mares have slightly more choice in partners. We can all howl to the moon wishing for everything to be perfectly natural and pre-human, whatever that would mean. The fact is, PZP is one tool that presents one alternative to the BLM’s roundup and removal policy. Other alternatives would include creating more WH ranges like the Pryors and adding predators. That goal will not be reached in the present political configuration, especially because by law, state Fish & Wildlife must be “consulted” to create ranges. F&W is not any friendlier to wild animals than is FOA, so I wouldn’t hold my breath.

    Liked by 1 person

  12. What other tortures can “they” dream up to use on the wild horses and burrows of America? And, why should people of this calibre be allowed to oversee these animals??? The USA., IS NO BETTER THAN A LOT OF THE BACKWARD 3rd WORLD COUNTRIES, THAT CONTINUE MID-EVIL PRACTISES! I SAY ITS HIGH TIME TO REPLACE THE CURRENT STAFF AND REPLACE THEM WITH PEOPLE THAT HAVE COMPASSION TOWARDS OTHER LIVING BEINGS!


  13. I don’t think anyone doubts that PZP is one of the tools that can be used for reducing some wildlife populations – including wild horses and burros. But we are not talking about the need to control the populations of abandoned and scavenging and starving dogs on the streets of Tijuana and other cities.

    We are talking about wild horses and burros who have legally designated lands set aside for them under the laws of Congress. In 1971, when Congress unanimously passed the Wild Free-Roaming Horses and Burros Act, these animals were found roaming across 53,800,000 million acres. That amount of acreage could support more than about 250,000 wild horses and burros.

    If you doubt my posted BLM annual herd increase examples (and no, I am not a member of FOA and my figures come from BLM – not FOA) of 153% increase in ONE year and 187% increase in ONE year, take a look for yourself at the Herd Stats because there are even far more exaggerated statistics than these examples. BLM uses these fabricated and impossible herd increases to pull the wool over the advocates eyes as well as the government funding decision makers.

    Why doesn’t the BLM provide scientifically substantiated and credible population increases – i.e. GoPro? Because they have no evidence of any excess wild horse and burros.

    I know that different Wild Horse and Burro legal land varies but why aren’t the organizations that support PZP doing fly-overs and scientific studies on the TRUE populations? Why? Because there is no evidence of any excess wild horses and burros on their legal land.

    There is NO reason for these wild horse and burro removals and destruction procedures … because there are NO excess wild horses and burros on their legally designated land.


    • Grandmagregg , I appreciate what you say here . It would be so simple and straightforward to use the GOPRO method to visibly really see the herds . I guess anyone with the means could do this . If there really is no excess Wild Free~Roaming Horses & Burros , Then what can I say or do as a Wild Horse advocate ? If that really is the bottom line , That there is plenty of land, and no need for round~ups , and birth control , What can we say ? what can we do ? I have been so far , in support of the use of PZP but only with the greatest care, monitored closely and only in certain situations .


      • Judy, just stepping in here, but it seems to me what we MUST do is demand accountability for any population estimates in ways which include citizen scientistst and replicable, on the ground, counting results. The BLM should no longer be allowed to fabricate or continuously produce illogical and/or unverifiable numbers from which management strategies are then implemented.

        As it now stands they can fabricate numbers, AMLs, and AUMs to suit any particular agenda of the moment without any credible way for citizen scientists and citizen stakeholders to verify and hold them to account.

        This circumstance is something we can and should demand be changed ASAP.


      • Exactly.
        The BLM is in violation of Title 18. Making false statements or using any false writing or document knowing the same to contain any materially false, fictitious, or fraudulent statement or entry; is punishable by law and shall be fined under this title and imprisoned for up to 5 years. https://www.law.cornell.edu/uscode/text/18/1001


  14. This has been the agenda from the beginning.


    BLM’s Final Solution for the Wild Horses and Burros (excerpts)
    December 22, 2009

    Internal documents from the Bureau of Land Management (BLM) shed light on the agency’s motives and plans for the wild horses and burros.

    Two reports issued by the BLM for internal use only, The Herd Management Option Plans from October 2008, and the Team Conference Calls Report from July-September 2008 contain astonishing proposals to manipulate the WFRHBA and NEPA, eliminate the wild horses and burros altogether from the wild, and until they can be euthanized or sold most likely for slaughter, sterilize them and place them in feedlots paid for by rescue organizations duped into thinking the animals are in private “preserves”.

    BLM team members involved in these discussions included
    Alan Shepherd
    Jim Stratton,
    Rob Jeffers,
    Al Kane, DVM;
    Jim Johnson,
    John Neil,
    Lili Thomas,
    Gus Ward,
    Bud Cribley, and Don Glenn.

    Internal documents from the Bureau of Land Management (BLM) shed light on the agency’s motives and plans for the wild horses and burros.

    Two reports issued by the BLM for internal use only, The Herd Management Option Plans from October 2008, and the Team Conference Calls Report from July-September 2008 contain astonishing proposals to manipulate the WFRHBA and NEPA, eliminate the wild horses and burros altogether from the wild, and until they can be euthanized or sold most likely for slaughter, sterilize them and place them in feedlots paid for by rescue organizations duped into thinking the animals are in private “preserves”.

    In these 2008 reports BLM employees and consultants discussed placing the wild horses and burros in LTH facilities on public lands by converting grazing rights for cattle. To do this legally, requires changing the status of the horses and burros from wild to titled or owned livestock. The WFRHBA protects wild horses on public lands, meaning they can’t be corralled in LTH there. BLM team members discussed that to keep the animals in LTH on public lands, they would create non-reproducing herds:


  15. To answer Judy Bernard & others, careful use of PZP in selected herds with selected mares — those that have contributed to the gene pool – is one way to prevent roundups. This requires partnership with local BLM, not shooting “the Man” in the eye as FOA tries to do. Among other solutions beside predators: Insist that those in holding, starting with geldings, be repatriated to some of the 22 million acres that were taken from WHB herd areas. Promote AUM swaps to get livestock out and more land for WHBs.

    Advocates’ numbers don’t seem to have grown since the time of Wild Horse Annie, and we appear to be as divided as ever. This only benefits the cattle barons & extractive industry kings that want mustangs & burros off the land that rightfully belongs to them. We’ve been hollering about false census and absurd ALM numbers for decades with no change. I’ll keep my voice up on this, but meanwhile…The only positive change is occurring at the grassroots level, and FOA wants to end that — in favor of what? More catastrophically ruined WH “sanctuaries” like Karen Sussman’s? More roundups and slaughter threats and undercover slaughter?

    We need to swallow some differences and work together to defend public lands and WHB’s place on them. (Our CO network has members with varying views on the PZP issue, for example.) We need to forge more links with wildlife groups. We must get political: meet with our Congressional and State representatives and flood them with telephone calls when issues arise. Petitions don’t work; hand-wringing on FB only feeds egos; but calls take up Congressional staff time and they are tabulated, believe me. Finally, we need to get the positive stories and images out about WHB families & their place in the ecosystem, as well as the abusive photos of roundups and horses languishing in holding, at taxpayer expense. Those videos and photos need to get a HUGE audience. People in the US care about animals, but too few know what’s happening to our wild equine national treasures. Send the clips to The Dodo, to nature sites. Persist in this. Never give up. Share what works on the ground.


  16. I think what we must understand is that the decisions are made at the very top/ D.C. level. There are, undoubtedly, BLM people who don’t like what’s happening any more than we do, but they don’t set the policies or make the decisions. They just carry out the orders from headquarters.


  17. At first I thought PZP was a good solution but as I did more research I changed my mind.
    The roundups and removals have continued even when PZP is used
    It does work to keep advocates divided and from targeting the real problems.. bogus population claims and Wild Horse & Burro Herd Areas that have completely disappeared.
    You can’t negotiate with agencies that don’t play by the rules

    America’s Vanishing Wild Horses (excerpts)
    By Ginger Kathrens

    Over 85% of the wild horse herds are not viable. Simply put, there are not enough animals in a herd to avoid inbreeding. Unless we can reverse this irresponsible and cruel management trend, wild horses could soon be just images on a screen or pictures in a book. Just how many wild horses need to live in a herd to survive in the long term – to maintain their genetic health? Probably several hundred, preferably far more. Only about one-third of the herd members are the reproducers – the band stallion and his adult mares. The remaining two-thirds are bachelor stallions, old mares, foals, yearlings, and two-year-old fillies.

    Perhaps, just as insidious, is the experimentation with drugs on wild horse herds like Cloud’s. I hesitate to make a blanket condemnation of PZP, the infertility drug used in the Pryors and elsewhere. It is an invaluable tool in zoos. And perhaps it has some merit in viable wild horse herds – large herds with no predation and few natural threats.
    However, I do condemn its use in Cloud’s mountain home where predators killed all but one foal last year, where lightning has taken an entire family at one time, and where winter weather is a regular killer. All the foals and older horses died in a winter storm in the 1970s.
    Sadly, two young mares who received the infertility drug have just given birth this late in the year. The drug no doubt wore off last fall and the fillies were bred out of season only to foal out of season. These September newborns have little chance of surviving, for winters in Montana are harsh and it is not the time to be a nursing foal. Nor is it the time to be the mother who nurses that foal. Her life is also in jeopardy. The typical foaling period is mid-May to mid-June and this year was typical except there was a higher percentage of mares foaling. Remember I said only one foal survived last year? Well, the mares responded, giving birth in larger numbers. This is nature’s way to compensate for a declining population and is known as compensatory reproduction. Round ups have the same effect. Suddenly the population is dramatically reduced and the mares respond with higher foaling rates. I think it’s fascinating to be able to study these natural phenomena.
    But BLM is not known for watching or studying nature at work. Only about 3% of their budget to manage wild horses is allocated to monitoring the herds and inventorying the range they live on. Instead the focus is on rounding them up. As noted animal advocate Andrea Lococo has stated it, “BLM seems ‘hell-bent’ on getting rid of as many wild horses as it can, before new legislation can stop the slaughter.”


    • Horse people know this, but others may not so it bears clarifying.

      When mares “respond with higher foaling rates” it doesn’t alter the biological imperative that a single mare produces only a single foal in a single year (twins are rare and one often fails to survive). Compensatory reproduction means more mares carry to term, not that any mare produces more foals in a given year. Some of this reproductive success is linked to an increase in food resources when a given population is suddenly decreased by natural or unnatural means. Conversely, when resources are overtaxed, horses become too thin and unthrifty, and less likely to conceive and/or carry a healthy foal to term.

      Domestic mares are notoriously difficult to both get and keep in foal, with conception rates (even with the best of care) somewhere around 85%, and mares will readily abort even healthy pregnancies under various stressors.

      Even today, after 46 years of paid professional wild horse management in the United States, we have very little good information on the conception, abortion, or foal mortality rates in wild herds, so it is important to understand mares cannot produce more than one foal per year, even in compensatory reproduction mode.


  18. It’s true that we just don’t have enough data to truly understand much of anything about Wild Horses or Burros in the wild.
    They haven’t been managed as a Wildlife species
    Band behavior is probably the most central component of their ability to remain and thrive in the wild.

    Op-ed: Wild horse contraception not without unintended consequences(excerpts)
    By cassandra nunez, jim adelman and dan rubenstein

    Behavioral ecologists have long considered mare fidelity, group stability and reproductive behavior crucial to the well-being of natural feral horse populations. As referenced above, if we include these behaviors, several populations have shown important behavioral changes with PZP treatment. Suggesting that important behavioral changes must include massive reorganizations of a species’ social system, as Kirkpatrick does, sets an unrealistic standard.

    Again, we agree with Kirkpatrick that PZP is the best means currently available for managing feral horses in the U.S. His recent op-ed accurately highlighted several important benefits of PZP, including increased body condition, increased longevity and, critically, the need for fewer roundups.

    However, dismissing research that identifies PZP’s unintended consequences also dismisses opportunities to optimize wild horse management. Our response merely serves to clarify our research and reiterate our position that as with any valuable tool, PZP’s use should be carefully and continually evaluated when possible.

    Cassandra Nuñez is adjunct assistant professor of Natural Resource Ecology and Management at Iowa State University. Jim Adelman is an assistant professor in the Department of Natural Resource Ecology and Management at Iowa State University. Dan Rubenstein is a professor at Princeton University who studies the behavior and ecology of horses, zebras and wild asses



Care to make a comment?

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

WordPress.com Logo

You are commenting using your WordPress.com 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

This site uses Akismet to reduce spam. Learn how your comment data is processed.