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

PM PZP Injection

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

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

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

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

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

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

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

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

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

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

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

~ Marybeth Devlin, Wild Horse Advocate

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

No excess wild horses in the Pryors

PM PZP Betrayal


PZP is a risky pesticide. Will it ruin the treasured herd?

By Marybeth Devlin

The issue underpinning the use of PZP and the continuing cycle of removals of wild horses from the Pryor Mountain Wild Horse Range is: Whether there are excess wild horses. No, there aren’t. BLM creates the illusion of an overpopulation by administratively setting the maximum herd-size below minimum-viable population. The International Union for the Conservation of Nature determined that, if a herd were managed carefully per a stud-book, it could sustain itself genetically at a minimum of 500 individuals. Compare that number to BLM’s maximum: 120.

In fact, according to the latest genetic analysis, the Pryor Mountain herd is evidencing “a general trend for a decline in variations levels of the herd.” The recommendation was to “increase population size.” Yet, BLM stubbornly insists on its own failed approach of artificially limiting herd-size, declaring that it disagrees with the scientific “interpretation.”

But can the range accommodate more horses? Yes. By way of comparison, BLM allots 38 acres per cow or calf when setting the stocking-rate for livestock grazing. Thus, the 33,187 acres that compose the Pryor Mountain habitat can support 500 to 873 horses. When the WHR is restored to its original configuration, 44,920 acres, the high-bound can be increased to 1,182.

As for PZP, numerous independent studies have disproved the old theory that PZP merely blocks sperm attachment. In fact, PZP’s mechanism of action is to alter ovarian function, causing inflammation of the ovaries and cyst formation. PZP provokes an auto-immune response, wherein the pig-ovary-derived PZP antibodies attack the mares’ ovaries, resulting in dystrophy of those reproductive organs. Despite being hyped as a non-hormonal contraceptive, PZP causes “markedly depressed oestrogen secretion” in mares treated for just three consecutive years. The latter finding was disclosed by Dr. Kirkpatrick himself 23 years ago. PZP-use is associated with stillbirths, altered ovarian structure and cyclicity, interference with normal ovarian function, permanent ovarian damage, prolonged breeding season, and unusually-late birthing dates. A particularly troubling finding suggests that PZP can be selective against a certain genotype in a population.

PZP is touted as reversible; however, a recent study warned that just three years of treatment, or administration of the first PZP injection before puberty, may trigger infertility in some mares. Thus, only two PZP injections could be viewed as relatively safe, but it appears that even one injection is risky. The researchers warned that inducing sterility may have unintended consequences on population dynamics by, ironically, increasing longevity while eliminating the mares’ ability to contribute genetically.

Most pertinent to the Pryor Mountain herd is a longitudinal study on three herds treated with PZP — Little Book Cliffs, McCullough Peaks, and … Pryor Mountain. The researchers found that the birthing season lasted nearly year-round: 341 days. Out-of-season births put the life of the foals and the mares at risk. That same longitudinal study found that, following suspension of PZP injections, there was a delay in the mares’ recovery of fertility that lasted 411.3 days (1.13 years) per each year of PZP treatment. Thus, mares injected for four consecutive years (per BLM’s “prescription”) would be expected to take 1,645.2 days (4.51 years) to regain reproductive capacity. If disaster were to befall the Pryor Mountain horses, even if PZP were stopped immediately, it would take years for the herd to recover, if ever.

PZP has neither stopped nor slowed the roundups. Only lack of holding space has done that. Even the Pryor Mountain herd, injected for decades with PZP, is facing removals again this summer (per the usual three-year cycle) in addition to an intensified PZP “prescription” to be administered per an “equal opportunity program” eerily similar to Communist-China’s one-child policy. What’s ironic is that, for all the interference, BLM has achieved basically the same — or worse — record as has been attained the International Society for the Protection of Mustangs and Burros. ISPMB complies with the “hands-off” minimum-feasible management approach stipulated by the Wild and Free-Roaming Horses and Burros Act. ISPMB’s two wild herds grew 8.73 and 5.08 percent, respectively, without PZP and without removals. Pryor Mountain’s most recent report — reflecting management with PZP and with removals — grew by 8.26 percent.

BLM needs to get out of the way of Nature. Let the Pryor Mountain herd find its own appropriate population level.

(Note: Beware of petitions pushing PZP. Be sure to read everything you sign these days especially the fine print!)

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