WASHINGTON D.C.––Friends of Animals on May 20, 2015 asked the U.S. Environmental Protection Agency to “consider new scientific evidence demonstrating the need to cancel the registration of porcine zona pellucida (PZP) for population control of America’s wild horses and burros, which was issued to the Humane Society of the United States in 2012,” the FoA cover letter to EPA chief administrator Gina McCarthy said.
HSUS won registration of a PZP-based immunosterilant called ZonaStat-H, developed for use in controlling wild horse and burro populations, in January 2012, after a three-year application process.
Summarized FoA Wildlife Law Program legal director Michael Harris, “HSUS requested waivers for most of the studies ordinarily required from an applicant seeking a pesticide registration, including a toxicity study, ecological effects and environmental fate guideline study, and an efficacy study. The requested waivers were granted.
HSUS “was allowed to seek its registration based on several studies conducted in the 1990s.” Harris continued, “regarding the efficacy of the drug as a wild horse and burro contraceptive. These studies conclude overall that PZP can be highly effective at reducing fertility rates among wild horses with little to no side effect. A majority of these reviews were published by Jay Kirkpatrick, a veterinarian who manufactures PZP for use on wild horses.”
Responded Kirkpatrick by e-mail on May 29, 2015, “I am not a DVM. That might help explain how much FOA understands.”
Claims side-effects were not considered
HSUS and Kirkpatrick, Harris charged, “did not consider the biological, social and behavioral effects the drug can have on wild horses.”
Since ZonaStat-H won EPA approval, Harris said, “PZP has been in widespread use. For example, the Bureau of Land Management, which has jurisdiction over the largest number of wild horse herds on federal public lands, has administered approximately 1,944 doses of PZP to wild mares. The U.S. Forest Service has used PZP on mares in the Carson National Forest and potentially elsewhere. The use of contraception generally, and the use of PZP specifically, is advocated by the U.S. Geological Survey and the National Academy of Science.”
Argued Harris on behalf of FoA, “Research has now demonstrated changes in mare stress and reproductive physiology, in addition to changes in male behavior,” allegedly resulting from use of PZP.
“For example,” Harris said, “researchers now know that PZP poses the risk of immediate physical damage to the dosed mares, can increase the mortality rate in foals born to treated mares after the PZP loses its effectiveness, can result in social disruptions among herds with treated mares that can damage long-term herd cohesion that is critical to the health of the animals, and places the wild horses at risk of a genetic bottleneck.
“Although the information regarding PZP used to support its registration is generally accurate regarding PZP efficacy,” Harris allowed, “with regards to ecological and environmental effects it is outdated now.”
Kirkpatrick fires back
Challenged ZonaStat-H developer Kirkpatrick in a May 18, 2015 op-ed response published by the Salt Lake Tribune, “Identify wild horse populations where PZP has disrupted the social structure or social behaviors of the horses. Explain why this hasn’t even happened in the Cape Lookout, North Carolina population where this theory originated.
“Identify any wild horse population where PZP has disrupted social organization or social stability to the point of decreasing reproductive success,” Kirkpatrick continued. “Explain why this hasn’t happened at Cape Lookout.
“Identify any wild horse populations where PZP has increased the length of the foaling season and resulted in decreased foal survival. Include Cape Lookout in this answer.
“Identify any wild horse population where PZP treatment has resulted in a decrease in body condition scores, or an increase in adult or foal mortality, or a decrease in longevity. Conversely,” Kirkpatrick finished, “identify any wild horse populations where PZP treatment has increased body condition scores, decreased mortality and increased longevity.”
Assessed American Wild Horse Preservation Campaign director Suzanne Roy, “This petition to the EPA to cancel the registration for PZP is a frivolous action that lacks any scientific basis and ignores decades of research on the safety, efficacy and impacts of PZP fertility control on a variety of wildlife species, including wild horses. Even Cassandra Nunez,” author of three scientific papers cited in the FoA petition, “concluded in a 2010 paper, “When the alternative (gather and removal) is considered, PZP is currently managers’ most humane and effective option for population control.’”
“The American Wild Horse Preservation Campaign — made up of more than 60 groups, including HSUS, the Animal Welfare Institute and In Defense of Animals—has been willing to accept treating mares with the anti-fertility drug PZP as a more humane alternative to gathering and shipping mustangs to costly holding facilities,” summarized Scott Sonner of Associated Press in an April 2015 review of the conflicts leading up to the FoA filing.
By contrast, Sonner continued, FoA and Protect Mustangs, of San Francisco, “say recent studies show use of the contraceptive, which keeps the horses from reproducing for two years, is having an unnatural impact on the herds’ social structure. U.S. District Judge Larry Hicks in Reno agreed in February 2015 when he blocked a roundup based partly on BLM’s reliance on a 5-year-old study that largely ignores newer data suggesting contraception prompts some mares [who have been] unable to become pregnant to leave [their original bands] in search of stallions in other bands.”
Follow the money
HSUS, Sonner noted, “has the patent on PZP, and [FoA president Priscilla] Feral and others argue they benefit financially from its use.”
Countered Kirkpatrick in the Salt Lake Tribune, “If this is true, where is the patent number? PZP is actually produced on a non-profit basis. If there were a profit to be made, why aren’t for-profit companies making the vaccine, which is not patented?”
HSUS senior vice president Holly Hazard, who more than 25 years ago worked for Feral at FoA, before heading the Doris Day Animal League, which in 2005 merged into HSUS, “We have been working with PZP for 20 years. We believe it’s the best hope for getting the wild horse management challenges under control.”
Hazard told Sonner that the conflicting animal advocacy organizations share the same “pure vision of what we’d like to see—which would be horses remaining on the range, untouched by man. But if the only argument you can make is they should be left free on the range,” Hazard qualified, “I say that they are not now and will not ever be—at least in the reasonable future. We want a solution. We don’t want to rattle our saber toward a victory that will never come.”
Sex, drugs, & FoA
While HSUS allegedly has an apparent pecuniary interest in promoting PZP, FoA has a long history of opposing the use of animal contraceptives. FoA opposition to animal experiments done to develop Neutersol [now sold as Esterisol] in 1991 influenced HSUS to withdraw temporarily from funding some of the work. The HSUS subsidiary Humane Society International later was involved in field-testing Neutersol in several other nations.
Founded in 1957 to promote low-cost dog and cat sterilization surgery, FoA continues to raise about 40% of its annual income through the sale of vouchers for discounted dog and cat spay/neuter operations. Providing spay/neuter services also occupies about 40% of the FoA program budget.
FoA president Feral has explained at least twice, in 1991 and 2008, that while FoA has not endorsed any non-surgical sterilization methods, FoA might endorse a non-surgical sterilization method if it causes less trauma to the animals than surgery, and is otherwise safe, effective, and affordable.
Feral mentioned that her considerations in deciding whether to endorse a non-surgical sterilization method would include how the method is developed and whether animals are killed to produce it. A product using stem cells extracted from tissues removed during conventional sterilization surgery would be more acceptable to FoA, Feral said, than a product using the remains of animals slaughtered for food.
Against wild horse herd reduction
But FoA does not favor any approach to wild horse herd reduction. In June 2014 FoA and the Colorado-based Cloud Foundation asked Interior Secretary Sally Jewell to protect wild horses under the Endangered Species Act, “since the Wild Free-Roaming Horse & Burro Act, which was passed in 1971, has failed to protect our wild horses,” said an FoA media release.
“Six states have already lost their wild horse populations—Missouri, Iowa, Arkansas, Texas, Oklahoma, and Kansas,” the release added.
Said FoA Wildlife Law Program attorney Jenni Barnes, ““Now there are less than 35,000 [wild horses] on public lands, where they are supposed to be protected,” Barnes said. “Our petition states that these few remaining horses are divided into even smaller herds [by government management policies], whose populations are so low that they are susceptible to being wiped out completely by a chance event or change in the environment. Instead of protecting these horses, or just leaving them alone, a government agency, the Bureau of Land Management, plans to remove even more horses from the range with expensive and cruel tactics, such as helicopter driving. Once the government labels wild horses as ‘excess,’ the Wild Free-Roaming Horse & Burro Act does not protect them.”
Jewell has yet to respond to the FoA and the Cloud Foundation, who reportedly are preparing to file a lawsuit to force a response.
“Wild Horse Annie”
The FoA and Cloud Foundation arguments have been endorsed by the International Society for the Protection of Mustangs & Burros, the oldest wild equine advocacy organization, which points out that “Wild horse and burro populations have been nearly cut in half since 1971 when Congress declared they were ‘fast disappearing from the American scene’ and responded by adopting the Wild Free-Roaming Horse & Burro Act. ISPMB was founded by Velma “Wild Horse Annie” Johnston (1912-1977), who began advocating for wild horses in 1950 and enjoyed her first legislative success in 1952.
The development of ZonaStat-H, the PZP-based contraceptive challenged by FoA, was partially funded by the American SPCA, as well as HSUS. The active component of ZonaStat-H is based on porcine zona pellucida, extracted from the ovaries of slaughtered pigs.
The potential contraceptive use of PZP was discovered at the University of Tennessee in 1972. The Science & Conservation Center at ZooMontana, founded by Jay Kirkpatrick, DVM, has produced and tested PZP-based contraceptive vaccines since 1998.
A rival product, GonaCon, developed by USDA Wildlife Services, is a vaccine based on antibodies to the hormonal triggers that produce the sex hormones estrogen, progesterone and testosterone. Tested on wild horses in the Pryor Mountains and Theodore Roosevelt National Park, North Dakota, and on urban deer in New Jersey and Maryland, GonaCon also shows promise as a contraceptive for dogs and cats.
ANIMALS 24-7 found considerable disagreement among wild horse advocates and contraceptive researchers about the use and side effects of PZP. For political reasons, however, most were unwilling to comment on the record.
An exception was Willis Lamm, a former California firefighter who retired to focus on wild horse advocacy in 1998.
“I have observed fertility-controlled herds in the Virginia Range of Nevada for many years,” Lamm told ANIMALS 24-7. “Several of us, as volunteers, kept photographic records of bands of horses in which some members had received PZP and others received other fertility control methods. Going in, we had no knowledge as to which horses had been given which form of fertility control. The mares that we determined later were provided PZP showed no ill effects. In fact, the only observable side effects were short intervals in which they did not produce foals and developed improved body scores while they rested from gestating and nursing.
“We did not observe the entire life cycles of the Virginia Range horses,” Lamm acknowledged. “However, reports from organizations that monitored Barrier Island horses on the Atlantic Coast over multiple decades indicated that the treated mares, on average, lived several years longer than untreated mares.
“We observed some behavioral issues with horses that had received contraceptives other than PZP that may have been associated with those products,” Lamm said. “The social structures of the PZP treated horses were more influenced by human interference––tourists and meddlers––than by any side effect that we could attribute to the vaccine. The horses who kept to remote areas stayed socially integrated, while the behaviors of horses, treated or not, tended to be disrupted where humans regularly imposed themselves on the bands.
How PZP works
“I also took the time to learn how PZP works, what it does and what it cannot do,” Lamm continued. “PZP is a vaccine that, simply put, produces an antibody that affects the zona pellucida (outer lining) of a mare’s egg and prevents sperm from successfully penetrating. While individuals of any species can have varying degrees of sensitivity to any vaccine, the probable deviation associated with PZP would involve the length of efficacy. Some mares produce antibodies for shorter time periods and others produce antibodies for longer time periods. Many claimed side effects of PZP appear to be impossible for the vaccine to produce.
“It seems medically possible that excessive repeated inoculations with PZP could generate antibody responses beyond the desired period, particularly in hypersensitive individuals,” Lamm allowed. “I would accept that this is an area that warrants further objective study.
“Nonetheless,” Lamm said, “keeping horse populations in balance with range resources is a range management necessity. Most of these herds are by law restricted to ranges having defined boundaries. While there is plenty of room to argue the relative value of various range management models and grazing resource priorities, the fact remains that populations eventually exceed the carrying capacity of these defined areas. Thus two practical choices are on the table––remove excess horses, or reduce the foal crops produced in these herds.
Removal vs. reduction
“Removing horses permanently excludes members from the gene pool,” Lamm pointed out. “Reducing the numbers of foals produced from each mare can help to limit herd growth without compromising the overall genetic diversity of the herd. Simply put, a larger and more genetically diverse number of mares will each contribute fewer new members into the herd in an effort to achieve balance.
“Given that the strength of free-roaming horses relies a great deal upon genetic diversity and natural selection,” Lamm concluded, “the most rational approach to herd management involves approaches that preserve the maximum possible genetic diversity.”