Immunocontraception: Ounce of Prevention Proves Better Cure

In this two-part series on immunocontraception, AWI will explore the technology and discuss the politics inherent to its use. In this article, AWI provides background information about immunocontraception. In part two, to be published in the Winter 2012 AWI Quarterly, the politics of immunocontraception will be explored in greater detail.

Scientists, citizens, and many animal welfare advocates are increasingly supportive of immunocontraception as a humane method of controlling wildlife populations in lieu of traditional lethal methods (regulated hunting, trapping and poisoning) or translocation. Immunocontraception has been successfully used in more than 85 different wildlife species.

Yet, while immunocontraception offers a nonlethal solution to conflicts between people and wildlife, it remains controversial. Despite proven safety and efficacy, the use of immunocontraception to control deer fertility in urban and suburban areas is particularly contentious. State fish and game agencies are exceedingly suspicious of any wildlife contraceptive used on free-ranging wildlife, and some pro-hunting organizations are attempting to get laws passed that would prohibit states from using wildlife contraception altogether.

To date, immunocontraceptive research and management applications have largely focused on two vaccines: porcine zona pellucida (PZP) and gonadotropin-releasing hormone (GnRH). Because of its use as a non-commercial wildlife contraceptive vaccine, PZP is granted an “investigational new animal drug” exemption from US Food and Drug Administration (FDA) approval requirements. This exemption allows its use in research and field studies. The regulatory authority for use of PZP in free-ranging wildlife, however, is being transferred from the FDA to the US Environmental Protection Agency (EPA)—which is currently in the process of registering the vaccine for use beyond research.

PZP has been successfully used on wildlife populations such as elephants, horses, elk, and whitetailed deer since the late 1980s. It works by stimulating the body to produce antibodies which neutralize proteins required for egg fertilization. Once administered, it is effective for one or more years in the field. It can be administered via dart, sparing the need to capture and tag animals unless otherwise required by municipal, state or federal mandates. Research efforts are ongoing to develop a one-shot vaccine with a longer period of efficacy.

GonaConTM is a GnRH vaccine developed by the National Wildlife Research Center of the USDA’s Animal and Plant Health Inspection Service, and approved by the EPA as a “restricted-use” pesticide under the Federal Insecticide, Fungicide, and Rodenticide Act. Although GonaConTM is not a pesticide, the EPA labels it as such due to limitations in regulatory mechanisms to effectively manage immunocontraception vaccines (a limitation that must be resolved).

In order for GonaConTM to be used in any given state, it must be registered with that state and approved for use by the state fish and game agency. GonaConTM works by blocking gonadotropin-releasing hormones and thus shutting down the reproductive processes of both males and females, but can cause abortions in certain species, including bison, cattle, deer and goats. Although GonaConTM can be administered by dart, for now animals injected with the vaccine must, by policy, be trapped and tagged, which limits its practical application and increases its potential to cause stress in treated animals. Because the vaccine indirectly blocks the production of sex hormones (e.g., estrogen and testosterone), it also affects behavior.

Despite the documented success of immunocontraception use for wildlife, those who oppose this nonlethal technology have been unrelenting in their attacks. Fortunately, their arguments have largely been refuted by the science. The accusation that it does not work has been laid to rest by numerous publications describing various successful projects—including those involving wild horses at Assateague Island National Seashore, and white-tailed deer at the National Institute of Standards and Technology campus, Fire Island National Seashore, and Fripp Island. In these cases, PZP has successfully controlled fertility in both individuals and populations.

Additional concerns about threats to sport hunting, genetic integrity of wildlife segments, potential effects on social behaviors, costs, and alleged ecological effects (which are also applicable to lethal control actions but rarely evaluated), have been largely resolved for the PZP vaccine. In deer, many of these concerns are irrelevant given that immunocontraception use has only been proposed for urban and suburban populations that typically cannot be hunted anyway. In addition, the purported concern from hunting groups over compromised genetic integrity for vaccinated deer is dubious given that hunting itself targets large trophy males and, hence, poses an even greater threat to the genetic integrity of the herd. And after over 17 years of research, there is little indication that PZP substantively affects wildlife behaviors.

Although PZP can extend the breeding season of treated female deer by one to two months, the energy costs are far less than that of pregnancy, parturition, and nursing. Furthermore, the claim that untreated males will expend additional energy attempting to mate with treated females during the expanded breeding season has proven not to be an issue. Nor is there evidence of a link between PZP use and increased deer-vehicle collisions as a result of an extended breeding season. The PZP vaccine, like GonaConTM, is reversible, which ensures that each animal can be provided the opportunity to contribute his or her genes to the population.

Vaccine cost is a valid issue—although the overall costs of an immunocontraception program depend on legal and program implementation requirements as well as how the economic argument is crafted. In some places where PZP has been administered effectively, private citizens have picked up the costs of the program. In other places, tax dollars are used or there is a combination of public/private financing. Training volunteers to administer the vaccine, as is done by the Science and Conservation Center in Billings, Montana, will also reduce costs.

Fears over alleged ecological or safety issues—in the event humans or non-target species consume treated animals—are also unwarranted. Ordinary animal proteins such as PZP cannot pass through the digestive tract and remain biologically active—thus eliminating prospective adverse impacts through the food chain to predators, scavengers, or humans.

Nevertheless, immunocontraception should be used cautiously and should not be applied merely to thin inconvenient animal populations. As with lethal control, the use of immunocontraception can be abused - for example, to reduce seal numbers in order to increase fish available for human consumption. Presumably, however, immunocontraceptive use would be subject to regulatory oversight and administered via management plans.

Some animal protection groups feel that immunocontraception violates the reproductive rights of wild animals. They argue that the use of contraception on wildlife discounts the interests of free-living animals to experience life on their own terms. This is a concern that should be considered, but weighed against the reality of lethal control methods that are currently used. Indeed, management decisions for deer often come down to “darts or bullets.”

Though natural regulation is certainly preferable, as the population of certain species (e.g., white-tailed deer) increase, food becomes less abundant, range conditions degrade, mortality rates increase, and human tolerance for wildlife declines. For deer in urban and suburban areas, the default management method of wildlife agencies has been lethal control. The use of lethal control to kill deer in suburban communities is rising, in fact, as is the inherent suffering of those animals targeted for removal.

Human development has, in many ways, reduced the role of natural factors in self-regulating wildlife populations. Communities are eager for solutions to burgeoning deer populations and deer-human conflicts, including deer-vehicle collisions. Dr. Allen Rutberg of Tufts University admonishes, however, that “...focusing our frustration and enmity on 'nuisance wildlife' evades our own responsibility for creating these messes to begin with.”

Based on his own observations, Dr. Rutberg suggests that “the impulse toward wildlife contraception [as opposed to lethal control] was spawned in part by a kind of diffuse suburban guilt about the destruction we’ve wreaked on the land and on the wildlife that inhabits it.”1 Acknowledging the need for contraception is the equivalent of acknowledging that we have created a problem for the ecosystem and now need to fix it in a manner that is the least punitive to wildlife.

Controversy over immunocontraceptives is not likely to subside but, given the scientific evidence, it is time to end the petty bickering regarding the ethical, social, behavioral, cultural and scientific arguments over immunocontraception in order to implement and expand the use of this technology to benefit wildlife and communities seeking humane, nonlethal wildlife management strategies.


1. Rutberg, A. (2007). Birth control is not for everyone: a response, Human-Wildlife Conflicts 1(2), 143-144.

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