What is immunocontraception?

Immunocontraception is a birth control method that uses the body's immune response to prevent pregnancy.

Why is The HSUS sponsoring research in immunocontraception?

The HSUS believes that immunocontraception may offer a humane, nonlethal solution to conflicts between people and wildlife in urban and suburban areas as well as a solution to local problems of animal overabundance. Immunocontraception can also help reduce the overproduction of captive animals in zoos and other facilities. In the future, it may play a role in controlling dog and cat overpopulation.

What are the current objectives of immunocontraceptive research?

The HSUS is working to develop a porcine zona pellucida (PZP) immunocontraceptive vaccine that will meet U.S. Food and Drug Administration (FDA) standards for safety and effectiveness and serve as a practical tool for the humane control of wildlife populations. We are also developing field techniques, examining the effects of immunocontraception on wildlife population growth, and exploring the potential for the use of immunocontraceptives on companion animals.

What is PZP?

PZP (porcine zona pellucida) is a protein that occurs naturally in pig ovaries. The HSUS and others are conducting research to develop a synthetic form of PZP.

How does PZP prevent pregnancy?

Zona pellucida (ZP) proteins surround the unfertilized eggs of all mammals. Sperm must attach to ZP before an egg can be fertilized. When pig ZP (PZP) is injected into a female animal, that animal's body produces antibodies to it. These antibodies attach to the female's ZP proteins, preventing sperm from attaching and blocking fertilization.

How is PZP administered?

The HSUS and its collaborators administer PZP by hand injection or via a dart fired from a dart rifle, CO₂ pistol, or blowgun. Other researchers have administered PZP via biobullet (a bullet-shaped object that can be filled with vaccine, hormone, etc., and fired at an animal).

How long does PZP last?

In the past, two injections have been given in the initial year, followed by annual boosters. However, one-shot PZP vaccines that last at least a year have been tested successfully on horses by The HSUS and its collaborators and on other species by other investigators.

In particular, Spay-Vac®, a form of PZP produced by ImmunoVaccine Technologies in Nova Scotia, has demonstrated one-shot, long-term effectiveness in studies involving a variety of species. One-shot procedures should soon become standard. Is PZP experimental?

PZP is experimental in the sense that it is being used under an Investigational New Animal Drug exemption from the FDA and has not yet been approved by the FDA as "safe and effective" for use as a wildlife contraceptive. It is also experimental in the sense that all current uses of PZP are built around scientific studies. However, the PZP vaccine and its effects are fairly well known. PZP was developed more than a quarter century ago and has been extensively tested on many species in the lab and in the field.

Has PZP been shown to reduce deer populations?

Much more work must be done to determine where and to what extent PZP can reduce deer populations. To our knowledge, there are only two locations where immunocontraception has reduced deer populations; we are proud that these were part of studies conducted by The HSUS.

• At Fire Island National Seashore, New York, The HSUS/National Park Service research team has treated deer with PZP since 1993. Population monitoring began in 1995, and approximately 200 deer have been treated each year since 1998. Two or more consecutive years of PZP vaccinations reduced pregnancy rates in treated animals by 85–90 percent. Deer population densities in the most heavily treated area rose by 11 percent annually between 1995 and 1998, then declined by 23 percent annually from 1998 through 2000.
• At the National Institute of Standards and Technology (NIST), a 574-acre federal research campus in Gaithersburg, Maryland, The HSUS began treating deer with PZP in 1996. At NIST, the population rose from approximately 200 deer in late 1995 to a peak of approximately 300 in 1997, subsequently declining to approximately 200.

Is PZP being used to manage wild horses?

PZP was first shown to prevent pregnancies in wild horses at Assateague Island National Seashore, Maryland, in 1989. The National Park Service (NPS) has been using PZP to stabilize the wild horse population at Assateague since 1994. At Cape Lookout National Seashore, North Carolina, the NPS began using PZP to stabilize the wild horse population at Shackleford Banks in 2000.

In collaboration with The HSUS and our research team, the Bureau of Land Management has tested PZP extensively on wild horses living on public lands in the western United States. Policy guidelines and biological models have been developed for the use of PZP as a wild horse management tool on public lands, but none of these herds are formally managed with PZP at this time.

What other wildlife species are being treated with PZP?

PZP is being tested on captive animals of about 100 species in about 100 zoos and aquaria worldwide. Additionally, PZP is being given to tule elk at Point Reyes National Seashore, California, and to water buffalo on Guam (in cooperation with the U.S. Navy).

PZP has also been successfully delivered to African elephants in the field at Kruger National Park in South Africa, and additional elephant field projects are underway.