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January 8, 2013

Questions and Answers about Immunocontraception

A safe way to control populations humanely

The Humane Society of the United States

  • Wild horses on the range. Robert Brownell

  • The use of immunocontraception may offer a humane, nonlethal solution to conflicts between people and deer in urban and suburban areas. Rick Naugle/The HSUS

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 might play a role in controlling dog and cat overpopulation.

What are the current objectives of the HSUS's immunocontraception program?

The HSUS is working to develop the porcine zona pellucida (PZP) immunocontraceptive vaccine into a safe, effective, and practical tool for the humane control of wildlife populations. To make this goal a reality, HSUS is working on improving field techniques, demonstrating the effectiveness of immunocontraception in the field, refining the vaccine manufacturing process, and developing training standards. 

As part of this effort, The HSUS obtained, U.S. Environmental Protection Agency registration under the name “ZonaStat-H” for use of PZP on wild horses and burros in January 2012, and will be working to extend the registration to include deer and other animals. HSUS is also 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. The PZP being tested by The HSUS is produced at the Science and Conservation Center, ZooMontana, Billings, Montana.

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, her body produces antibodies to it. These antibodies attach to her own ZP proteins, preventing sperm from attaching and blocking fertilization.

How is PZP administered?

PZP is administered by hand injection or via a dart fired from a dart rifle, CO2 pistol or blowgun. Darting is preferred whenever possible, because it avoids the need to capture and handle the animal, but darting from helicopters is often the safest and most efficient way to dart African elephants.

How long does PZP last?

In earlier research, two injections were given in the initial year, followed by annual boosters. However, one-shot PZP vaccines that last two or more years have been tested successfully on wild horses, deer and other species by The HSUS and other investigators. One technology used successfully by The HSUS and its collaborators involves packaging PZP in timed-release pellets, which stimulate annual boosters.

Spay-Vac®, a different PZP vaccine produced by Immuno Vaccine Technologies in Nova Scotia, has also demonstrated one-shot, long-term effectiveness in studies involving a variety of species, including deer. One-shot procedures are rapidly becoming standard. 

Is PZP the only immunocontraceptive being tested?

Other immunocontraceptives are being developed by other researchers. The most notable of these is GonaConTM, which was developed by the USDA/APHIS National Wildlife Research Center in Fort Collins, Colo., and registered for use as a contraceptive on white-tailed deer by EPA in September 2009. GonaConTM is a vaccine that shuts down the reproductive processes of both males and females. It has been successfully tested on captive animals of many species, including deer, elk and pigs, and field testing on deer, wild horses, and other animals is proceeding.

Is PZP experimental?

With the achievement of EPA registration for PZP, supported by a long record of success on captive animals and in the field, many uses of PZP on wild horses and burros can no longer be considered experimental. Uses on deer and other species, as well as tests of novel preparations and delivery methods for PZP are still experimental, althoughPZP was developed as a contraceptive more than three decades ago, and its effects are very well known.

Has PZP been shown to reduce wildlife populations?

More work must be done to determine where, to what extent, and how fast PZP can reduce wildlife populations. At this writing, however, PZP has significantly reduced wild horse populations at Assateague Island National Seashore, Maryland., and Rachel Carson Refuge in North Carolina, white-tailed deer populations at Fire Island National Seashore, NewYork., the National Institute of Standards and Technology, Md., and Fripp Island, South Carolina, and American bison populations on Santa Catalina Island, California. PZP vaccinations are also stabilizing populations of African elephants at 14 crowded private wildlife preserves in South Africa.

What other wildlife species are being treated with PZP?

Tests on captive animals of about 100 species in about 100 zoos and aquaria worldwide indicate that PZP works very well on a wide variety of hoofstock, including antelope, deer, wild cattle, sheep, zebra, and giraffes as well as bears and sea lions. PZP has also been given to free-roaming tule elk at Point Reyes National Seashore, Calif., and water buffalo on the island of Guam. SpayVac®, an alternative form of PZP manufactured in Canada, has shown excellent effectiveness with grey seals and fallow deer, as well as white-tailed deer.

You can learn more about wildlife contraception on these websites:

Alliance for Contraception of Cats and Dogs

AZA Wildlife Contraception Center

Bureau of Land Management Wild Horse and Burro Program

Fire Island National Seashore

National Institute of Standards and Technology

Science and Conservation Center, ZooMontana

USDA/APHIS National Wildlife Research Center

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