Success Stories

Fertility control vaccines work in a wide variety of animals

The fertility control vaccine PZP has a great track record of success. It's used in more than 100 zoos worldwide and in wild horses, bison, African elephants, urban deer and other wildlife.

Unlike other wildlife management methods - such as sterilization and culling - PZP isn't permanent. Treated animals can become pregnant if they aren't re-vaccinated.

Here are some success stories:

Wild horses

Dr. Irwin Liu of the University of California, Davis, demonstrated the effectiveness of PZP in domestic horses in the 1980s.

He was later joined by longtime researchers Dr. Jay Kirkpatrick of the Science and Conservation Center in Billings, Mont., and Dr. John Turner of the University of the Toledo School of Medicine, to test the vaccine in wild horses.

Kirkpatrick and Turner vaccinated wild horses at Assateague Island National Seashore in Maryland using barbless, self-injecting darts fired from tranquilizer guns. The vaccine prevented pregnancy in more than 90 percent of the horses for approximately 12 months.

This success led the National Park service to adopt the vaccine as part of its wildlife management plan at Assatague.

The practice is now in its 25th year. Research shows no health problems due to the vaccine. In fact, the horses at Assateague are living much longer on average and are generally in better health than when the program began.

PZP is now used in more than 20 other horse management areas by the National Park Service, Bureau of Land Management and other agencies.

African elephants

Elephants in South Africa have limited living space. Most are confined to reserves and parks of various sizes. Controlling their numbers is vital to preserving herd health and habitat.

In the past 15 years, more than two dozen studies have demonstrated the effective and safe use of the vaccine. PZP is now used in 15 parks - eliminating the need to kill animals. More information.


First transported to Catalina Island for a movie in 1924, the island's bison herd has become a signature tourist attraction.

However, as the herd grew, its habitat became unsustainable. For many years, wildlife managers rounded up the animals and transported some of their numbers to the mainland to help control the herd's population. But roundups are both costly and stressful to animals.

Seeking a better solution, scientists from the Catalina Conservancy launched a study of PZP in 2009.

Before the vaccination program, more than two-thirds of the island's cows delivered calves each year. But in the first year of the program, the number dropped to 10.4 percent. And in the second year, to 3.3 percent.

A study determined vaccination is an effective, sustainable way to manage wild bison, reduce stress to animals and the ecosystem, and avoid more aggressive and costly management practices such as roundups. The success of the program has attracted international attention from the media.

Urban deer

Research performed in three test sites between 1997 and 2000 by the Tufts University Center for Animals and Public Policy showed that PZP reduced urban deer populations by nearly 60 percent.

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Information: Animal Fertility Control Vaccine
Learn more about managing wildlife with fertility vaccine