Wildlife managers, along with The Humane Society of the United States (HSUS), applaud official registration of the first contraceptive vaccine for horses. The HSUS had sponsored the move by the Environmental Protection Agency after more than two decades of trial and study.

“This welcome announcement marks a watershed in the humane management of wild animals,” said Wayne Pacelle, president and CEO of The HSUS. “This is a win-win-win – good for horses, good for wildlands management and good for taxpayers. Expanding the use of this proven contraceptive should lead to a significant reduction in wild horse gathering, relocation and costly pasturing in long term holding facilities.”

In many species, including horses, the vaccine, commonly known as porcine zona pellucida (PZP) but registered under the brand name ZonaStat-H, causes the production of antibodies that bind to sperm receptor site on eggs and block fertilization. The Science and Conservation Center based in Billings, Mont., produces the vaccine, which has been used to treat more than 1,600 wild, sanctuary and tribal horses annually at dozens of trial sites across the U.S., including east coast barrier islands, western wild horse ranges, Navajo and Pima/Maricopa tribal horses.

Elsewhere, PZP has been successfully demonstrated in trial programs for more than two decades. With its registration as a safe and effective product, ZonaStat-H will become more readily accessible as a management tool to control wild horse populations.

PZP was first used on wild horses in 1988 when a team led by Jay F. Kirkpatrick, Ph.D., the director of the Science and Conservation Center, began a pilot project on the famous wild ponies at Assateague Island National Seashore off the coast of Maryland. This project, which has been supported by The HSUS for more than 20 years, was so successful that the National Park Service began to utilize PZP as a population management tool in 1994.

“We have put a great deal of time, care and effort into the development of this vaccine, and official registration is a tribute to the many people and organizations that have put it to work to help wildlife over the past 24 years,” Kirkpatrick said.

“The contraceptive PZP has proven to be a perfect tool for managing the wild horse population of Assateague Island National Seashore – safe, effective, and accepted by the public as an appropriate means of controlling fertility,” said Carl Zimmerman, former resource management specialist for Assateague Island National Seashore. “We’re very fortunate to have a played a role in helping develop and test this ground-breaking technique.”

The successful use of this vaccine on Assateague Island led to the implementation of the current landmark study being conducted by The HSUS in partnership with the Bureau of Land Management and financed by a grant from the Annenberg Foundation. Increased use of PZP by the BLM could save taxpayers millions of dollars over the next decade.

“The BLM is pleased to see this next step in the development of a PZP fertility control agent,” said Joan Guilfoyle, chief of the wild horse & burro division for the BLM. “We’ve been working with partners to develop fertility control treatments since the late 1970s, and with HSUS, have supported PZP development since the 1990s. It is wonderful to finally see the first fertility control agent for wild horses become registered, and we look forward to potentially longer-lasting agents following the same process.”

The HSUS continues to be a leader in the development of contraception as a humane method of managing wild animal populations. The HSUS has forged partnerships with public agencies, communities, parks, zoos, and other entities to test the vaccine to manage wildlife populations. In South Africa, The HSUS is conducting a series of immunocontraception field tests on elephants. And, by making immunocontraception technology available to zoos, we are helping to alleviate the suffering that results from the excessive breeding of wildlife in captivity.

The Humane Society of the United States is the nation’s largest animal protection organization — backed by 11 million Americans, or one of every 28. For more than a half-century, The HSUS has been fighting for the protection of all animals through advocacy, education and hands-on programs. Celebrating animals and confronting cruelty — On the Web at humanesociety.org. Follow The HSUS on Twitter. See our work for animals on your iPhone by searching “HumaneTV” in the App Store.