The Environmental Protection Agency (EPA) has officially registered the first contraceptive vaccine for horses after more than two decades of trial and study. The registration was sponsored by the Humane Society of the United States (HSUS).

"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 … pasturing in long term holding facilities."

In many species, including horses, the vaccine (commonly known as porcine zona pellucida and 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 United States, including east coast barrier islands, western wild horse ranges, and 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