The Environmental Protection Agency (EPA) announced the registration of a contraceptive vaccine for horses. The vaccine, porcine zona pellucida (PZP) has been registered under the name ZonaStat-H and is the first contraceptive vaccine approved for use in equids. The active ingredient of ZonaStat-H vaccine, PZP, is produced by the Science and Conservation Center since 1998, a non-profit research laboratory located in Billings, MT. The Center produces several thousand doses of the vaccine immunogen annually, trains field personnel to use the vaccine, and maintains a database covering 24 years of use.
The vaccine, originally discovered in 1972 at the University of Tennessee, causes a reversible infertility in horses by blocking fertilization. ZonaStat-H can be delivered by hand injection, or remotely, by a small dart. The vaccine’s use in wild horses first occurred in a herd managed by the National Park Service, on Assateague Island National Seashore, off the coast of Maryland in 1988. Locally, the vaccine is used for management of the Pryor Mountain and McCullough Peaks wild horses, and several wild horse sanctuaries in South Dakota and Montana.
Beginning in 1990, the vaccine was applied to other species including urban deer, under Food and Drug Administration (FDA) experimental use exemptions. In addition to horses and deer, the vaccine has been used successfully in more than 85 species in zoos across the world, including hoofed animals, bears, sea lions, elephants and a recent study showed it was effective in exhibit bats at the Bronx Zoo. It has also been used successfully in water buffalo on the U. S. Naval base in Guam, in wapiti (elk) at Point Reyes National Seashore, CA, in feral burros on Virgin Islands National Park, in bison, on Santa Catalina Island, and in African elephants in 14 different game parks in South Africa. Regulatory authority for the vaccine was transferred from the FDA to the EPA for use in all free-ranging wildlife, but the vaccine’s use in zoo animals remains under the regulatory authority of the FDA.
The vaccine’s efficacy ranges from 85%-100% depending upon the species, and is about 90%-95% effective in horses. IN 2011 the vaccine was used to treat more than 1,600 wild, sanctuary and tribal horses annually, at dozens of sites across the U.S., including east coast barrier islands, western wild horse ranges, Navajo and Pima/Maricopa tribal horses,.
A recent United States Geological Survey economics study indicates that the application of this vaccine could save up to $7.7 million annually in the management of western wild horses. ZonaStat-H is produced by extraction of a specific protein from the membrane surrounding pig eggs. The protein causes the production of antibodies, which bind to the sperm receptor site on the eggs of the target animals, thereby preventing fertilization. It is currently the only non-barrier contraceptive that operates entirely outside of the endocrine reproductive physiology cascade of events, has no deleterious side effects, is safe to administer to pregnant animals and will not affect social behaviors.
The current registration is specifically for horses, and the sponsorship of the registration is with the Humane Society of the United States. According to Dr. Andrew Rowan, Chief Scientific Officer for the HSUS , “Wildlife fertility management is an issue of growing importance as human activities encroach further and further into wild spaces and social attitudes to animals across the globe press for more consideration for individual animals. Killing and culling to solve human-wildlife conflict is becoming less acceptable and fertility control offers the hope of a new framework for human interaction with wildlife.”