Fertility Control Vaccine Approved for Wild Horses

The U.S. Environmental Protection Agency has announced the registration of the first approved contraceptive vaccine for horses. It is hoped that the use of this contraceptive will eventually lead to a significant reduction in wild horse gathers and the relocation of captured horses to long-term holding facilities.

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 sites on eggs, blocking fertilization. It is effective in horses and several other species of animals.

Registration follows years of testing in trial programs. PZP was first used in 1998 on wild ponies at Assateague Island National Seashore off the coast of Maryland. The project was so successful that the National Park Service began to utilize PZP as a population management tool in wild horse herds in 1994. The vaccine has been proven safe and effective, and is generally accepted by the public as an appropriate means of controlling fertility.

“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 Bureau of Land Management. “We’ve been working with partners to develop fertility control treatments since the late 1970s, and have supported PZP development since the 1990s. It is wonderful to finally see the first fertility control agent for wild horses become registered.”