Why PZP?

Dr. Jay F. Kirkpatrick believes the key to wildlife population control isn’t in culling out the existing population but in addressing its reproduction.  “If you remove them — if that’s your major management approach — you’re not addressing the problem, you’re addressing the symptom,” he said. “If you attack reproduction, you get to the source of the problem.”

That’s the approach the Science and Conservation Center in Billings, Montana has taken in its production of porcine zona pellucida (PZP), the active ingredient in a contraceptive vaccine approved and registered on February 17, 2012 (under the name ZonaStat-H) by the Environmental Protection Agency for use in horses. Kirkpatrick is one of three people who own and operate the local, nonprofit research laboratory.The center makes a few thousand doses of the vaccine each year. Robin Lyda produces it in a pair of small labs at the center and said it takes about 25 hours over a week to make one batch, which yields 150 to 200 doses.

The vaccine causes the production of antibodies that seek out similar objects and bind to its eggs, blocking what Kirkpatrick calls “molecular keyholes,” and preventing sperm from fertilizing them.  Officials with the center like to tout that it’s the only wildlife non-barrier contraceptive that doesn’t interfere with the animals’ endocrine system and wears off after a few years without re-vaccination.

The center has been producing PZP (discovered at the University of Tennessee in 1972) since 1998 under an FDA experimental use exemption.  It 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 Humane Society of the United States for more than 20 years, was so successful that the National Park Service began to utilize PZP as a population management tool in 1994.

 

Under the FDA experimental designation, the center has also  vaccinated deer and more than 85 species in zoos worldwide, including bears, water buffalo, elephants and bats.  In one instance, they managed to reduce a localized deer population by 70 percent without having to shoot a single animal other than with the dart gun used to deliver the vaccine, he said.

Since then, PZP 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 Montana’s Pryor Mountains and the McCullough Peaks area in Wyoming. With its EPA registration as a safe and effective product, ZonaStat-H will become more readily accessible as a management tool to control wild horse populations, and according to a U.S. Geological Survey, it could save as much of $7.7 million each year in western wild horse management.

Kimberly Frank of the Science and Conservation Center helped train two board members of Friends of a Legacy, who are currently certified in the use, handling, and administrating (via a dart gun) of the PZP vaccine.