Deer fertility control (PZP): what the research shows

What is PZP?

Porcine zona pellucida (PZP) is an immunocontraceptive. Treated does make antibodies that block fertilization. The registered deer product, ZonaStat-D, is a restricted-use product that can be given by dart or by hand. A second product, GonaCon, must be hand-injected, which means the deer has to be captured first.

What happened on Fire Island?

On the Kismet to Lonelyville section of Fire Island National Seashore, researchers darted does with PZP from 1993 to 2004, about 958 treatments in all. Deer density, which had been rising about 11% a year, fell about 10% a year from 1998 through 2006, ending at about 42% of the 1996 to 1997 peak. Only about 18 to 21% of treated does produced fawns, compared with 83.5% before treatment. Areas with limited access and continued deer feeding saw much smaller drops.

In 2016 the National Park Service adopted a deer management plan for the Seashore that combines lethal and non-lethal tools to protect the maritime forest and the William Floyd Estate.

What did other studies find?

• NIST campus, Gaithersburg, Maryland (fenced): 1,630 treatments to 311 does from 1995 to 2006; the herd fell 27% from 1997 to 2002.
• Hastings-on-Hudson, New York: 68 does hand-injected with PZP-22 from 2014 to 2017, with one booster dart about 2.5 years later, cut fawning by more than 80% for at least five years.

The Fire Island and NIST researchers concluded that contraception alone can sharply reduce suburban herds, but only with about ten years of steady effort, and that immigration of untreated deer and deer growing wary slowed results.

What does it take in time and effort?

At NIST, capturing a deer by chemical immobilization took about 11 person-hours per deer, and each dart treatment about 1.8 hours. On Fire Island, each dart treatment took about 1.4 hours. Surgical sterilization, a different approach, has been estimated at about $1,000 per deer.

Where does fertility control work best?

• Islands, fenced campuses, peninsulas and gated communities where few new deer can move in
• Habituated deer that can be approached and darted again and again
• Communities willing to fund a multi-year program and wait for results

Where does it fall short?

• Open farm country, where deer move in from surrounding land
• Crop damage happening now, since treated does still eat
• Large herds, where the cost and effort per deer add up quickly

Is it legal in PA, NJ, DE and MD?

New Jersey requires a special Fish and Game Council permit to inhibit wildlife reproduction, and inside community deer plans limits use to approved researchers. Maryland allows it only under a non-lethal Deer Cooperator operation. We found no general authorization in Pennsylvania or Delaware rules. Talk to us before planning a program.

Last updated October 18, 2026. Reviewed by DelChester Wildlife Conservation Group.

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