One way is what has been done for ages. Sharp shoot and cull the herd. Nothing wrong with that if the animal is used for food purposes. But there is another way: PZP.

PZP works by causing an immune reaction in does that blocks sperm fertilizing eggs. Wildlife fertility control offers a humane way to manage deer populations. Researchers have developed methods of deer “birth control”— ways to keep deer from reproducing.

The Humane Society of the United States has focused on one of them: PZP (porcine zona pellucida), an immunocontraception vaccine that can keep adult female deer from becoming pregnant and has reduced deer populations by as much as half.

Surgical sterilization or ovariectomy is another option for humanely controlling deer population growth. Although it is expensive, it need only be done one time. Removing the ovaries or a large enough percentage of an area’s does has been shown to reduce deer populations by as much as 45%.

IMMUNOCONTRACEPTION: PZP

PZP works by causing an immune reaction in does that blocks sperm fertilizing eggs. Unlike some fertility control vaccines and methods that cause undesirable behavior changes, PZP simply prevents fertilization. Most importantly, because PZP is a natural protein, like all other proteins found in animals, it is safe to use and will not harm animals. PZP can be delivered to adult female deer by hand (in food) or remotely using darts shot from a dart gun.

The dart gun method is most effective given that most hunters have good shooting skills.

Recent improvements in the PZP vaccine now prevent deer from having fawns for up to three years with just one treatment. This significantly reduces the time needed to dart animals.

Since the 1990s, the HSUS has conducted several successful PZP immunocontraception research projects on deer. Here are the four biggest:

• Fire Island National Seashore (FINS) was the HSUS’s original deer study site. be darted each year and to the effectiveness of PZP on what a growing deer population had been. The deer were easily darted and the immunocontraceptive alone was shown to reduce the deer population over time.
• The National Institute of Standards and Technology (NIST) in Gaithersburg, Md. The number of deer collisions dramatically decreased, the remaining deer became healthier, and the deer population growth rate fell.
• Fripp Island, S.C., with PZP, the deer population decreased by nearly 60 %. In addition, the remaining deer were healthier, and the number of human deer conflicts fell.
• Hastings on Hudson, N.Y., showed that PZP could reduce a deer population in an area that was not bounded by water or by a fence by as much as 50 %. The treated does stayed in their territories and kept new, untreated does from moving in. The study showed that two shots given over a period of two and half years can prevent fertilization for up to five years.

Information curtesy of the Humane Society.