Q & A about animal fertility control vaccines

Controlling fertility is one way to manage animal populations – both in zoos and in the wild.

Fertility can be managed by surgical sterilization, drugs that regulate hormones, and vaccines that prevent fertilization.

One vaccine, PZP, has a long history of success. It's been used since 1990 in more than 100 zoos worldwide, and for more than 30 years in wild horses throughout the United States.

More recently, it's been used to effectively manage bison and elephants.

There are other contraceptive vaccines, but this Q&A relates specifically to PZP.

How does PZP work?

PZP works on the same principle as other vaccines. But, instead of stimulating antibodies to prevent disease, it creates proteins that prevent pregnancy.

The proteins block sperm from attaching to the eggs of many (but not all) species. Pregnancy can’t occur so long as sperm attachment is prevented.

Does PZP sterilize animals?

No. It merely prevents pregnancy for a period of time. Research shows the process is fully reversible. Depending on the dosage and type of animal, PZP can prevent pregnancy for several months up to two or more years.  If an animal doesn’t receive follow-up vaccinations and boosters, it can become pregnant again.

Can vaccinated animals become infertile?

No. The process is reversible up to a point. Once the vaccine wears off, animals that are not re-vaccinated can become pregnant once again. This provides flexibility in wildlife management, unlike permanent approaches such as culling and sterilization. In cases where more population growth is desirable, managers can allow some animals to become fertile again.  Continual vaccination over time can lead to sterilization, but this can be avoided.

How is PZP administered?

Depending on the habitat and animals involved, PZP is delivered by hand or via an injection dart fired from a rifle, air pistol or blowgun. Darting is generally preferred because it avoids the need for capture and corralling, which is costly and stressful to animals.

Does darting the animals hurt them?

Risk of injury is very low. The darts are very small and light and those who perform the vaccinations are trained in how to administer the darts. Over the more than 30 years PZP has been used in wild horses, no horse has ever has been injured during vaccination. Similarly, no elephants have been injured in more than 10 years of vaccine programs in South Africa.

Is PZP harmful to animals?

Numerous studies in a wide variety of animals have shown no short- or long-term physical or behavioral side effects from PZP. In fact, research shows vaccination can help animal health by improving genetic makeup of the herd and increasing animal longevity.

Can PZP harm an animal that is already pregnant?

No. Research shows PZP presents no harm to pregnant animals or their offspring. It will not harm or end an animal pregnancy.

How effective is PZP?

Studies show PZP is about 80 to 95 percent effective, depending on the species.

Can PZP contaminate water or pass from one animal to the other?

No. It is digested by the animal and doesn't pass into the water or environment, or from one animal to another.

Is the vaccine approved and regulated?

Yes. PZP was registered by the EPA in February 2012 as the first approved animal fertility control vaccine for horses. The U.S. Food and Drug Administration also authorizes its use in animals other than horses through its Investigational New Animal Drug Exemption.

Can PZP harm a species by reducing population too much?

While sterilization and culling are permanent, PZP vaccination is reversible. If animal populations are reduced too much due to poaching, disease or disaster, vaccinations can be stopped so the population can recover.

When are fertility control vaccines a good option for animal management?

Use of fertility control vaccines should be carefully weighed along with other options for managing wild animals.

The method's track record of success in a variety of animals, along with its safety and the fact that it's not permanent, make it an important option to consider.

Economics is a factor to consider, too. While it may be less expensive to kill urban deer or poison urban pigeons, vaccination may be seen by some as a better option.

And, in some cases, vaccination can save money. For example, the U.S. Department of the Interior currently spends more than $70 million each year to round up and care for wild horses in regions where fertility control vaccines are not used. In this case, according to two published studies, use of fertility control vaccines could save taxpayers millions of dollars each year.

By increasing public awareness about fertility control vaccines, we hope they will more widely be considered as an option when appropriate.

Like this page!
Information: Animal Fertility Control Vaccine
Learn more about managing wildlife with fertility vaccine