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Deer Immunocontraception at NIST

January 2009

Contact: Michael E. Newman
(301) 975-3025

The sight of deer prancing blissfully through the woods and fields of the Gaithersburg, Md., facility of the National Institute of Standards and Technology may be beautiful, but it also represents a potential headache for the agency.

Unchecked, a deer herd can double in number every three to five years. Overpopulation is dangerous for both man and beast. Automobiles, starvation and disease threaten deer survival; humans risk severe damage to their cars and personal injury from collisions with the animals.

To better manage its deer population, NIST has partnered for the past decade with the Humane Society of the United States in the use of an innovative scientific means of birth control for wildlife. In 1996, NIST’s does started receiving two doses of porcine zona pellucida (or PZP) immunocontraceptive. The so-called “vaccine against pregnancy,” PZP is a protein taken from pig eggs that allows boar sperm to attach to a sow’s ova. Injected into females of other species, PZP elicits antibodies against that animal’s sperm-recognition protein. Sperm are blocked from entering the egg, thereby preventing conception.

In the initial inoculation attempted in the spring of 1996, 39 NIST does were injected with their first dose of the PZP vaccine. They received a second dose before the fall 1996 mating season to confer a year’s resistance to pregnancy.

Unfortunately, the first year’s trial was not as successful as hoped. The adjuvant (carrier solution) used in 19 of the inoculations interfered with the vaccine’s ability to control conception. The other 20 used a different adjuvant that did not interfere and among these deer, the vaccine was about 70 percent effective.

Fortunately, subsequent vaccinations have proven more successful. In the first four full years of the program (1997-2000), the number of births was cut approximately 72 percent from 76 to 21. The new fawns in all three years were likely the result of conceptions in NIST does who did not receive any vaccine or only got one shot, in NIST does who were off the campus during vaccinations, in stray does who moved in after vaccinations were completed, or in a small number of NIST does where the vaccine failed to work.

During the fourth vaccination round in 1999, 12 does were taken off the vaccine to see if they could become pregnant again. All 12 successfully gave birth to healthy fawns.

Since 2000, the birth rates have continued to stay low. Data have shown that the decreased birth rates are the result of the PZP vaccine.

Concurrently with the reduced birth rates, the deer population has stabilized. Nearly 300 in number back in 1997, the current NIST resident population hovers around 200. NIST expects a significant decrease in the population during the next five years as 100 percent of the does are now being vaccinated with PZP and many of the resident deer are reaching the limit of their natural life span.

Two-shot PZP vaccination programs, sponsored by the HSUS, have been more than 90 percent successful at blocking pregnancies for one year in white-tailed deer and wild horses in other areas of the country. In addition to its proven effectiveness, the PZP vaccine can be delivered easily by darts, cannot pass into the food chain, does not affect normal mating behavior, shows no side effects and allows a return to fertility when no longer administered.

The Humane Society, as co-sponsor of the NIST immunocontraception program, also uses the ongoing project to train park wildlife managers, zookeepers, and others wishing to learn the technique.