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Frequently Asked Questions on Immunocontraception for Deer

From Wildlife Fertility Control, 2006

What is an immunocontraceptive?

Immunocontraception is non-hormonal form of contraception, based on the same principles as disease prevention through vaccination. An immunocontraceptive causes the production of antibodies against some essential element of the reproductive process, thus preventing pregnancy.

Is PZP the only kind of immunocontraceptive?

There are a variety of immunocontraceptive vaccines under development including vaccines against brain reproductive hormones such as gonadotropin-releasing hormone (GnRH); pituitary hormones such as luteinizing hormone (LH) and follicle-stimulating hormones (FSH); and vaccines against steroid reproductive hormones such as estrogen and progesterone. Thus far PZP has had the widest application to wildlife.

What are the advantages of PZP?

PZP fulfills the requirements of an ideal contraceptive (J. Kirkpatrick, Ph.D.) . Such an ideal would have:

  • Contraceptive effectiveness of at least 90%
  • The ability for remote delivery with no handling of animals (thus reducing stress) Reversibility of contraceptive effects (more important for some species than others)
  • No harmful effects in pregnant animals, i.e., it would be safe for use in pregnant animals
  • Absence of either short or long-term significant health side-effects
  • No passage of the contraceptive agent through the food chain Low cost
  • In short, PZP is effective, cheap, presents no danger to humans, and is not harmful to animals.

How does PZP work?

The zona pellucida is the membrane that surrounds all mammalian eggs. When the PZP immunocontraceptive is injected, the animal produces the antibodies that produced by the animal block the sperm receptors on the egg, making fertilization and thus pregnancy impossible. Jay Kirkpatrick. Ph.D. likens it to putting superglue in a lock.

How is PZP delivered?

PZP can be delivered remotely by dart, making it unnecessary to restrain an animal and thus greatly reducing stress.

Isn't darting a deer the same thing as shooting it with an arrow?

The darts used to deliver PZP vaccine are very small, approximately 3 inches long, and have a needle like a syringe, while arrows are razor tipped to cut through flesh and sinew and cause bleeding: they wound and kill. Darts do not: they hit, inject and pop out.

How many injections are needed to contracept a deer?

A new one-shot vaccine has shown effectiveness in blocking fertilization in horses for one year and is being developed for deer. Until that one-shot form of the vaccine has been perfected in deer, two shots are necessary the first year and a single annual booster thereafter unless one takes the approach in which as many deer as possible are darted the first year without looking for any significant results for that year and then given a booster the second year. This latter approach produces effective fertility control.

Aren't PZP darts dangerous?

PZP darts are brightly colored and easily picked up. After more than a 1,400 deer dartings on Fire Island National Seashore, no darts were lost and only six were not retrieved.

Can PZP be put in food?

Research is being done to determine if PZP can be safely delivered in food. Responsible researchers believe that oral contraceptives must be species-specific (that is, it must work in only that one species for which it is intended). To date, this goal presents many scientific challenges and has not been achieved.

Doesn't PZP effect deer behavior in a negative manner?

Since they do not become pregnant, treated deer cycle for a longer period than usual. Female deer can have from 2 to 4 additional estrous cycles each year. Scientific data, however, shows that the following spring treated deer not producing fawns weight more and are thus in better condition than untreated females, perhaps due to the "biological costs" associated with 9-10 months of pregnancy and nursing. Evidence suggests that by the second or third estrous cycle dominant males yield breeding privileges to younger males so that energy expenditures are shared and no single animal becomes exhausted. Other species, such as horses, do not experience additional estrous cycles. Horses vaccinated with PZP live longer than ordinary and show extraordinary good health into old age.

How many animals must be vaccinated with PZP to reduce the number of deer?

There is no simple answer. The number of animals that must be treated depends on many factors including the goal of the project. Is the goal a 20% reduction, a 50% slowing of the growth rate, or zero population growth? To answer the question concerning number of animals to be treated, one needs site-specific data on reproduction, mortality, immigration and emigration.

How fast can one expect to see a reduction in herd size?

There is no simple answer to this question. The time required will depend on the variables such as rates of reproduction, mortality, immigration and emigration, disease, weather, quality of the habitat, etc. In 2005 deer densities in Kismet-Lonelyville ,the most heavily treated area on Fire Island, were 55 percent of whqt they had been in 1995 when surveys were first started according to Allen Rutberg, Ph.D. At the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, there has been a 20% reduction in deer after 3-4 years of PZP immunocontraception.

Does PZP have FDA approval?

The use of PZP was formerly overseen by the US Food and Drug Administration (FDA). The use of PZP for wildlife now falls under the direction of the Environmental Protection Agency (EPA). The US Food and Drug Administration (FDA) has issued an Investigational New Animal Drug Document (INAD) for PZP, which authorizes the interstate and international shipment of the vaccine for research purposes and is an agreement that the investigators may pursue their contraceptive research.

Isn't PZP still experimental and unproved?

PZP is experimental in the sense that is not marketed as a commercial vaccine. It is not experimental in the sense that it is unproved. Published documents in peer reviewed journals establish it as a sound fertility inhibitor.

How much does PZP cost per dose per deer?

The cost of PZP vaccine is between $10 and $25 per dose at present and is constantly being reduced as production becomes more efficient.

How much would an immunocontraception program cost?

There is no simple answer to this question. Labor costs are the largest expense. Costs may vary according to the role played by volunteers, how many animals are to be vaccinated, how difficult it is to find the animals (the terrain), etc. Administrative costs must also be considered. Many foundations have offered to subsidize these costs.

Isn't PZP unnatural?

PZP vaccine is as natural--or unnatural--as wearing clothes, taking aspirin, using chemical lures, high tech bows, razor tipped arrows, guns, traps and poison. PZP is a protein found in the ovaries of pigs, specifically the eggs. It is no different than the protein found in a pork chop or a piece of ham.

Isn't hunting or sharp shooting more efficient than PZP?

Hunting or culling with guns or bows, as it is practiced in Pennsylvania, is not effective due to reproductive rebound. If hunting reduced numbers, the Pennsylvania deer herd would not have constantly increased during the last century, while the number of deer killed each season has also increased.

Isn't hunting or sharp shooting cheaper than PZP?

Even excluding the cost of human death and injury, both to hunters, and others including those who hit fleeing deer running in the streets, hunting is not cheap. Hunting costs can vary greatly depending upon where it occurs. Sharpshooters charge a high fee per deer plus a fee for their services. Additionally, there are many hidden costs to both hunting and professional culling including added police protection, closing of public areas, etc. In a recent, failed attempt at using sharpshooters to kill deer in Philadelphia's Fairmount Park, not only were police and park personnel required to work around the clock for many weeks, but police helicopters were used for park surveillance.

Isn't hunting or sharp shooting just as humane as using PZP vaccine?

Hunting is extremely cruel, causing intense suffering. It has been estimated that for every animal a hunter kills and recovers, at least two wounded but unrecovered animals die slowly and painfully of blood loss, infection, or starvation. Those who don't die often suffer disabling injuries. Archery wounding rates are much higher than gun wounding rates: studies done by hunters or fish and game agencies often show rates hovering around 50% although some studies show rates as high as 90%. Even chasing deer causes intense stress as was revealed by a recent scientific study in England which measured stress hormones, etc. in the blood. Chasing deer can also use up fat reserves necessary for survival in a harsh winter.

What is reproductive rebound?

Reproductive rebound is a well documented population dynamic in deer and other mammals. Deer conceive multiple embryos but the number of fawns actually born is determined by a number of complex factors including nutrition and herd density. With competition for food reduced by a sudden drop in herd numbers, younger fawns will breed and females will give birth to twins and triplets instead of single fawns.

In its 1990 report, "An Assessment of Deer Hunting in New Jersey," New Jersey Fish and Game offered a detailed example of this process. Its report shows that even during hunting seasons in which killing female deer was the objective (antlerless seasons), the remaining females had increased birthrates that not only replaced the ones killed, but increased the overall size of the herd.

What states have used, or are using, PZP on deer?

PZP deer research projects are underway in seven states:

  • Connecticut
  • Maryland
  • New Jersey
  • New York
  • Ohio
  • Virginia
  • Washington

As a result of the research at these sites, fewer fawns are being born and already in some cases, data shows a reduction in the number of deer. It should be noted that the largest of the current deer projects are all on federal land, where opposition by state fish and game agencies has no legal force.

Does PZP work only with deer?

PZP prevents pregnancy in a large number of species, including many different kinds of deer, many zoo animals, free ranging horses, elephants, water buffalo etc. At present the PZP vaccine is being used to treat more than 112 mammalian species, with sufficient data to document success in more than 50 of these species.

If PZP is non-hormonal and works for so many different species, why aren't women pressing for research on it for their use?

There are two reasons why the native PZP won't be used by women. First, PZP is made from pig ovaries--a natural product--and it is simply impossible to make sufficient vaccine to use in humans. Thus, we must wait for someone to develop a genetically-engineered form of the vaccine. Second, the time for reversibility is so variable (one to eight years after three consecutive years of treatment) that pharmaceutical companies saw only the resulting litigation and dropped research.

Have any U.S. Governmental agencies endorsed PZP immunocontraception for animals?

PZP is being used by many U.S. governmental agencies including:

  • Bureau of Land Management
  • US Fish and Wildlife Service
  • Department of Commerce
  • National Park Service
  • US Navy
  • Rachel Carson National Estuarine Reserve

Why can't we use PZP vaccine for deer in PA?

The Pennsylvania Game Commission, which controls wildlife in the Commonwealth of Pennsylvania, refuses to allow PZP vaccine to be used.

Where can I find more information on PZP immunocontraception? Articles are published in a number of scholarly journals that can be found in public libraries. Such journals include:

Journal of Reproduction and Fertility (now just Reproduction) Journal of Wildlife Management Wildlife Society Bulletin BioScience Zoo Biology Journal of Zoo and Wildlife Research Science, etc.

The National Park Service has a monograph on this topic, and the U.S. Government Printing Office has information. Edwin Mellen Press has published the papers from the 1987 International Conference on Contraception in Philadelphia. Information is also available from HSUS; Allen Rutberg, Ph.D. at Tufts University; The Science and Conservation Center in Billings, Montana; and from I.K. Liu at University of California, Davis.


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