Frequently Asked Questions on IMMUNOCONTRACEPTION
(Special thanks to Jay Kirkpatrick and Rick
Naugle for additions and corrections)
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
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
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
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 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
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
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
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
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
Isn't hunting or sharp shooting cheaper
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
PZP deer research projects are underway
in seven states:
New York http://www.fairharbor.com/fhca_deer_immunocontr.htm
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
Bureau of Land Management
US Fish and Wildlife Service
Department of Commerce
National Park Service
Rachel Carson National Estuarine Reserve
Why can't we use PZP vaccine for deer in
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
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
Journal of Zoo and Wildlife Research
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.
last modified 09/14/06