By C.J. Winand
Deer Contraceptives (Part I)
Contraception research originally began with pharmaceutical companies interested in birth control for women. This research led to a jump start in knowledge of immunology and molecular biology with deer contraceptive development. For the past ten years we have been hearing more and more about deer contraceptives. The anti-hunters claim deer contraception or the "pill" is the new modern age panacea that will once and for all solve our burgeoning deer problems. They boldly tout contraceptives as an immediate solution, but never report on the many unknowns. Are their claims valid? Will the use of contraceptives make hunting obsolete within the next decade or two? What's the difference between fact and fiction?
From a non-hunter point of view, it really isn't hard to imagine what the general public must think about contraception for deer. And that is, although I could never kill anything, those animal rights people may have something with contraceptives. The sad truth is many people, yet alone hunters don't have any concept about the facts concerning deer contraceptives.
The balance of the next two articles is somewhat technical, but it is essential we understand all the aspects of contraceptives. Why? Because there is no doubt the anti-hunters will try to use this information against us to outlaw all forms of hunting. Nothing has more potential impact to hunting and deer management than this important subject. It's imperative that all hunters become knowledgeable on the positive and negative aspects of this controversial issue.
If the truth be told, the biological community is somewhat divided over contraceptive research. On one hand, some believe that monies (especially hunter's dollars) should not be used in a population control method, that for all practical purposes can only be used for deer in confined areas...at least for now. Others view contraceptives as a viable alternative which should be explored where hunting is not allowed.
Methods of Conception
Currently, there are three methods biologists utilize to inhibit deer conception. The first is surgical sterilization in the field. This method, however is cost prohibited and generally not practical. The use of synthetic hormones (either digested or implanted) is a second method. These hormones cause deer to inhibit or block any stimulations from the brain for ovulation to occur. Research has shown that certain physiologically inert subcutaneous (implanted under the skin) contraceptives can last up to two years. The big disadvantage to this method is the cost and time involved in trapping/handling and implanting the deer. Additionally, the same deer will have to be trapped every year or two. If you have ever trapped deer you know this is a lot easier said than done. Furthermore, the implants must be imbedded prior to the breeding season when foods are plentiful and deer are most difficult to trap. Research has shown that deer trapped and implanted with hormones during the winter months (which happens to be the easiest time to trap deer), were ineffective in preventing pregnancy. The third method is immunocontraception which "vaccinates" a deer to stimulate its immune system to produce antibodies against certain proteins involved in fertilization. It is these key proteins that surround the sperm or egg that prevent fertilization. Immunocontraception is the most widely used method and has the best potential for use in urban environments.
The first question many people ask is, "How do these immunocontraception drugs actually work?" Current research has discovered that PZP (Porcine Zona Pellucida) has the most promise as a fertility control agent. Basically, the PZP vaccine causes chemical layers surrounding the doe's egg(s) to become impervious to sperm so fertilization can not occur. Dr. David Samuel (author of Know Hunting) explains the biological process surrounding the chemosterilant process as "something similar to the allergy shot you get for pollens or other foreign substances that enter your body. With deer, the shot triggers the doe's immune system to build up antibodies against the antigen (i.e. PZP). When sperm tries to enter into the egg, the doe now has an antibody against PZP, and the deer remains sterile."
In its current form, PZP requires two treatments the first year, followed by an annual booster thereafter. Preliminary research has determined that does will continue to cycle as many as five times with up to a 28 percent failure rate for the contraceptive. Other research using immunocontraceptives produce an anti-sperm vaccine where the does actually become immune to sperm cells.
Methods of Administering Immunocontraception Drugs
Since we understand some of the biology involved in keeping deer from conceiving, "How do we administer these drugs?" Presently, there are three methods: oral, subcutaneous (under the skin) implants and injected darts/syringes. All the techniques have both good and bad points. Oral delivery is a method where the contraceptive is contained within a bait source such as corn. Generally, this method has proved to be ineffective because the deer don't eat enough or have an aversion to the treated bait and use by non-target animals is always a problem.
Currently, a new technique of oral delivery is being developed. It involves a biologically vectored immunocontraceptive. Basically, the goal is to genetically modify a bacteria or virus that contains PZP. Although very scary, but interesting, you can imagine the number of people who would have serious concerns about controlling the spread of a virus to humans and other non-target species. Obviously, we are a long way from developing such a virus, but research may some day find an answer.
Syringes and/or darts filled with a contraception drug injected into a deer's rump, via a special gun is probably the best method of administering drugs, especially in urban areas. But they to have some problems. The main problem develops when we have missed shots which may not be recovered and have the potential to cause harm in the environment or for curious children. Recently, "biobullets" have been evaluated as a intramuscular implant. A .25 caliber biodegradable biobullet is fired from an implant gun at ranges up to 40 yards. But again, a problem develops because we must shoot the same deer year after year. If any non-target critters digest a biobullet the vaccine deactivates itself, thus this method probably offers the best alternative to future management alternatives.
Obviously, trying to see, yet alone getting a shot at the same deer from year to year is very difficult. Dr. Robert Warren from the University of Georgia reports on a compound that is already approved by the Food and Drug Administration that induces an abortion. The abortion drug is delivered with a biobullet during the winter months. When you consider that the winter months are the best time to trap deer, large numbers of pregnant deer could be treated. Current research in Connecticut found that all the does that they shot to determine the effectiveness of the drug had aborted their fetuses. Obviously, a major problem develops here when we consider the moral and ethical objections to this method of population control.
Still, some urban folks are very adamant about getting any and all deer out of their lives...permanently. Very strong immobilizing drugs that knock the deer out within seconds are currently being developed. Once the deer is down, you simply "dispatch" the animal with a .22 caliber gun or a bolt gun (like the ones butchers use). At this point, the venison is generally distributed to various needy organizations.
Since we now know some of the basic biology and methods of application using contraception, the next article will explore a stimulated model using the drugs and the many other questions that will need to be answered before this deer population control alternative is furthered advanced.
C.J. Winand is a whitetail biologist from Randallstown, MD. He is a staff writer for Bowhunter as well as Deer and Deer Hunting Magazine. This article was originally published in the October Issue of BuckMasters Magazine.