Contraception For Wild Animals? YES!

By Dr. Priscilla Cohn

If there really are too many deer, if they really are causing irreparable damage to their environment and destroying the understory in wooded areas, and if they really present a danger to people driving cars, then the most intelligent response would be to reduce the size of the deer herd humanely and without threatening the human safety. Many people think that that is precisely what hunters are attempting to do when they kill deer during hunting season. Figures show, however, that although half a million deer have been killed every year in Pennsylvania for the last five years, the total number of deer remains unchanged or has even increased. These figures show that hunting, at least as it is practiced in Pennsylvania, does not reduce deer numbers. Perhaps at least part of the reason is because the Pennsylvania Game Commission is constantly “improving habitat”: supplying deer with everything they need, such as food and shelter, for maximum reproduction.

In an attempt to introduce some reason into Pennsylvania deer activities, PNC, Inc (Pity not Cruelty) a miniscule charitable foundation, invited Jay Kirkpatrick, Ph.D. to Pennsylvania to give a series of lectures on fertility control. Kirkpatrick, a world renowned and prize winning scientist, has worked with wildlife contraceptives for over 30 years. Using this humane method, he was the first person to limit fertility in large, free-roaming wildlife without capture; the first to test the efficacy of PZP on horses, on both whitetailed and blacktailed deer, wild African elephants, feral water buffalo, elk and on more than 100 species of wildlife in zoos. Based on his research, PZP has been endorsed or used by the National Park Service, the Bureau of Land Management, the Department of the Interior, the Department of Defense and the US Fish and Wildlife Service.

Photo by Dr. Priscilla Cohn

Many people cooperated in this effort to educate the public, including, among others: Barb Riebman of NOA. Jenny Reimenschneider of Mobilization for Animals, Dan Kunkle of Wildlife Information Center, Ginger Wolfe of Lehigh Valley Animal Rights and PLAN, Sydell Gross from the Friends of Tyler Park, and George Nagle of Nagle Associates.

The subject of Kirkpatrick’s lectures was science, the science of fertility control and in particular PZP. He presented information based on data in peer reviewed scholarly journals and thus not opinions, hearsay, or unsupported claims. The main goal of his lectures could be summed up by two words, “It works!” Data reveals that PZP is effective in reducing pregnancy and in reducing total populations of deer, horses, etc. In each lecture he repeated that there is no problem with the science. If there is any problem—and there is since the Pennsylvania Game Commission has not allowed the use of PZP in Pennsylvania—it is because of social, cultural, political or economic differences, but not science.

Kirkpatrick showed that despite claims that it does not work; in fact PZP has reduced the herd on Fire Island National Seashore, NY by 60% and at NIST (National Institute of Standards and Technology, Gaithersburg, Md.) by 40% in a shorter period of time. As he has pointed out in the past, PZP has all the characteristics of a perfect contraceptive.

1) PZP has prevented pregnancy on average over 95% of the time in treated animals; 100% in elephants, etc.
2) PZP can be delivered remotely by small darts.
3) PZP contraceptive effects are reversible.
4) PZP is effective across many species.
5) PZP has no debilitating health side-effects even after long term use in deer.
6) PZP has almost no effects on social behaviors.
7) PZP cannot pass through the food chain.
8) PZP is safe to give to pregnant animals.
9) PZP can be obtained and delivered cheaply.

The data revealed that much of the criticism leveled against PZP is invalid. Contracepted horses on Assateague Island, for example, are living longer and healthier lives. Similarly, contracepted deer, despite two months of additional cycling, are in better condition than untreated ones. With additional estrus cycles, it was claimed that male deer would wear themselves out trying to impregnate contracepted females thus depleting their fat reserves and their ability to survive a harsh winter. Data showed that adult male deer stopped trying to impregnate females, probably due to a natural drop in testosterone. As a result there was no fighting between mature males and younger males and the older deer were not exhausted trying to mate with the females that did not become pregnant. Finally, the data also demonstrated that, unlike hunting, darting deer to contracept them did not cause an increase in the number of deer/car collisions.

Finally Kirkpatrick explained once again that PZP is a protein and as such, could not pass through the food chain. Protein is broken down into amino acids in the stomach so that eating a treated deer would be no different than eating beef or chicken and would have no special effect on another animal, such as an eagle or a wolf. He also explained about a “one-shot” vaccine that has been talked about so much. If  if one is willing to give one shot the first year and then a second shot the following year, 90 plus % contraception will occur in the second year. Nevertheless, a “one-shot” vaccine that will be effective the very first year looks extremely promising and is now being tested on Fripp Island.

After learning exactly how safe and effective PZP can be, the question remains, why can’t we use PZP in Pennsylvania at least where hunting presents a danger in developed areas?

Summary of Assateague Island Work with Horses
1st year: successful in limiting births. Result: no population increase.
This continued for some time
Then a precipitous drop in population
Slowness of initial reduction due to increased health and longer life of animals, thus death came at a later age. (The same well-being seen in deer that were contracepted).
COHN hypothesis: the precipitous drop will be even more precipitous each year once the older animals start to die, but a reporter could ask Kirkpatrick this question.
Long term success achieved with one shot.

Summary of Work with Deer on Fire Island and NIST
60% reduction of deer on Fire Island.
With shorter period of contraception, still a 40% reduction on NIST.
Old formulation given once for two years produces more than 93% effectiveness the second year.
Data from Fripp Island shows favorable results for long term success of new one-shot formulation.

Arguments vs. Contraception

1) Since contracepted deer cycle for 2 additional months, it was said there would be an “energetic” drain on their system (i.e., they would be less fit

Data reveals: Deer contracepted in fall were in better condition than non-contracepted deer, on average 20 kilos heavier in the spring. By the following fall, both classes of deer weighed the same.

2) a drop in testosterone), thus did not wear themselves out. Younger deer followed females for additional cycles, but did little breeding. There was no breeding frenzy or loss of condition.

3) Deer/car accidents will increase due to PZP darting

Data reveals: no increase. Fewer accidents as reduction in numbers seen.
Cohn hypothesis: there is a big difference between darting deer and shooting them with arrows or guns. The darts hit and bounce out, apparently not causing pain as all deer in the group, whether darted or not, respond in exactly the same way. They all run, but in general for a relatively short distance. There is no blood, no severe pain to freak out the animals. Arrows shot from bows are razor-tipped and designed to cut muscle and flesh, bullets wound or kill. PA Game Commission admits hunters flush deer into the streets and thus cause car accidents (see public announcement, Oct, 10,’01). Latter fact is verified by insurance companies’ records).

4) PZP cannot pass through the food chain; a contracepted deer that was eaten could not possibly feminize anyone.

True facts: PZP is an immunocontraceptive, not a hormonal contraceptive. PZP is protein and is broken down in the stomach into individual amino acids, thus eating the meat of a contracepted deer is no different than eating the meat of any cow, chicken, etc.

Dr. Priscilla Cohn has been actively involved with the development, implementation and promotion of PZP.


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Committee to Abolish Sport Hunting / C.A.S.H.
P.O. Box 562
New Paltz, NY 12561