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Gerald & Buff Corse, California Academy of Science |
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Elk by lake |
Although the bulk of field research on wildlife contraception has been conducted with porcine zona pellucida (PZP) immunocontraception, other fertility control technologies are being tested. At this time, most require the animal to be captured for treatment.
Steroid Hormones
Steroid hormone implants, similar or identical to human birth control methods, are widely used for contraception in zoos, where animals can be readily accessed for treatment. Such implants are effective in many kinds of animals.
Because of the need to capture animals to insert the implants, concerns about effects of steroids on animal health and behavior, and a perceived risk that steroids will be consumed by predators or scavengers, most field research on steroid contraception in free-roaming wildllife has been abandoned.
However, some field trials continue, including tests of levonorgestrel (better known as Norplant®) in koalas and grey kangaroos.
GnRH "Agonists" and GnRH Vaccines
GnRH (gonadatropin releasing hormone), a small peptide hormone produced by the brain, is the switch that controls reproductive function in both sexes. In females, blocking GnRH stops ovulation, the estrous cycle, and the production of estrogen and progesterone from the ovaries. In males, blocking GnRH stops the production of sperm and testosterone in the testes.
Researchers are pursuing two major approaches to blocking GnRH function. One is to inject the animal with a GnRH "agonist," which creates an abnormal pattern of GnRH release and causes the target organs to become insensitive. The other is to use a GnRH immunocontraceptive vaccine, which causes the body to produce antibodies to GnRH, which in turn prevent it from stimulating the production of other reproductive hormones.
Both approaches work, at least on captive animals. Surgical implants of GnRH agonists (including leuprolide and deslorelin) in females prevent pregnancies in African lions (both captive and free-ranging), in Rocky Mountain elk and free-ranging koalas. Trials of GnRH vaccines, including the USDA/APHIS product GonaConTM and a South African commercial vaccine called Improvac®, have shown promise in captive white-tailed deer, horses, pigs and brush-tailed possums.
Both GnRH agonists and vaccines can alter natural behavior, physiology and even body form in important ways. Because of these effects, The HSUS has serious concerns about the use of GnRH-based contraceptives on wildlife. However, the same effects that we consider undesirable in wildlife contraceptives (such as suppression of estrus and aggressive behavior) may prove to be desirable when applied to companion animals.
Prostaglandins
Prostaglandins are chemicals produced in different regions of the body for a variety of purposes. One purpose of prostaglandins is to help stimulate contractions in the wall of the uterus during the birth process. Abortions have been induced in white-tailed deer by administering prostaglandins by biobullet (a bullet-shaped object that can be filled with vaccine, hormone, etc., and fired at an animal) or other means. For humane reasons, however, The HSUS does not support the use of abortion inducing agents for wildlife population control.
