Bioscientifica Proceedings

Summary. Limiting the abundance of free-ranging ungulate populations is a significant issue for natural resource managers in many areas of North America. Hunting and culling have traditionally been used to regulate wild animal numbers but there are a growing number of circumstances where these methods pose significant legal, ethical, and ecological challenges, and resource managers often seek alternative approaches to population control. Decreasing fertility offers a potential non-lethal method for limiting population growth; however, current technologies suffer from a variety of technical, physiological, and regulatory problems.

Two fertility control methods, which have been tested in both captive and free-ranging elk to limit individual animal fertility, and show promise as a practical tool at the population level, are gonadotropin releasing hormone agonists and vaccines. While each uses a different method of action, the end result is the same-blocking the endocrine cascade at the level of the pituitary and suppressing gametogenesis. We tested the GnRH agonist, leuprolide acetate, in a slow-release gel formulation in female elk and found it prevented pregnancy in all treated animals for one breeding season with return to fertility the following season. Using similar methods, we tested a single injection GnRH vaccine and found that while it did not have the same level of efficacy; its effects were more persistent, lasting up to three years post-vaccination in some individuals. While our studies demonstrate that it is possible to decrease fertility of individual animals, substantial effort by managers would be needed before population level effects could be realized.

© 2014 Society for Reproduction and Fertility