BLM Program Support

FERTILITY CONTROL

Fertility controlFertility control

Developing humane, longer-lasting fertility control methods was identified as the highest priority for future research in the 2021 WHB strategic research plan. A lot is known about existing fertility control options.

At uncontrolled fertility rates, wild burro and horse herds can grow by 15-20% per year or more. Lowering on-range herd growth rates can be an important part of keeping herd sizes close to AML, over time. In most cases, ‘fertility control’ means the same as ‘population growth suppression.’ Population growth suppression includes fertility control methods (immunocontraceptive vaccines, intrauterine devices [IUDs], mare sterilization, gelding, etc.) and also includes sex ratio manipulation, which reduces the relative number of mares in a herd.

Template text for NEPA related to fertility control in wild horse and burro herd management planning is always evolving in response to science and litigation. Check with your WHB State Lead or the contact listed below for recent EAs. Fertility control is not “controversial,” from a NEPA perspective, because the effects are quite well understood. However, fertility control use in wild horses and burros can be contentious, as some members of the public may be opposed to its use. Studying the ‘social acceptability’ of those opinions is generally outside the scope of any WHB decisions, and is not addressed here.

HQ261, with help from WHB specialists, state leads, and external scientists, maintains a current literature review on the effects of different population growth suppression methods. This review is often included in NEPA documents that require analysis of alternatives with fertility control. The most current literature review contains a section on fertility control vaccines and sex ratio manipulation, a section on IUDs, and section on sterilization (female or male). Check back frequently to see if an updated version is available before you publish your NEPA documents. If you become aware of new scientific literature that should be included in this analysis, or for help with responses to public comments related to fertility control, please contact Paul Griffin.

Link here to the most recent BLM WHB fertility control literature reviews (Effects of: fertility control vaccines, sex ratio manipulation, intrauterine devices (IUDs), and sterilization)

Links to PDF files with the full set of cited publications in the most current literature review are here:

Fertility control vaccines, and Sex ratio manipulation cited materials (~120 megabytes)

Intrauterine device cited materials (~30 megabytes)

Sterilization cited materials, part 1: Authors Asa to Rutberg (~130 megabytes)

Sterilization cited materials, part 2: Authors Salter to Zhang (~45 megabytes)

Download and keep the pdf files with the cited publications available at the BLM office where NEPA will be signed, in case a member of the public wants to read these files in your public room. These files cannot all be distributed to the public because many of the papers are copyrighted material that the BLM does not have a license for sharing outside of federal agency personnel.

Standard Operating Procedures for WHB Fertility Control:

BLM SOPs for fertility control vaccine and intrauterine device (IUD) application

BLM SOPs for gelding

Fertility Control General References

Natural Resources Council of the National Academies of Sciences (NAS). 2013. Using Science to Improve the BLM Wild Horse and Burro Program: A Way Forward. See Chapter 4: “Methods and effects of fertility management.”

Kane, A.J. 2018. A review of contemporary contraceptives and sterilization techniques for feral horses. Human-Wildlife Interactions 12:111-116.

Bechert, U.S., J.W. Turner, D.L. Baker, D.C. Eckery, J.E. Bruemmer, C.C. Lyman, T.M. Prado, S.R. King, and M.A. Fraker. 2022. Fertility control options for management of free-roaming horse populations. Human-Wildlife Interactions 16.

GonaCon-Equine Vaccine

Baker D.L., J.G. Powers, J.I. Ransom, B.E. McCann, M.W. Oehler, J.E. Bruemmer, N.L. Galloway, D. C. Eckery, and T. M. Nett. 2018. Reimmunization increases contraceptive effectiveness of gonadotropin-releasing hormone vaccine (GonaCon-Equine) in free-ranging horses (Equus caballus): Limitations and side effects. PLoS ONE 13(7): e0201570.

Baker, D.L., B.E. McCann, J.G. Powers, N.L. Galloway, J.E. Bruemmer, M.A. Thompson, and T.M. Nett. 2023. Reimmunization intervals for application of GnRH immunocontraceptive vaccine (GonaCon-Equine) in free-roaming horses (Equus ferus caballus) using syringe darts. Theriogenology Wild (3): 100061.

Porcine Zona Pellucida (PZP) ZonaStat Liquid Vaccine

Kirkpatrick, J.F. and A. Turner. 2002. Reversibility of action and safety during pregnancy of immunization against porcine zona pellucida in wild mares (Equus caballus). Reproduction Supplement 60:197-202.

Porcine Zona Pellucida Pellet vaccine (PZP-22)

Rutberg, A., K. Grams, J.W. Turner, and H. Hopkins. 2017. Contraceptive efficacy of priming and boosting does of controlled-release PZP in wild horses. Wildlife Research 44:174-181.

Intrauterine Devices (IUDs)

Holyoak, G.R., C.C. Lyman, S. Wang, S.S. Germaine, C.O. Anderson, J.M. Baldrighi, N. Vemula, G.B. Rexabek, and A.J. Kane. 2021. Efficacy of a Y-design intrauterine device as a horse contraceptive. Journal of Wildlife Management 85:1169-1174.

Gradil, C., C. Joonè, T. Haire, B. Fowler, J. Zinchuk, C.J. Davies, and B. Ball. 2021. An intrauterine device with potential to control fertility in feral equids. Animal Reproductive Science. doi.org/10.1016/j.anireprosci.2021.106795

Gelding

King, S.R.B., K.A. Schoenecker, and M.J. Cole. 2022. Effect of adult male sterilization on the behavior and social associations of a feral polygynous ungulate: the horse. Applied Animal Behaviour Science 249: 105598.

Mare Sterilization

Collins, G. H., and J. W. Kasbohm. 2016. Population dynamics and fertility control of feral horses. Journal of Wildlife Management 81: 289-296.