Population Control of Wild Horses

to gathers and fertility control treatments. If there is no oversight by the BLM the agency believes that the herds could have a 1520 percent growth rate and based on numerous studies the population numbers are susceptible to doubling every four or five years.
The population spike is mostly due to the fact that the BLM has not been removing as many wild horses or burros or doing as much population control to help slow that growth says Lutterman. However if the BLM had not been doing any management at all this growth rate would be much quicker thus getting unmanageable.
Wild Horse Fertility Population Control Methods
Because of the nature of a wild horse the majority of any vaccination protocol is done much differently than your standard domestic horses health care. Fertility control is handled mostly in one of two different ways darting or catch and release. The BLM explains that each method is chosen based on a local level because no two herds are alike.
Whether a herd can be darted depends on different factors explains Lutterman. Some main factors being if there are enough trained volunteers or BLM staff available to do the darting or if you can actually get close enough to the horses or burros to dart them.
Lutterman says that the herds that are close to major populations such as in Reno Nev. are already used to seeing people so volunteers can get a little close to dart them. More remote herds can be harder to find attract and dart so they must plan for catch and release.
Once a herd is gathered the horses are herded into corrals much like cattle on a ranch where they are given their immunocontraceptive vaccination and marked with a freeze brand that states the year the horse was vaccinated and the type of

vaccine. This way the BLM can follow up with the correct booster at the correct time.
The BLM has mainly been using one of two different fertility control methods immunocontraceptive vaccination or implant. The choice as to which method is used on which mares follows a line of factors including what has been the current method of treatment.
Oocyte Growth Factor OGF An immunocontraceptive vaccine the BLM is seeking a onedose vaccine that can cause longterm infertility for multiple years.
Porcine Zona Pellucida PZP An immunocontraceptive vaccine that requires a booster 46 weeks after the initial inoculation and annual booster thereafter
to maintain infertility.
GonaCon Gonadotropinreleasing hormone GnRH antigen vaccine called GonaConEquine. It is injected first with a primer vaccination then followed up with a booster 30 days after the primer. This particular vaccine can cause four to six years of infertility however research is very limited on this treatment.
Intrauterine Device IUD Much like a human intrauterine device the IUD that the BLM uses is a Yshaped silicone insert but its specially designed for horses. An advantage to its use is that it provides effective contraception so long as the IUD stays in the uterus. So far it appears that it can work for several years. A disadvantage is that IUDs can interfere with an ongoing pregnancy so they can only be used in nonpregnant mares. According to the BLM more than 65 percent of wild mares are typically pregnant on any given dayand in some herds the rate is over 90 percentso the sheer number of mares that would be candidates for an IUD is a limitation.
The BLM works in partnerships with universities and the United States Geological Survey for research and development projects. The BLM has issued solicitations for research projects including fertility control treatment for the wild horses and burros in the past most recently in 2021. Project proponents may submit unsolicited research proposals to BLM at any time which are reviewed by a panel and recommended for approval based on funding and agency priorities.
Pros and Cons
The use of different immunocontraceptive vaccinations are controversial. As of press time Suzanne Roy executive director of the American Wild Horse Campaign AWHC says her group has given 5185 PZP treatments to wild horses in the past three years.